Institute of Fundamental Technological Research

In this paper, an attempt to estimate the stage of the fatigue process using the Barkhausen noise method is studied. First, microstructural and static tensile tests were carried out and, subsequently, fatigue tests up to failure were conducted. After determination of the material behaviour in the assumed static and dynamic conditions, the interrupted fatigue tests were performed. Each specimen was stressed up to a different number of cycles corresponding to 10%, 30%, 50%, 70% and 90% of fatigue lifetime for the loading conditions considered. In the next step of the experimental programme, the specimens were subjected to the Barkhausen magnetic noise measurements. Various magnetic parameters coming from the rms Barkhausen noise envelopes were determined. The linear relationship betweenthe full-width at half-maximum (FWHM) of the Barkhausen noise envelope and the number of loading cycles to fracture was found. Specimens loaded up to a certain number of cycles were also subjected to a tensile test to assess an influence of fatigue on the fracture features

fatigue, Barkhausen noise, structural steel, fracture, mechanical properties, deformation

The paper concerns the study of changes in responses of spring for drum brake systems, due to fatigue cycles conducted at operational regimes of vehicles with respect to the number of kilometers. Three types of springs from two manufacturers were examined i.e. double cylindrical, single cylindrical, and conical helical. The springs were subjected to a durability test up to 1×106 loading cycles, covering 300-500 thousand kilometers traveled. Tensile test was used for collecting differences between results for the tested object in the as-receive state and after fatigue. Values of the Pearson correlation coefficient were used to indicate differences between tested objects before and after loading cycles. They show that the obtained results expressed a very strong correlation, which means that the elastic response of the springs during operation over a distance of 300-500 thousand kilometers did not change significantly. Taking into account the recommendations of brake system manufacturers regarding the replacement of brake drums after 150,000 and 50,000 kilometers, respectively, it can be concluded that brake springs are the most durable and reliable element of such a brake system.

drums, springs, fatigue, reliability

W artykule przedstawiono wybrane aspekty programów badawczych dotyczących zmęczenia materiałów i elementów konstrukcyjnych. Zaprezentowano projekty najczęściej stosowanych próbek. Omówiono szczegóły techniczne prowadzenia badań gotowych wyrobów (z przeznaczeniem dla przemysłu motoryzacyjnego). Podkreślono także postęp w badaniach zmęczeniowych, dzięki wprowadzeniu nowoczesnych technik optycznych. Ponieważ równie istotnym elementem badań zmęczeniowych jest ocena zmian strukturalnych na poziomie mikro, tego typu testy omówiono na przykładzie analizy strukturalnej prób przeprowadzonych dla złączy spawanych ze stali wysokowytrzymałej S700MC, zaczepów kulowych oraz śrub wytrzymałościowych.

zmęczenie materiałów, techniki optyczne, próby wytrzymałościowe, fraktografia

The paper deals with experimental attempts for determination of the mechanical resistance of various components subjected to static loading by analysis of displacement values in a 3D coordinate system using a non-contact testing method. The problem is studied on the basis of results from tests of the wheelchair and SUV’s wheel, supported by means of a PONTOS 5M Digital Image Correlation (DIC) system enabling determination of the patterns deflection at discretised facet measuring zones of an element. The objects tested extend a knowledge on the components’ behaviour under static loading within their loading capacity. Data collected in the experiments are expressed by variations of the resultant vector of deflection in the 3D coordinate system and images under loading and unloading stages as well. The results enabled to indicate the weakest zone in the wheelchair and to express an influence of the foot tire on the rim edge, giving necessary knowledge on the mechanical resistance of tested components. In case of the wheelchair a rear side and axle represent the weakest regions, while for the wheel a rim edge is the most loading sensitive region on the tire guard with respect to safety of the operational process. All data captured by DIC system as a function of time can be directly used for modelling and improving a suitability of the selected components since they can be employed as the limit levels during determination of safety factor. The experimental approach applied to the SUV wheel investigation can be also used as a procedure for wheels of other type vehicles tested either in laboratories of research institutions or technical universities.

In this work, significant strength and ductility variations are reported for AlSi10Mg parts fabricated at different orientations using laser powder bed fusion (LPBF). Hardness and surface roughness of the specimens at different orientations were measured. Tensile testing together with digital image correlation technique were conducted on the specimens. XY specimens showed the highest yield stress and ultimate tensile strength while XZ specimens showed the highest ductility. Hardness measurements for different specimens were in accordance with the tensile test results, following the same order as the UTS values, XY specimens being the highest and XY-45° (out-of-plane) specimens being the lowest. Fractography of the broken surfaces of the specimens under tensile testing revealed the microstructural features and various defects in the tensile fracture. The anisotropy in mechanical properties is attributed to the microstructural anisotropy as well as presence of various types of defects induced by the AM process, which affects the deformation and failure mechanism of the parts. Linear relationships between experimental Vickers hardness versus yield stress and UTS measurements were developed. In case of material selection for different applications, these relationships can be used as a simple tool for converting hardness and yield stress (or UTS) values to each other. An equivalent strain-hardness relationship was also proposed which can be used for health monitoring of parts subject to tensile loading.

Laser powder bed fusion, Hardness, Mechanical properties, Defects, Microstructure

The impact resistance behaviour of the plate made of the AM60 magnesium alloy at the low velocity impact perforation mode is here investigated at room temperature using a numerical approach based on experimental results. Dynamic tests were performed using an impact digital tower on the 10.0 mm thick AM60 magnesium alloy plates using cylindrical impactors with conical-nose shapes of a nominal diameter of 12.0 mm, and a nominal mass of 5.77 kg. The plates were impacted with velocities ranging from 7 to 16 m/s. During the experiments, the failure of the target plates was evaluated. Finite element (FE) model was validated using experimental results. FE simulations of the conducted experiments were performed with ABAQUS software. In simulations the strain rate dependent Johnson–Cook yield criterion with a strain hardening law was accompanied with either the ductile fracture criterion or stress triaxiality-dependent JC fracture criterion to describe the target material properties. The stress and strain distributions for different impactor velocity considered were calculated using initial impact velocity data obtained from the experiments. A range of parameters, like element size, the fracture initiation strain, friction coefficient, etc. which play an important role in the simulation, were studied. The results of numerical simulation were compared with those from the experiment obtained. A good agreement between them was achieved. The failure process of AM60 target-plate revealed that in the case of the conical-nose impactor, the ductile hole enlargement occurs during the initial stage of the impact, and subsequently, a through-thickness fracture develops causing its shear plugging failure.

AM60 magnesium alloy, Room temperature impact drop-weight tower experiment, Conical-shape impactor, Numerical study of perforation process, Elastic-viscoplastic numerical analysis

The paper focuses on experimental approaches for selected mechanical coupling components to type-approval. The obtained results have enabled to present behaviour of the following tested objects: ball (with homologation certificate), transport platform, and rigid drawbars under cyclic loading. They follow details of tests to components made of typical and high strength steels as well as various kinds of aluminium alloy, such as mounting systems, parameters of loading signals, the procedure for assessing the quality of the elements after tests as well as fatigue and fracture zones, and reasons to cracks occurrence due to loading cycles performed. Moreover, they show advantages and disadvantages of the experimental approaches.

stand test, mechanical coupling device, component, fatigue, cyclic loading, crack, fracture, requirements

The paper presents the results of Charpy impact tests conducted on the S700MC steel and its weld under the range of impact energy amounts from 50 J to 300 J. The material responses in the form of accumulated energy, force, projectile velocity, and deflection versus time are determined and discussed in detail. Fracture zones were analyzed by means of the macro-photography technique giving their features such as a shape of cracks and type of damage (brittle or ductile). In case of the parent material and weld an influence of the impact energy amount on their properties was well visible. A significant change of the fracture zone features with the increase of the energy amount was observed during an examination of the steel. The weld fracture was less sensitive on the energy amount. Physical magnitudes for the steel and the weld expressed a 30% reduction of the accumulated energy in comparison of that for the joint observed. In the case of weld the values of projectile velocity exceeded those for the parent material obtained. Deflection courses of the parent material and weld tested were the same at the initial phase of the experiment, however, finally they were higher for the weld material. The data captured during this research enabled a technical quality examination of the welding joint tested.

High-strength steel,S700MC,Weld,Impact,Fracture,Degradation

Impact resistance is one of the most critical features of composite structures, and therefore, its examination for a new material has a fundamental importance. This paper is devoted to the characterization of the fully recyclable thermoplastic ELIUM acrylic resin reinforced by glass fabric woven, which belongs to a new category of materials requiring advanced testing before their application in responsible elements of engineering structures. Its high strength, low weight as well as low production cost give excellent opportunities for its wide application in the automotive industry as a replacement of the thermoset-based laminates. The study presents an experimental work concerning the effect of damage due to low and high cyclic fatigue aging of two groups of specimens, first with the woven fabric orientations of [0°/90°]4 and secondly with [45°/45°]4, on the low impact velocity properties. The impact resistance was measured in terms of load peak, absorbed energy, penetration threshold and damage analysis. The low velocity impact results indicate that the uniaxial cyclic loading (fatigue aging) of the material leads to the reduction of impact resistance, especially at the high impact energy levels. Scanning Electron Microscopy (SEM) and Computed Tomography (CT) scan observations reveal that the damage area grows with the increase of both strain amplitude and impact energy.

elium acrylic, glass fibers, composite laminates, fatigue aging, low impact velocity, damage

Rozwój uszkodzeń wskutek obciążeń eksploatacyjnych w materiałach stosowanych w energetyce lub przemyśle motoryzacyjnym badany jest przy użyciu metod niszczących i nieniszczących. Wśród technik o charakterze niszczącym można wymienić testy zmęczeniowe lub próby pełzania, a nieniszczących metody ultradźwiękowe, magnetyczne, a ostatnio coraz częściej wykorzystywane nowatorskie techniki optyczne. W artykule przedstawiono zastosowanie technik optycznych, takich jak: cyfrowa korelacja obrazu (DIC) i elektroniczna interferometria plamkowa (ESPI) do monitorowania uszkodzeń zmęczeniowych z uwagi na ich dużą przydatność w skutecznej identyfikacji miejsc inicjacji uszkodzenia i jego rozwoju.

W pracy zamieszczono szczegóły prowadzenia badań stanowiskowych wybranych podzespołów do pojazdów samochodowych. Zaprezentowano niezbędne komponenty stanowiska badawczego do prowadzenia wymienionych rodzajów testów, jak: platformę badawczą, siłownik, systemy mocowania, urządzenie DIC PONTOS 5M - przeznaczone do bezkontaktowych pomiarów parametrów kinematycznych obiektów badań. Omówiono rezultaty prób stanowiskowych, pochodzące z testów zaczepów kulowych oraz Tylnego Urządzenia Zabezpieczającego (TUZ), przedstawiając zmiany składowych ugięcia. Zamieszczono wybrane przypadki pęknięć komponentów różnego typu i wykonanych z różnych materiałów konstrukcyjnych, zawierając spoiny oraz strefy do nich przynależne.

This paper focuses on the mechanical properties analysis of the high strength S700MC steel applied in welding joints. The research comprised mechanical tests for checking what the changes of tensile characteristics, mechanical parameters, resistance to impact, and fracture toughness look like in selected regions of the welding joint. Stress-strain curves have shown significant differences in the tensile characteristic shape and the values of Young's modulus, yield stress, ultimate tensile strength, and ductility due to the welding process applied. In the case of Charpy tests, the courses of the accumulated energy, force, deflection, and project velocity are presented, indicating the maximum value of absorbed energy, the same level of force during the first contact of the projectile with the specimens, and the significant variation of the velocity for the impact energy ranging from 50 J up to 300 J. On the basis of the fracture toughness tests, the distributions of the CTOD (Crack Tip Opening Displacement) values are presented for the parent material, HAZ (Heat Affected Zone) and weld. Moreover, the characteristic features of the fatigue pre-crack, transient and crack propagation zones are identified and discussed.

high strength steel, weld, HAZ, tensile curve, impact, fracture toughness, CTOD, fractography, S700MC

The paper concerns the study of polymer-glass composite under tensile loading in order to determine changes in the tensile characteristics. Mechanical properties and features of damage zones important for operation and assessment of the technical conditions of the components made of this material are considered. Selected details of the experimental technique used are presented. The tensile characteristics of the polymer-glass composite are given. They were determined using specimens taken from various directions, with the main focus on the Young's modulus, elastic limit, yield point and ultimate tensile strength. An influence of the number of reinforcement layers, percentage content of the glass fibres as well as the resin quantity, on the mechanical parameters, are discussed.

composite, reinforcement, anisotropy, tensile curve, mechanical properties, structure, degradation, cracking, delamination

The paper reports experimental results describing behaviour of the AM60 magnesium alloy under impact test. The material was examined at energy in the range from 170 to 690 J, using impact tower with the projectile of conical shape. Results are presented in a form of variations of accumulated energy, force, projectile velocity and its displacement versus time. The characteristic features appearing in courses of force and accumulated energy are illustrated. Fractography and microstructure of damage zones for distinguishing the alloy degradation are shown. The fracture regions of the material examined are represented by cracks and plug-shaped deformation.

magnesium alloy, impact, projectile, perforation, fractography, microstructure

W pracy omówiono przyczyny występowania uszkodzeń i ich rodzaje. Zawarto cechy charakterystyczne przełomów zmęczeniowych w odniesieniu do wskazania przyczyn ich występowania. Zaprezentowano wybrane stanowiska badawcze do testowania podzespołów motoryzacyjnych i ich wersje modułowe – wyposażane w specjalistyczne komory oraz rekonfigurowalne – zawierające gabarytową płytę montażową. Przedstawiono szczegóły testów stanowiskowych komponentów pojazdów specjalnych, jak ramy wychylne oraz stałe, w tym wykonane ze stali wysokowytrzymałej S700MC. Zaprezentowano charakterystyki naprężenie-odkształcenie, parametry mechaniczne oraz krzywe Wöhlera wymienionego rodzaju materiału w stanie dostawy i po spawaniu.

The paper presents experimental results from test on tow truck frame made of the high strength steel S700MC subjected to fatigue loading. The mounting manner of the frame with anti-vibration platform and connection with a coupling ball to apply the loading are presented. Cracks features captured by means of macrophotography and microscopic observations are illustrated. Reasons for the crack occurrence are discussed by the use of fractography, hardness tests, microstructural analysis of the parent material, Heat Affected Zone and weld.

cyclic loading, fatigue, fracture, crack, higth strength steel, hardness, microstructure, welding, HAZ

The paper reports the results of tests carried out for kinematic properties determination of components under cyclic loading. DIC system called 5M PONTOS was employed to follow variations of displacement versus time. It was conducted by the use of markers stuck on selected sections of components tested. The results are presented in 2D and 3D coordinate systems expressing behaviour of such elements as: mechanical coupling device, boat frame and car engine. These data enabled to capture weak and strong sections of the component examined at various loading conditions.

Digital Image Correlation System, Cyclic Loading, PONTOS, Motion, Displacement, 3D Coordinate System

W pracy zaprezentowano wyniki badań trwałościowych końcówki drążka kierowniczego pojazdu o dmc powyżej 3.5 tony. W badaniach wykorzystywano wielkogabarytową platformę wibroizolowaną, serwohydrauliczny siłownik mobilny oraz cyfrowy kontroler sygnałów IST Instron. Próby prowadzono w warunkach działania obciążenia zmiennego cyklicznie do uzyskania 2×106 cykli. Ze względu na kompleksową ocenę zachowania końcówki drążka kierowniczego testy przerywano, by wykonywać oględziny obiektu badań. Wyznaczono zmiany kąta wychylenia oraz momentu siły w funkcji liczby cykli oraz przedstawiono ich prognozę. Omówiono procedurę badawczą służącą ocenie trwałości przegubu kulistego.

przegub, zmęczenie, obciążenie zmienne cyklicznie, liczba cykli, trwałość, pęknięcie

W pracy omówiono wybrane materiały stosowane w układach hamulcowych, jak: żeliwo szare, kompozyty ceramiczne oraz metalowe o osnowie ze stopu aluminium. Zaprezentowano ich zasadnicze właściwości mechaniczne oraz parametry fizyczne. Ponadto, omówiono zmiany granicy plastyczności i wytrzymałości doraźnej żeliwa szarego w warunkach rozciągania prowadzonego przy dziewięciu poziomach temperatury w zakresie od 20 °C do 700 °C

W pracy omówiono technike cyfrowej korelacji obrazu (DIC) przeznaczona do bezkontaktowego okreslania rozkładów składowych przemieszczenia i na ich podstawie obliczania składowych odkształcenia oraz naprezenia. Umozliwia ona równiez wyznaczanie parametrów kinematycznych obiektów inzynierskich w postaci predkosci i przyspieszenia, które okreslane sa metoda rózniczkowania po czasie zarejestrowanych wartosci składowych przemieszczenia. Zaprezentowano polowe zmiany rozkładów odkształcenia wzdłuznego oraz rozkładów składowych głównych odkształcenia podczas rozciagania stali konstrukcyjnej, które monitorowano az do chwili zniszczenia materiału. Przedstawiono wyniki próby porównawczej, w której jednoczesnie stosowano ekstensometr oraz system DIC. Dodatkowo zaprezentowano rezultaty prób stanowiskowych mechanicznego elementu sprzegajacego przeprowadzonych przy uzyciu systemu pomiarów cyfrowych w warunkach oddziaływania cyklicznie zmiennego obciazenia.

W pracy omówiono wybrane zagadnienia z zakresu mechaniki pękania dotyczące wyznaczania współczynnika intensywności naprężenia i jego krytycznej wartości (K IC ). Zaprezentowano projekt zminiaturyzowanej próbki kompaktowej (CT) o wymiarach czterokrotnie mniejszych niż jej wersja standardowa. Zamieszczono wyniki z badań odporności na kruche pękanie materiałów kompozytowych wytworzonych na bazie odlewniczego stopu aluminium 44200 z różną zawartością Al 2 O 3. Analiza rezultatów przeprowadzonych testów wykazała brak wpływu udziału Al 2 O 3 i jego postaci, tj. włókien bądź cząstek, na zmianę krytycznej wartości współczynnika intensywności naprężenia

The paper reports experimental results from tests carried out at room temperature on servo-hydraulic system dedicated for examination of the exploitation properties of rocker arms. The ball joint of this element was modified by an application of composite coating such as the tungsten carbide (WC). To apply cyclic loading to rocker arms the griping system was designed and elaborated. Results from tests performed on the composite coated ball joints were compared with data obtained for typical elements. Variations of the following parameters versus time i.e. force, temperature and surface topography of balls were analysed with respect to exploitation properties of the modified ball joints. An increase of the wear coefficient was achieved for sliding joints of the steel ball-steel cups coated by the WC.

Ball Joint, Composite, Cyclic Loading, Surface Topography, Tungsten Carbide, Wear

The effects commonly related with deformation caused by proportional and non-proportional loading types were identified experimentally. In the case of non-proportional cyclic loading along circular strain path the second order effects such as: phase shift between stress and strain signals was observed. An analysis of experimental data from tests under non-proportional cyclic loading along square strain path exhibited a significant reduction of stress independently on direction of deformation.

The paper also presents experimental results concerning evaluation of an influence of cyclic loading on stress variations during monotonic deformation carried out on the pure copper and X10CrMoVNb9-1 steel. All strain controlled tests were performed at room temperature using thin-walled tubular specimens. The experimental programme contained selected combinations of monotonic and cyclic loadings, i.e. the torsion-reverse-torsion cycles were superimposed on the monotonic tension. It is shown that such cycles associated with monotonic tension caused essential variations of tensile stress. For both materials, a significant decrease of the axial stress was visible. The effects observed during monotonic and cyclic loading combinations were theoretically described using the Mróz and Maciejewski model.

Proportional and non-proportional loadings, Hardening, Softening, Tensile stress, Strain energy, Yield surface, Modelling

W artykule przedstawiono na podstawie dostępnych prac właściwości mechaniczne żywic i włókien powszechnie stosowanych jako składniki materiałów kompozytowych. Omówiono typy zniszczenia tego rodzaju materiałów wynikające z różnej kruchości zbrojenia. Zaprezentowano rodzaje przełomów występujące podczas rozciągania i ściskania kompozytu w zależności od kierunku pobierania próbek. Omówiono kryteria zniszczenia stosowane do oceny odporności materiałów kompozytowych dla różnych wariantów obciążenia.

The paper presents experimental results of tests carried out at room temperature on power engineering steel: 10H2M (11CrMo9-10) using thin-walled tubular specimens under biaxial stress state. The loading programme comprised different types of deformation, i.e. monotonic tension and cyclic torsion in the form of symmetric or asymmetric step-increasing strain amplitude. The main task of the paper was focused on investigation of an influence of the cyclic loading parameters on tensile curve variations. The magnitudes of axial strain and cyclic shear strain amplitude were small and did not exceed 1%. An analysis of the results showed a significant reduction of the axial stress (even equal 90% for the torsional amplitude ±0.8%, in both cases of cyclic loading). An influence of torsion frequency on the tensile stress curve was discovered within the range from 0.005Hz to 0.5Hz.

Cyclic Loading, Hysteresis Loop, Stress Variation, Tensile Characteristic

This paper presents experimental results of the fracture toughness tests carried out on metal matrix composites. The material was produced using the 44200 aluminium alloy reinforced by Al2O3 in the form of Saffil fibres. Three different contents of Al2O3 were taken into account, i.e. 10%, 15%, 20%. The main aim of the research was to examine an influence of the aluminium oxide content on a critical value of the stress intensity factor, KIC. All tests were performed using a miniature compact specimen, which was four times smaller than the typical one. The results of FEA analysis confirmed a typical distribution of the effective stress at the tip of the notch. In each test the composite specimen was mounted in the loading system of the testing machine by applying special grips. Crack tip opening displacement of the specimen notch was measured by means of the clip on knife edge extensometer having 10 mm gauge length. The results in form of tensile force versus crack tip opening displacement show the first mode of fracture. An inspection of the pre-cracked zone of the composite did not exhibit the typical features usually observed on specimen surface after fatigue. An influence of the Al2O3 Saffil fibres content within the range from 10% to 20% on a critical value of the stress intensity factor was negligible small. The KIC of the composites tested in this research achieved the level of 12 MPa m 1/2.

metal matrix composite, fracture toughness test, compact specimen, fatigue zone, stress intensity factor

This article presents the results of an analysis of the mechanical properties of the AW8S-V polyester composite reinforced by a roving fabric under tensile loading. The stress-strain curves show an increase of the maximum stress and elastic modulus with increasing strain rate. By contrast, an increase of the temperature led to decrease of the maximum stress and elastic modulus. It is also shown that, failure mechanisms are dependent on the loading type. Shear cracks occurred in the specimens under quasi-static loading whereas composite layers damage was observed under dynamic loading. Temperature increase resulted to stronger fragmentation of the specimens.

polyester composite, Hopkinson bar, high strain rate, damage

W artykule zaprezentowano współczesne maszyny wytrzymałościowe i przyrządy pomiarowe do badania właściwości mechanicznych materiałów. Zamieszczono oraz omówiono ich schematy ideowe, zalety, wady, ograniczenia i zastosowanie. W przypadku niektórych z nich przedstawiono literaturowe i własne wyniki z badań doświadczalnych.

The paper presents behaviour of materials under complex loading being combinations of torsion-reverse-torsion cycles superimposed on monotonic tensile deformation. The 2024 aluminium alloy, P91 steel and M1E copper were investigated under plane stress state using thin-walled tubular specimens. All tests were strain controlled and a total strain was less than 1%. An influence of torsion cycles on tensile characteristic was manifested by lowering of the proportional limit and yield point. This effect was increased with magnification of cyclic strain amplitude and in the case of copper a reduction of yield point was equal around 90%. A character of this effect was checked using the yield surface concept after each test. The papers also presents variations of tangential hardening modulus and plastic strain energy dissipation.

complex loading, biaxial stress state, cyclic loading, mechanical parameters

W pracy zamieszczono wyniki z badań doświadczalnych dotyczących określania wpływu obciążenia skręcającego o charakterze cyklicznym na przebieg wyznaczanej jednocześnie charakterystyki rozciągania następujących materiałów: stali P91, stopu aluminium P a7 oraz miedzi M1E. Testy przeprowadzono na cienkościennych, osiowosymetrycznych próbkach rurkowych w warunkach płaskiego stanu naprężenia przy sterowaniu sygnałami odkształcenia. Wyznaczono zmiany granicy proporcjonalności, plastyczności i stycznego modułu wzmocnienia w zależności od amplitudy odkształcenia postaciowego oraz opracowano przebiegi zmian naprężeń głównych i kąta obrotu ich kierunków.

mechanika eksperymentalna, obciążenie złożone, obciążenie cykliczne, właściwości mechaniczne, rozciąganie, skręcanie

The paper presents experimental investigations of two light aluminium alloys (AlSi8Cu3 and AlSi7MgCu0 5) under loading conditions leading to the creep or fatigue processes. During the creep process, the strains were measured under selected tensile stresses and temperatures. An influence of a step loading during creep, at elevated temperature, on steady creep rate and a course of creep curve, was investigated. Moreover, an effect of porosity degree on creep of both aluminium alloys was also analysed. An influence of aging process at the elevated temperature was experimentally evaluated. Fatigue behaviour of materials was checked under strain control using cylindrical samples. The results of LCF tests were analysed for the materials subjected to three-stage sequence of loading at elevated temperature. A resistance to creep and fatigue processes of the AlSi8Cu3 was weaker than that obtained in the case of the AlSi7MgCu0 5.

Creep, Fatigue, Sequence loading, Aluminium alloys

The paper presents experimental results concerning evaluation of an influence of cyclic loading on material behaviour under monotonic deformation. Tests were carried out on pure copper and P91 steel. The experimental programme contained the torsion–reverse–torsion cycles superimposed on the monotonic tension. It is shown that the torsion–reverse–torsion cycles associated with monotonic tension caused essential variations of the tensile characteristic. For both materials, a significant decrease in the tensile stress can be observed. The effects observed during monotonic and cyclic loading combinations were theoretically described for the 2024 aluminium alloy using the Mróz and Maciejewski model.

Complex loading, Yield point, Yield surface, Mechanical parameters

The paper presents relationships between strain level generated by creep process and two parameters determined form non-destructive tests, i.e. acoustic birefringence and amplitude of magnetoacoustic emission for three kinds of steel: 40HNMA, P91 and 13HMF. Moreover, the relationships between prior deformation level and selected mechanical parameters resulting from the standard tensile tests subsequently carried out at room temperature were established. As a consequence, this enabled to formulate mutual relationships between these mechanical parameters and parameters obtained from the ultrasonic/magnetic investigations.

creep, damage, yield point, ultimate tensile stress, Young’s modulus, acoustic birefringence, magnetoacoustic emission

The paper presents experimental results of investigations carried out on the P91 steel and 2024 aluminium alloy under complex stress states due to various combinations of an axial force and twisting moment. An influence of out-of-phase sinusoidal and trapezoidal strain signals on the mechanical behaviour of tested materials was considered. The experiments enabled identification of the second order effects connected with the non-proportional cyclic loadings such as the phase shift between stress and strain signals during the deformation along the circular strain path, and a significant stress drop of the one of loading components applied in the case of deformation enforced by the trapezoidal signals. The experimental programme also contained the tests of monotonic tensile deformation realized simultaneously with delayed torsional cycles. They enabled to observe a drastic variations of the proportional limit and yield point of the materials in the tensile direction. This fact manifests an important material feature which can be applied to the optimal designing of some metal forming processes like an extrusion or forging for example

cyclic loading, biaxial stress state, circle loading path, square loading path, mechanical parameters, yield surface

The paper presents experimental results of investigations carried out on the 2024 aluminium alloy and P91 steel under biaxial stress state. The loading programme comprised a monotonic tension assisted by torsion-reverse-torsion cycles. An influence of the cyclic loading and its delay with respect to uniaxial tension on the selected mechanical parameters taken on the basis of tensile characteristics was investigated. Additionally, a relative variation of the proportional limit and yield point due to the loading history applied was analyzed. A permanency of effects observed during combination of tension and cyclic torsion was experimentally assessed on the basis of an initial yield surface evolution

The paper presents experimental results of investigations carried out under complex stress state on the 2024 aluminium alloy (used by aircraft industry) and P91 steel (used at power plants). Second-order effects associated with cyclic loadings enforced by the trapezoidal signals in the two mutually perpendicular directions are identified. It is shown, how the cyclic loading and its parameters (strain amplitude and frequency) influence the simultaneous monotonic loading in the direction perpendicular with respect to the cyclic one. Moreover, the paper presents an analysis of the selected mechanical properties variations on the basis of an initial yield locus evolution.

kompozyty, żywice termoplastyczne, badania zmęczeniowe, udarność

In most cases, fatigue damage has a local character and it is based on damage development leading to generation of cracks appearing around structural defects or geometrical notches. An identification of these areas and their subsequent monitoring requires a full-field displacement measurements performed on the objects surfaces. This paper presents an attempt to use the Electronic Speckle Pattern Interferometry (ESPI) method for fatigue damage evaluation and its monitoring on specimens made of the P91 steel and aluminide coated nickel super-alloys. In this work, also a development of fatigue damage was investigated using destructive and non-destructive methods in materials commonly applied in power engineering or automotive industry. The fatigue tests for a range of different materials were interrupted for selected number of cycles in order to assess a damage degree. As destructive methods the standard tensile tests were carried out after prestraining due to fatigue. Subsequently, an evolution of the selected tensile parameters was taken into account for damage identification. The ultrasonic or magnetic techniques were used as the non-destructive methods for damage evaluation. In the final step of the experimental programme microscopic observations were performed. The results show that ultrasonic and magnetic parameters can be correlated with those coming from destructive tests. It is shown that good correlation of mechanical and selected non-destructive parameters identifying damage can be achieved for the materials tested

Fatigue, damage, optical methods, non-destructive techniques

The paper concerns numerical and experimental investigations carried out for determination of an influence of holes on material behaviour under monotonic tension. The 40Cr steel commonly applied in automotive and power plant branches of industry was tested. The analysis was performed by the use of analytical and Finite Element Method calculations. It enabled identification of stress concentration/maximum stress versus hole diameter relationships, and the HMH stress distribution. Full-field contactless Digital Image Correlation (DIC) system was used for capturing the effective strain variations from the beginning of test up to specimen fracture. It enabled us to indicate the most important stress concentrator, and moreover, distribution of the HMH effective strain in 2D coordinate system. A comparison of tensile characteristic obtained by means of smooth and perforated specimens showed 70% reduction of yield point and 50% lowering of elongation as an effect of the artificial defects introduced.

Monotonic tension, holes, steel, stress concentration factor, maximum stress, yield point, ductility, FEM, DIC

The effects often taking place during proportional and non-proportional types of loading were identified experimentally and modelled numerically. In the case of non-proportional cyclic loading along circular strain path the second order effects such as: phase shift between stress and strain signals were discovered. An analysis of experimental data from tests under non-proportional cyclic loading along square strain path exhibited a significant reduction of stress independently on direction of deformation. The paper also presents experimental results concerning evaluation of an influence of cyclic loading on mechanical parameters during monotonic deformation carried out on the 2024 aluminium alloy and X10CrMoVNb9-1 steel. All strain-controlled tests were conducted at room temperature using thin-walled tubular specimens. The experimental programme contained selected combinations of monotonic and cyclic loadings, i.e. the torsion-reverse-torsion cycles were superimposed on the monotonic tension. It is shown that such cycles caused essential variations of the tension characteristics. A significant decrease of the tension stress was observed. The effects occured during monotonic and cyclic loading combinations were described using Mróz and Maciejewski model. Reasonable good predictions of: hysteresis loops and stress responses for the square and circular loading paths and tensile curves assisted by torsion cycles were obtained

cyclic loading, hardening, softening, complex stress state

Selected damage measures applied for degradation description of engineering materials subjected to fatigue loading conditions are presented. In addition to well - known measures the new concepts of fatigue damage development are discussed using known mechanisms of cyclic plasticity and ratcheting. Their usefulness was studied on the basis of experimental results for modern metal matrix composites commonly applied in many branches of the industry.

Damage, fatigue, composites

This paper presents experimental results of tests carried out at room temperature on power engineering steels: P91 (X10CrMoVNb9-1), 10H2M (11CrMo9-10) using thin-walled tubular specimens under biaxial stress state. The loading programme comprised two different types of deformation obtained by monotonic tension and torsional cycles. The values of axial strain and cyclic shear strain amplitude were small and did not exceed 1%. In the case of both materials tested, a significant reduction of the axial stress was achieved. It was even equal to 90% for the 10H2M steel.

The paper is devoted to an analysis of creep damage at elevated temperatures and structural degradation due to plastic deformation at room temperature of selected steels commonly applied in power plants (40HNMA, 13HMF). The materials were tested in the as-received state, however, in the case of the 13HMF steel also after different periods of exploitation (76000h and 144000h at elevated temperature (813K) under internal pressure (14 bars)). Destructive and non-destructive testing methods were applied to assess material degradation. As destructive methods the standard tension tests were carried out after every kind of prestraining. Subsequently, an evolution of the selected tension parameters were taken into account for damage identification. In order to assess a damage development during the creep and plastic deformation the tests for both steels were interrupted for a range of the selected strain magnitudes. The ultrasonic and magnetic techniques were used as the non-destructive methods for damage evaluation. The last step of the experimental programme contained microscopic observations. A good correlation of mechanical and selected non-destructive parameters identifying damage was achieved for the tested steels. It gives very promising tool for degradation assessments appearing in pipelines at power stations.

Barkhausen noise, microstructure, hardness, ultimate tensile strength, structural steels

structural components, static loading, markers, displacement, deflection, DIC

mini-specimen CT, fracture toughness, CTOD, fatigue pre-cracking, notch, fracture, parent material, weld, HAZ

mini-próbka, parametry mechaniczne, rozciąganie, skręcanie, pękanie

The paper reports results of tests focused on determination of kinematic properties of components under cyclic loading. DIC system called 5M PONTOS was employed to follow variations of displacement and velocity versus time. It was conducted by a use of markers stuck on selected sections of components tested. Results are presented in 2D and 3D coordinate systems expressing behaviour of elements such as: car engine, boat frame and mechanical coupling device. These data enable to capture weak and strong sections of the component tested at various loading conditions.

digital image correlation system, cyclic loading, PONTOS, motion, displacement, 3D coordinate system

The paper shows how modern contactless Digital Image Correlation (DIC) method can be implemented for examination of material behaviour under various types of loading. DIC method was used to evaluate material straining under monotonic tension conducted by the use of flat specimens having artificial defects in the form of U and V notches. This technique was also examined during capturing of strain distribution in dynamic tests on Split Hopkinson Pressure Bar. On the basis of DIC results the strain maps at various stages of material deformation were elaborated in order to indicate characteristic features of a material behaviour. It enabled an analysis of damage zone evolution up to specimen fracture.

Digital Image Correlation, specimen, monotonic tension, Split Hopkinson Pressure Bar, strain maps

The paper presents selected cruciform specimens recommended for static and fatigue tests. Guidelines for cruciform specimens designing and optimization are presented. Numerical data of FEA analysis of Kelly's cruciform specimen in 3D coordinate systems are shown. Various types of cruciform testing machines and their advantages and disadvantages are discussed. The project of the cruciform specimen for examination of material behaviour under static and cyclic loading types is proposed.

cruciform specimen, biaxial stress state, specimen optimization, static test, fatigue test, FEA, effective stress

The paper presents results of numerical and experimental investigations conducted in order to determine an influence of notch type on material behaviour under monotonic tension. Two kinds of specimens having U and V notches were applied. Digital image correlation system was used to detect variations of strain/stress state components from beginning of the test up to fracture of the material in question. Assessments of the results enabled identification of stress concentrations in tips of notches. A comparison of tensile characteristics of unnotched and notched specimens exhibited a great reduction of the yield point independently of the geometrical discontinuities applied. In the case of V-notched specimen 50% lowering of elongation was observed.

stress concentration, stress distribution, notches, tensile curve, digital image correlation

Wpływ karbów jest określany zarówno od strony badań teoretycznych, jak i doświadczalnych. Pierwsze z nich umożliwiają przewidywanie zniszczenia na podstawie analizy zmian wartości współczynnika koncentracji naprężenia (WKN) i pozwalają zilustrować jego zmiany w zależności od geometrii karbu. Z kolei w eksperymentach próbuje się określać, jakie znaczenie na otrzymywane wyniki ma rodzaj próbki. Najczęściej stosowane są w tych badaniach próbki rurkowe lub płaskie. W strefie pomiarowej nacinane są karby o różnym kształcie i wymiarach [1]. Uzyskiwane rezultaty z badań wskazują na 50% obniżenie liczby cykli do zainicjowania pęknięcia wraz ze wzrostem promienia karbu od 0 do 6.35mm [2]. Podobny efekt uzyskano również przy wzroście wartości WKN od 1 do 2.833 [1, 3]. Wyniki tego rodzaju nie ujawniają jednak wystarczająco wpływu nieciągłości geometrycznych w bliskim otoczeniu karbu. Rozwiązanie tego problemu może nastąpić poprzez wykorzystanie nowoczesnej techniki pomiarowej DIC (cyfrowa korelacja obrazu). Dlatego też głównym celem pracy było określenie wpływu karbów na zachowanie materiału w teście rozciągania do zniszczenia przy użyciu wymienionej techniki pomiarowej

The effects commonly taking place during proportional and non - proportional (circle and square) types of loading were identified experimentally. Experimental results of tests under cyclic loading assisted by monotonic deformation are compared to their predictions using the Mróz - Maciejewski model

The paper reports the experimental data of tests on the 10H2M steel, carried out under complex loading being combination of monotonic tension and cyclic torsion. Two types of torsion cycles were applied, i.e.: symmetrical and asymmetrical, having four blocks of different shear strain amplitude within a range from ±0.1% to ±0.8%,. All tests were conducted using the tubular specimens at room temperature. The main aim of the experimental procedure was focused on examination of axial stress variations due to torsion cycles of step increasing strain amplitude. An analysis of the results showed a significant reduction of the tensile stress. This effect became stronger when the torsion strain amplitude was increased andit achieved 85% stress drop at highest strain amplitude considered in comparison to the standard tensile characteristic.

complex loading, biaxial stress state, stress reduction, tensile stress, shear stress, tubular specimen