Institute of Fundamental Technological Research

The new brake disc was evaluated for microstructure and hardness by the conventional destructive tests and non-destructive Barkhausen noise method (BNM). Ten non-destructive measurements were carried out in different areas of a brake disc, which were then cut out and made into metallographic test samples. Qualitative and quantitative analysis of graphite precipitates was performed to assess their volume in material matrix, anisotropy and size. Subsequently, graphs showing the relationships between selected stereological parameters of graphite precipitates and parameters determined from the RMS envelope of Barkhausen noise were elucidated. Similar relationships between hardness and parameters coming from non-destructive tests were carried out. Magnetic parameters that specified the size of a graphite precipitate was selected. In addition, repeatability studies using BNM were carried out in the areas of the material with the smallest and largest average size of graphite precipitates. A linear relationship between amplitude of BN and length of graphite flakes was found. The paper presents the possibilities of assessing the volume and size of graphite precipitates, as well as cast iron hardness using BNM.

Flake cast iron,Barkhausen noise,Brake disc,Non-destructive testing,Hardness

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 presents an attempt to assess the microstructure and mechanical properties by means of the magnetic Barkhausen noise (MBN) method. The experimental program was supplemented by metallographic examinations and hardness tests. It has been concluded that the MBN method can be used for non-destructive characterization of both single and two-phase steels used in the automotive industry. It was also found that the microstructure of steel can be distinguished using the shape of BN envelope and two magnetic parameters: Ubpp1 and Ug1. On the other hand, the hardness and ultimate tensile strength are described successfully by the Ug1/Ubpp1 parameter.

microstructure, mechanical properties, Barkhausen noise, non-destructive method

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

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

Nonlinear properties of metal matrix composites (MMCs) are studied. The research combines results of loading-unloading tensile tests, microstructural observations and numerical predictions by means of micromechanical mean-field models. AA2124/SiC metal matrix composites with SiC particles, produced by the Aerospace Metal Composites Ltd. (AMC) are investigated. The aluminum matrix is reinforced with 17% and 25% of SiC particles. The best conditions to evaluate the current elastic stiffness modulus have been assessed. Tensile tests were carried out with consecutive unloading loops to obtain actual tensile modulus and study degradation of elastic properties of the composites. The microstructure examination by scanning electron microscopy (SEM) showed a variety of phenomena occurring during composite deformation and possible sources of elastic stiffness reduction and damage evolution have been indicated. Two micromechanical approaches, the incremental Mori–Tanaka (MT) and self-consistent (SC) schemes, are applied to estimate effective properties of the composites. The standard formulations are extended to take into account elasto-plasticity and damage development in the metal phase. The method of direct linearization performed for the tangent or secant stiffness moduli is formulated. Predictions of both approaches are compared with experimental results of tensile tests in the elastic–plastic regime. The question is addressed how to perform the micromechanical modelling if the actual stress–strain curve of metal matrix is unknown.

metal matrix composites, tension with unloadings, damage, microstructure, non-linear effective properties

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

The article presents variations of rms Barkhausen noise envelopes in the medium-carbon steel used in automotive and power industry. The material was subjected to different loading processes: monotonic loading at room temperature, and constant loading at elevated temperature. The first one enforced a plastic deformation, whereas the second one a creep. The changes of Barkhausen signal were analysed using microstructural observations including X-ray measurements. In the second part of the paper, the magnetic structure and pinning effect were illustrated by means of the Lorentz microscopy.

Barkhausen noise, magnetic structure, plastic deformation, creep, dislocation density

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 presents an attempt of application of the acoustic birefringence coefficient for early stage degradation assessment of Inconel 718 nickel superalloy after short-term creep. It is shown that it can serve as a good damage sensitive parameter and, moreover, it can be well correlated with hardness variation.

creep, nickel superalloy, microstructure, pre-deformation, hardness, acoustic birefringence

The paper describes an application of non-destructive volumetric magnetic and ultrasonic techniques for evaluation of the selected mechanical parameter variations of P91 steel having direct influence on its suitability for further use in critical components used in power plants. Two different types of deformation processes were carried out. First, a series of the P91 steel specimens was subjected to creep and second, one to plastic deformation in order to achieve the material with an increasing strain level up to 10%. Subsequently, non-destructive and destructive tests were performed. Magnetic methods based on measurements of magnetoacoustic emission and magnetic hysteresis loop changes as well as the ultrasonic method based on acoustic birefringence measurements, were applied. Finally, the static tensile tests were carried out in order to evaluate the mechanical parameters. It is shown that some relationships between the selected parameters coming from the non-destructive and destructive tests may be formulated.

Creep, Plastic deformation, Acoustic birefringence, Magnetoacoustic emission, Magnetic hysteresis loop

The results of comparative examinations of mechanical behaviour during fatigue loads and microstructure assessment before and after fatigue tests were presented. Composites of aluminium matrix and SiC reinforcement manufactured using the KoBo method were investigated. The combinations of two kinds of fatigue damage mechanisms were observed. The first one governed by cyclic plasticity and related to inelastic strain amplitude changes and the second one expressed in a form of ratcheting based on changes in mean inelastic strain. The higher SiC content the less influence of the fatigue damage mechanisms on material behaviour was observed. Attempts have been made to evaluate an appropriate fatigue damage parameter. However, it still needs further improvements.

fatigue, damage, metal matrix composites, microstructure

In this work, an attempt at determination of mechanical properties by means of a method based on magnetic Barkhausen emission measurements was proposed. The specimens made of P91 steel were subjected to creep or plastic flow which were interrupted after a range of selected time periods in order to achieve specimens with an increasing level of strain. Subsequently, measurements of magnetic Barkhausen emission were carried out, and then static tensile tests were performed in order to check variations of basic mechanical parameters. It is shown that evident relationships between the yield point /ultimate tensile strength and some parameters of the Barkhausen emission exist.

mechanical properties, magnetic Barkhausen effect, plastic strain

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

A consolidation of powders using the KOBO method at elevated temperature was elaborated for production of Al/SiC metal matrix composite (MMC). The observations of the mean strain and inelastic strain range during the force controlled high cycle fatigue (HCF) tests identified the ratcheting mechanism combined with mechanism characterized by cyclic plasticity. Damage parameters were calculated on the basis of strain signal acquisition during fatigue tests. Fatigue properties, creep resistance and life time of Al/SiC MMC were gradually improved with the increase of the SiC particles content. The microstructural observations of the material before and after tests were also performed.

MMC, KOBO method, fatigue, creep, monotonic loading, microstructure, damage

This work presents an attempt to evaluate a stage of mechanical and structural degradation of 40HNMA steel, used for example in automotive industry, by means of non-destructive and destructive methods. The modern ultrasonic and magnetic investigation were mainly applied

stale wysokowytrzymałe, szum Barkhausena, twardość, wytrzymałość na rozciąganie, mikrostruktura

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

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

Creep and fatigue damage was investigated in steels commonly applied in power plants (40HNMA, 13HMF and P91) using destructive and non-destructive methods. In order to assess both types of damage the tests for each kind of steel were interrupted for a range of the selected time periods (creep) and number of cycles (fatigue).

Creep tests under a range of step-increasing tensile stresses were carried out on the AlMg/SiC composites produced by means of the KOBO method. The content of reinforced phase was equal to 2.5, 5, 7.5 and 10%. The AlMg/SiC creep characteristics were compared to those of the Al/SiC composites. Structural assessments of materials in the as-received state and after creep were carried out.

metal-ceramic composites, KOBO method, creep, silicon carbide (SiC)

Fatigue tests and microstructural observations were carried out to perform damage analysis of Al/SiC and AlMg/SiC metal matrix composites ( MMCs ). The materials were manufactured using a KoBo method. Ratcheting was the dominant damage mechanism for Al/SiC and damage parameter on the basis of mean inelastic strain was calculated. For AlMg/SiC, in most cases, cyclic softening followed by hardening during subsequent cycles were noticed. Microstructural observations identified existence of SiC concentrations which influenced the volumetric fraction of defects after fatigue tests

metal matrix composites, fatigue damage, microstructure, KoBo method

In order to elaborate more efficient technological processes enabling a lifetime prolongation of some elements of devices and machines a lot of scientific efforts are focused on searching of the optimal loading combinations. As it has been found by Korbel and Bochniak [1, 2], a significant reduction of tensile or compressive forces in technological processes is possible using twisting moment simultaneously applied. They proposed the so-called KOBO method and successfully applied it to extrusion, forging or rolling processes. Up to now the method was checked for large deformations, what requiredalot of energy. Since the available results of the method validation in the range of small deformations are not sufficiently represented,an experimental programmelimiting maximal strain level below 1% (Fig.1)was elaborated. The strain controlled loading programme enables observation of stress/strain components variation as a function of time (Figs 1 and 2)The loading programme(for the 10H2M steel) contained four subsequent blocks of cyclic shear deformation assisted by tension. As it is illustrated in Fig.2, theaxial stress increases at the beginning of the test (first cyclic strain amplitude). However, for higher cyclic strain amplitudes, its lowering is clearly manifested. Figure 3 shows comparison of tensile characteristics in the case of activated and inactivated torsion cycles. It is seen, that while the torsion cycles were applied a gradual decrease of axial stress can be observed. The maximum drop of it was almost equal to 400 MPa for the highest cyclic strain amplitude used in the programme. The effect of similar order was also achieved for this material tested under monotonic tension and torsion-reverse-torsion cycles ofconstant strain amplitude (0.8%), Fig.4. It means that prior cyclic loading history does not influence a magnitude of the tensile stress drop. A reduction of axial stress due to application of cyclic loading by means of reversible torsion was also observed for other materials, i.e. the P91 steel and M1E copper (Fig.5) [3].

Development of damage due to creep at elevated temperatures and fatigue at room temperature was assessed for power engineering steels using destructive and non-destructive methods. The experimental programme contained also microscopic observations to find feedback between macro- and micro-scopic parameters. Three different power engineering steels were tested, i.e. 40HNMA, 13HMF and P91

Development of damage due to creep at elevated temperatures and fatigue at room temperature was assessed for power engineering steels using destructive and nondestructive methods. The experimental programme contained also microscopic observations to find feedback between macro and microscopic parameters