Institute of Fundamental Technological Research

Experimental and numerical tests of surface plastic deformation generated under different strain rates were performed. Deformations were introduced by both classical Brinell and laser pulse hardness tests. An Nd:YAG laser with a wavelength of 1064 nm and a laser pulse time length of 10 ns was used to generated a shock wave to induce local plastic deformation on the material surface. The laser pulse induces a repeatable plastic deformation of a surface without thermal effects on the surfaces. Based on imprint geometry, the dynamic hardness of materials was evaluated at a strain rate of the order 107 s-1. Numerical analyses carried out included quasi-static and dynamic Brinell hardness tests and laser pulse interactions with materials. The Rusinek-Klepaczko constitutive model applied in the calculations allows the prediction of the mechanical characteristics at a strain range strain range from 10 to 4 s-1 to 107 s-1. Numerical and experimental results from the surface plastic deformations show close agreement.

laser pulse, dynamic hardness, plastic deformations, metals

The paper presents result of experimental and numerical tests of plastic deformation of austenitic steel generated by a nanosecond laser pulse. The shock wave generated by the laser pulse was used to induce local plastic deformation of the material. The study examined the possibility of using the process to develop a laser forming of materials under ultra-high strain rate. It has been shown that the laser pulse with intensity 2.5 GW/cm2 induces a repeatable plastic deformation of commercially available 304 steel without thermal effects on the surface

Laser pulse, Plastic deformations, Microstructure, Numerical simulations

Fatigue loading induces a microstructure evolution leading to the change of macroscopically observed mechanical behavior of a dual phase DP500 steel. It was assumed that stress–strain characteristic of a pre-fatigued material may be determined using constitutive equation taking into account damage parameter. To estimate development of the fatigue damage in specimen a variation of the inelastic strain component was applied.

The flat „dog-bone” specimens were initially loaded using stress controlled cycles. When the strain reached a given value the fatigue process was stopped. Subsequently, the specimens with introduced fatigue damage were subjected to tensile tests. Next, the Johnson-Cook's constitutive equation was calibrated separately for each pre-fatigue case. Finally, a new constitutive relationship, based on the Johnson-Cook's model was proposed. It reflects the hardening and softening effects by taking into account both a change in the dislocation structure and development of fatigue microdamage. Proposed model shows a very good agreement with experimental data.

Constitutive model, Dual-phase steel, Fatigue, Stress–strain curve, Fatigue damage, Inelastic strain

Taylor impact tests in the classic and symmetric configurations were applied to analyse the development of plastic deformation and damage in Al-6082-T6 rods. Deformation histories during impact were recorded using high-speed photography, while internal axial damage was identified using metallography. The axial damage observed during the symmetric test were initiated during stress triaxiality peaks under tensile loading conditions. Variations of the stress state are the result of superimposed lateral mechanical waves reflected from the perimeter of the specimen. The fracture strain decreases with the increase of the stress triaxiality; it is thus possible to initiate damage at relatively low strain values under high-stress triaxiality values. During classic Taylor test because of the deflection of the elastic steel anvil in the rod on anvil test, the oscillations are smaller and quickly damped in comparison to the rod on rod experiment. Therefore, the initiation of axial damage is impossible. The cracks on the specimen edge are due to tensile loadings. For both the symmetric and classic Taylor tests, the damage conditions are comparable, i.e., a stable increase of strain combined with tensile loadings.

Taylor impact, Numerical modelling, High-speed photography, Damage initiation, Constitutive relation

The analysis involved subjecting DP 500 steel to pre-fatigue loads, and then tension at high strain rates using Hopkinson bar. Digital image correlation method was used to investigate how the pre-fatigue loads change the strains’ distribution on the surface of the sample subjected to tension. The analysis involved both films recorded at low rates of deformation (1.0 × 10−2 s−1) using ARAMIS system and the images captured with a high-speed camera during dynamic deformations with a Hopkinson bar (6.0 × 102 s−1). It was noted, based on the micro-structural analysis, that pre-fatigue loads cause the formation of micro-damages in the examined material. Thus, macroscopically observed stress–strain characteristic as well as Huber–Mises substitute strains’ distribution determined locally by the image correlation method is also subject to changes. The observed effects include the following: reduction of deformation corresponding to the tensile strength, decrease in elongation at break, and increase in yield limit and tensile strength. The observed effects are intensified with an increased stress value and pre-fatigue cycles’ number. Furthermore, these phenomena are more intensive in the conditions of dynamic deformation.

Hopkinson bar, fatigue, viscoplastic response, damage, stress–strain, tensile, high strain rate

This study analyses the influence of fatigue loading on the residual tensile properties of AISI 1045 steel. The fatigue tests were carried out under stress-controlled tensile loadings at a stress ratio equal to 0. The maximum applied stresses were within the range from 550 MPa to 790 MPa. An analysis of ratcheting strain and plastic strain amplitude evolution due to fatigue loading was performed on the experimental data. In the next stage of this study, the initial fatigue loadings were introduced. Two maximum stresses, 550 MPa and 750 MPa, and three cycle lengths, 25%, 50% and 75% of the total number of cycles required to fracture the material at a given stress, were used. The pre-fatigued specimens were subjected to tensile testing at strain rates from 10−4 to 100 s−1. A large number of fatigue cycles, equal to 75% of the fatigue life, induces material softening as well as a drop in elongation and a reduction of area. Pre-fatigue at maximum stress equal to 550 MPa results in the increase of the elastic limit and offset yield point as well. Both parameters reach almost constant value after number of cycles equal to 25 % of the fatigue life. The further increase in the number of cycles does not affect elastic limit and offset yield point in a clearly visible way. The increase of maximum stress of the initial fatigue loadings up to 750 MPa induces similar but stronger effect i.e. increase and stabilization of elastic limit and offset yield point values, however decrease of both parameters value is observed at large number of pre-fatigue cycles corresponding to 75% of the fatigue life.

Pre-fatigue, Cumulative fatigue damage, Stress–strain, Tensile test, Strain rates

The results of energy absorbing analysis of VP159 austenitic steel and LH556 cast alloy were presented in this article. The assessment was carried out on the basis of drop-weight tower perforation test at impact energy equal to 500J and striker velocity equal to 12,5 m/s. Moreover, the basic mechanical properties of both tested materials were estimated in order to calibrate coefficients of the Johnson-Cook visco-plasticity model and Johnson-Cook damage initialization criterion as well. Subsequently, both models were applied for the finite element method simulation of perforation process. The reasonable agreement between measured and calculated shape of energy absorption curves were obtained for steel and cast alloy as well.

Energy absorption, austenitic steel, cast alloy, constitutive modeling, damage initiation criterion

In this work, we focused on investigations of mechanical properties of SiNx and diamond-like carbon thin films deposited by plasma-enhanced chemical vapour deposition method for application in optical devices or solar cells. Mechanical properties of thin films deposited on clean and oxidized silicon substrates were determined by nanoindentation. The main difficulty with the characterization of thin films using nanoindentation method is related to the influence of the substrate on the measured properties of thin layers. We proposed a method to determine the mechanical properties (hardness and Young's modulus) of thin films in single-layer/substrate or double-layer/substrate system through combining the finite element method, nanoindentation experiments and numerical simulations. In this study, a three-dimensional numerical model of nanoindentation tests performed with Vickers diamond indenter was examined to determine the stress distributions during measurement with various maximum loads. The hardness and Young's modulus of the examined layers were determined using two types of procedures, depending on the von Mises equivalent stress distribution obtained at the maximum load. If the size of an elastically deformed region was sufficiently small compared with the thickness of the measured layers, we applied a standard method of measuring at the depth equal to 10% of the layer thickness; otherwise, an approximation method was used to reduce the substrate influence.

silicon nitride, DLC, PECVD, mechanical properties, nanoindentation, FEM

fatigue, metals and alloys, deformation and fracture, cumulative fatigue damage

The application of an extended Rusinek–Klepaczko constitutive equation to predict the mechanical response of 6082-T6 aluminum under the Taylor impact test conditions was presented in this article. The numerical results obtained in the study were verified through a comparison with the experimental data extracted from the Taylor anvil-on-rod impact experiments. It was concluded that the extended Rusinek–Klepaczko constitutive model predicts the behavior of the tested aluminum alloy under applied loading conditions with satisfactory accuracy. Moreover, it was found that the plastic wave phenomenon in this material is very limited and that there was no region of constant plastic wave velocity. Strain rates up to 1.6 × 104 s−1 were recorded during the Taylor impact experiments; therefore, this value may be set as the upper limit of the extended Rusinek–Klepaczko model for the alloy, which was validated with the anvil-on-rod experiment.

Taylor test, split Hopkinson pressure bar, direct impact compression test, 6082-T6 aluminum alloy, plastic wave propagation

This paper presents the assembly of the miniaturised direct impact compression test method (MDICT) developed at the Institute of Fundamental Technological Research at the Polish Academy of Sciences (IFTR PAS). Additionally, this method was used to investigate the mechanical properties of tantalum at the strain rate of 8×10^5 s−1.To analyse the phenomena occurring during the tests, a numerical model of the testing stand was developed and validated. The finite element (FEM) model was expanded to estimate the sources of error achieved in the results using the analytical methods. The effects related to friction, inertia, specimen ratio, adiabatic heating, stress equilibration and strain rate on the stress-strain characteristic observed before and after the analytical correction were discussed.

miaturised Hopkinson bar, tantalum, high strain rates, direct impact, finite element method

In this paper, a new method for assessing the accuracy of a constitutive model is proposed. The method uses perforation test done by drop weight tower. The assessment is carried out by comparison of striker velocity curve obtained using experiment and FEM simulation. In order to validate proposed method the various constitutive equations were applied i.e. Johnson-Cook, Zerilli-Armstrong and the extended Rusinek-Klepaczko to model mechanical behaviour of X4CrMnN16-12 austenitic steel. The steel was characterized at wide range of strain and strain rates using servo-hydraulic testing machine and split Hopkinson pressure bar. The relative error calculated as a difference between measured and constitutive model based stress-strain curve was applied as a reference data (classic approach). Subsequently, it was compared with relative error determined on the basis of experimental and FEM calculated striker velocity (new approach). A good correlation between classic and a new method was found. Moreover, a new method of error assessment enables to validate constitutive equation in a wide range of strain rates and temperatures on the basis of a single experiment.

plastic behaviour, fracture properties, constitutive modeling, perforation, austenitic steel

The paper presents the results of the analysis of the striker shape impact on the shape of the mechanical elastic wave generated in the Hopkinson bar. The influence of the tensometer amplifier bandwidth on the stress-strain characteristics obtained in this method was analyzed too. For the purposes of analyzing under the computing environment ABAQUS / Explicit the test bench model was created, and then the analysis of the process of dynamic deformation of the specimen with specific mechanical parameters was carried out. Based on those tests, it was found that the geometry of the end of the striker has an effect on the form of the loading wave and the spectral width of the signal of that wave. Reduction of the striker end diameter reduces unwanted oscillations, however, adversely affects the time of strain rate stabilization. It was determined for the assumed test bench configuration that a tensometric measurement system with a bandwidth equal to 50 kHz is sufficient

Hopkinson bar, tensometer bridge, amplifier bandwidth, strain measurement

This paper presents the proposed new model of energy consumption by electric car, determined based on the course of the velocity. The model has been verified by comparing with the results obtained on a chassis dynamometer under the conditions described in the New European Driving Cycle (NEDC). A good compliance with both momentary and total electrical energy consumption while driving was obtained. The model can be used to analyze the distribution of charging stations locations that will allow quick charging or replacement of traction batteries to extend the range of electric cars.

electric car, energy consumption, traction batteries, chassis dynamometer

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

The article presents results of application of Rusinek-Klepaczko (RK) constitutive equation for the purposes of modelling of mechanical behaviour of four grades of structural steels. In order to calibrate the RK model a series of compression tests at wide range of strain rates were carried out using two testing stands: servo-hydraulic machine and split Hopkinson bar. The results were analysed to determine influence of temperature and strain rate on visco-plastic response of tested steels. It was concluded that at low temperatures the thermally activated mechanisms of plastic deformation results in the strong strain rate hardening effects, whereas at high temperatures they are limited.

Structural steels, Rusinek-Klepaczko constitutive model, Hopkinson bar, High strain rates

Around 20% of CO2 emitted as a result of human activity on Earth comes from transportation. One of the ideas, which lead to diminishing of the greenhouse gases e mission, is reducing of fuel consumption. It may be achieved by introducing a new powertrain solutions as well as lowering overall vehicle weight. The reduction of vehicle weight may be obtained by both a new design of part and structures and application of a new materials i.e. aluminium alloys. It has to be emphasised that weight reduction is very important for combustion engine driven vehicles and electric driven vehicles as well. Mass lowering is especially desirable in the case of electric vehicles because they typically have a very narrow operational range usually lower than 200 km. Therefore even small weight reduction de creases energy consumption of EV and as a consequence increases its range, which is a crucial parameter for users.
The results presented in this article were focused on high strength aluminium alloys of 6082-T6 and 7075-T6 types. Applying of those materials enables mass lowering of structures up to 50%, maintaining original functionality. Moreover, aluminium alloys may be also used in energy absorbing structures. The goal of tests was to obtain data required in FE analysis. In order to simulate dynamic phenomenon i.e. vehicle crash investigation of the stress-strain curves of alloys were carried out at wide range of strain rates using Hopkinson bar.

road transport, simulation, combustion engines, air pollution, environmental protection

Praca przedstawia charakterystyki naprężenie-odkształcenie stali austenitycznej VP159 oraz staliwa austenitycznego LH556, o dużej zawartości azotu, przy różnych prędkościach odkształcania. Do badań w zakresie obciążeń statycznych zastosowano serwohydrauliczną maszynę wytrzymałościową, natomiast w zakresie obciążeń dynamicznych metodę pręta Hopkinsona. Otrzymane rezultaty przedstawiono w formie wykresów naprężenia rzeczywistego w funkcji odkształcenia rzeczywistego. Na podstawie statycznej próby rozciągania wyznaczono również podstawowe parametry badanych materiałów, takie jak: E, R0,05, R0,2, Rm. Na podstawie badań stwierdzono, że stal VP159 ma znacznie lepszą ciągliwość niż staliwo LH556, natomiast pozostałe parametry i charakterystyki były zbliżone. Otrzymane wyniki można wykorzystać do wyznaczenia parametrów równań konstytutywnych opisujących termomechaniczne właściwości materiałów na potrzeby symulacji komputerowych.

mechanika, pręt Hopkinsona, duże prędkości odkształcania, stal wysokoazotowa, charakterystyka naprężenie-odkształcenie

This work presents the impact resistance results of investigation on the VP159 high nitrogen steel. The tests were carried out using the Instron impact system at the projectile velocity equal to 12,5 m/s. The experimental results were compared to the FE predictions. The Rusinek-Klepaczko constitutive model was applied to describe mechanical response of tested material. It was concluded that the FE results were in a good agreement with the experiment.

This work compares the thermomechanical behavior of TiNi shape memory alloy subjected to the compression test performed under various strain rates. The mechanical characteristics of the material were elaborated. The specimen temperature changes related to the exothermic martensitic forward and endothermic reverse transformation were measured in a contact-less manner by a very fast and sensitive infrared camera. It has been found that in this experimental conditions the stress-induced transformation and reorientation processes occurred homogeneously, since the temperature distribution observed on the specimen surface was uniform. The obtained temperature variation depends on the strain rate applied. At the higher strain rate the higher temperature changes were obtained, because the heat flow to the surroundings was lower and the process was closer to adiabatic conditions. The temperature changes influence significantly the SMA stress-strain curves and their mechanical properties.

shape memory alloy, various strain rates, compression tests, exothermic martensitic forward, endothermic reverse transformation, fast and sensitive infrared camera

The paper presents the results of tests on polycrystalline tantalum at very high strain rates (7.5x104 s-1). The measurements were carried out using miniaturized Direct Impact Compression Test (DICT) method. The transmitting bar diameter was 3mm, and the tested specimens were cylindrical shape of 1.5 mm diameter and 0.55 mm thickness. A numerical model of the testing stand was developed in the ABAQUS environment to trace the phenomena occurring during specimen deformation and to evaluate their influence on the final result. The test stand dimensions and the test parameters used in the calculations were this same as for DICT experiments. The results of computer simulations demonstrated good agreement with experimental results, which proves that the Finite Element Method (FEM) reproduces well the behavior of the stand and can be applied in analyses performed to find the reasons of errors in plastic stress flow measurements.

Direct Impact Compression Tests, Tantalum, high strain rates, compression tests, Hopkinson bar

In this paper original experimental methodologies of dynamic plastic behavior of various structural materials in a wide range of strain rates up to 10 5 s - 1, and at selected temperatures are presented. Identification of constitutive models and their verification are also included