Tension-compression Tests Research Articles

Thermal and athermal contributions to the flow stress of martensite

Recent theories consider as-quenched martensite as a composite which strain hardens by the gradual yielding of constituents. An underlying hypothesis is that hardening comes primarily from athermal hardening contributions. In this contribution, we conducted strain-rate jump and tension-compression tests to quantify the athermal and kinematic hardening contributions in martensite. It is shown that athermal hardening accounts for ~75% of the total strength of as-quenched martensite. The magnitudes of athermal and kinematic hardening decrease as a function of tempering. A correlation between the athermal and kinematic hardening contributions is identified and shown to be independent of the chemistry and tempering conditions examined in this work.

Graphene Size and Morphology: Peculiar Effects on Damping Properties of Polymer Nanocomposites

Nanomaterials with their extremely high free surfaces can effectively augment damping in nanocomposites via frictional sliding along the interface of nanomaterials and a matrix. Despite this potential, existing state of knowledge about the damping behavior of graphene reinforced nanocomposites is at an embryonic stage. In particular, it is not clear how various morphological parameters of graphene contribute to damping. We aim to reveal the mechanical damping behavior of graphene-reinforced polymer nanocomposites as a function of the surface morphology of graphene nanoplatelets through combined experiments and continuum modeling. The vibrational damping behavior of graphene nanocomposites was studied via dynamic mechanical analysis via cycling tension-compression tests. Two graphene types, “single-layer graphene” (SLG) and “graphene nanoplatelets” (GNP), with different aspect ratios in polystyrene (PS) matrix were used. We developed a micromechanical model which relates damping in nanocomposites to filler-matrix frictional sliding. The experimental work demonstrated that the addition of GNP will increase the damping properties of the nanocomposites by up to ~70%. The model predictions for PS-GNP were in good agreement with experimental data. However, contrary to the model predictions, the damping coefficient of nanocomposites with lower aspect ratio particles (PS-SLG) was lower than PS-GNP. Further experimental studies showed that the surface roughness of the SLG (owed to their small thickness) has a negative effect on damping properties as they delay interfacial debonding and frictional sliding. Flat (less rough) graphene triggers intrinsic friction mechanism earlier and may be more beneficial to enhance damping. Surface undulation of the nanoparticles, which can happen for atomically thin particles, will delay damping.

Fatigue response up to 109 cycles of a structural epoxy adhesive

AbstractIn the present paper, the very‐high‐cycle fatigue (VHCF) response of a structural adhesive used for automotive applications, Betaforce 4600G modified with microspheres, has been experimentally assessed. Ultrasonic fully reversed tension–compression tests up to 109 cycles have been carried out with the testing machine developed by the authors on adhesives without macroscopic defects and on adhesives with artificial defects, inserted during the butt‐joint preparation. Fracture surfaces have been observed with the optical microscope and the P‐S‐N curves estimated. Experimental results have shown that defect location significantly affects the VHCF strength and fracture surfaces exhibit a peculiar morphology with three distinct characteristic regions.

Using Fatigue Characteristics to Analyse Test Results for 16Mo3 Steel under Tension-Compression and Oscillatory Bending Conditions

In this study, 16Mo3 steel was analysed for fatigue tests under tension-compression and oscillatory bending conditions. The analysis involved a comparison of fatigue test results obtained using the Manson-Coffin-Basquin, Langer and Kandil models and the models proposed by Kurek-Łagoda. It was observed that it is possible to substitute the basic tension-compression test performed in large testing machines with oscillatory bending tests carried out on a simple, modern test stand. The tests were performed under oscillatory bending on a prototype machine. The testing of 16Mo3 steel proved that the best-known Mason-Coffin-Basquin fatigue characteristic describes the results of all of the experimental tests very well, but the model can only be used when it is possible to divide strains into elastic and plastic components. It should be emphasised here that there is no such possibility in the case of tests performed under oscillatory bending conditions. It was proven that the proposed test method can substitute the tension-compression test very well and be a much more cost efficient way to obtain LCF material fatigue properties.

Material characterisation of additively manufactured elastomers at different strain rates and build orientations

Material jetting, particularly PolyJet technology, is an additive manufacturing (AM) process which has introduced novel flexible elastomers used in bio-inspired soft robots, compliant structures and dampers. Finite Element Analysis (FEA) is a key tool for the development of such applications, which requires comprehensive material characterisation utilising advanced material models. However, in contrast to conventional rubbers, PolyJet elastomers have been less explored leading to a few material models with various limitations in fidelity. Therefore, one aim of this study was to characterise the mechanical response of the latest PolyJet elastomers, Agilus30 (A30) and Tango+ (T+), under large strain tension-compression and time-dependent high-frequency/relaxation loadings. Another aim was to calibrate a visco-hyperelastic material model to accurately predict these responses. Tensile, compressive, cyclic, dynamic mechanical analysis (DMA) and stress relaxation tests were carried out on pristine A30 and T+ samples. Quasi-static tension-compression tests were used to calibrate a 3-term Ogden hyperelastic model. Stress relaxation and DMA results were combined to determine the constants of a 5-term Prony series across a large window of relaxation time (10 μs–100 s). A numerical time-stepping scheme was employed to predict the visco-hyperelastic response of the 3D-printed elastomers at large strains and different strain rates. In addition, the anisotropy in the elastomers, which stemmed from build orientation, was explored. Highly nonlinear stress-strain relationships were observed in both elastomers, with a strong dependency on strain rate. Relaxation tests revealed that A30 and T+ elastomers relax to 50 % and 70 % of their peak stress values respectively in less than 20 s. The effect of orientation on the loading response was most pronounced with prints along the Z-direction, particularly at large strains and lower strain rates. Moreover, the visco-hyperelastic material model accurately predicted the large strain and time-dependent behaviour of both elastomers. Our findings will allow for the development of more accurate computational models of 3D-printed elastomers, which can be utilised for computer-aided design in novel applications requiring flexible or rate-sensitive AM materials.

Fatigue criteria for short fiber-reinforced thermoplastic validated over various fiber orientations, load ratios and environmental conditions

Design of reinforced plastic parts against fatigue failure has become a serious issue these last few years for increasing engineering field applications. This is indeed a complex problem due to the strong anisotropy induced by the orientation of the fibers during the injection process and to the non-linear dissipative behavior of the matrix. This generates strong influences of numerous parameters (fiber orientation, environment, strain rate, load ratio, …), which complicates both the description of the constitutive response and the definition of a robust and efficient fatigue criterion. This paper presents a very wide fatigue database (480 tension-compression tests) obtained on Polyamide 66 reinforced with 50% of glass fibers (PA66 GF50), for an extended range of load ratios (from −0.5 to 0.7), three orientations from the injection direction (0°, 45°, 90°) and two environmental conditions (50% humidity ratio and 80 °C, 80% humidity ratio and 23 °C). Beyond these experimental results, the goal of this paper is to compare the ability of numerous fatigue criteria to provide a robust description of the fatigue database, possibly with a unified set of parameters. Classical models as well as very recent ones are discussed and two variants of a new fatigue criterion are finally defined. This criterion is able to describe very accurately the full database with only four parameters. Finally, a focus is given to determine the minimal amount of experimental data needed to obtain a reliable description of the fatigue results, on the full ranges of load ratios, orientations and environmental conditions.

Toughened carbon-fiber reinforced epoxy via isophorone diisocyanate amine surface modification

Surface modification of a carbon-fiber reinforced epoxy (CF/E) via isophorone diisocyanate amine (IDA) is investigated. The covalently bonded IDA, engendering a microscopically thin layer (2 μm–50 μm wide), is an exchange chemical reaction after topically spraying polyurea moieties (isocyanate and amine groups) to curing epoxy that is composed of amine and epoxide groups reacting for tc hours (h). Quasi-static nanoindentation, uniaxial tension and uniaxial compression tests reveal that the chemical bond feature of the tunable IDA surface, conceived at low tc, markedly improves damage tolerance in brittle CF/E by significantly supplementing the energy-release rate (fracture toughness). Compression tests revealed that energy absorption and deflection ductility of IDA-modified CF/E, i.e., C-IDA, and prepared at tc = 0 h, are two and five times greater relative to C-IDA at tc = 0.5 h. Tension tests revealed that energy absorption and deflection ductility of C-IDA at tc = 0 h are 150% and 50% greater than C-IDA at tc = 24 h. Micromechanical properties of the IDA reaction include a uniquely distributed reduced elastic modulus (Er), bounded by moduli of pure epoxy and pure polyurea (overspray). The results, in concert with atomic force microscopy (AFM) and non-negative matrix factorization (NMF) results, validate a link between IDA chemistry and mechanical energy transferability. Manifested as damage localization, fractograph analysis also confirms existence of the link, where bridging of individual damage events in CF/E is markedly reduced.

Modeling the Residual Stresses Induced in the Metastable Austenitic Stainless Steel Disc Springs manufactured by Incremental Sheet Forming by a Combined Hardening Model with Phase Transformation

A numerical model for predicting the beneficial residual stress induced in metastable austenitic stainless steel (MASS) disc springs through incremental sheet forming (ISF) is developed. An important input for the numerical model is the phase-specific flow curves of the MASS constituents, i.e., austenite γ and martensite α phase. These curves are determined by using an available CP-FEM framework. The cyclic plasticity effects introduced by the bending/unbending deformation mechanism of the ISF are modeled by using a combined non-linear isotropic/kinematic hardening model. The kinetics of the strain-induced martensite transformation is modeled by using the Olson-Cohen model, whereas the stresses in the whole material are approximated by a mixture rule. The combined non-linear isotropic/kinematic hardening along with Olson-Cohen model and the mixture rule is integrated as a user-material routine (UMAT). The model parameters are calibrated by tensile tests with online Feritscope measurements and tension-compression tests. Afterward, the incremental forming simulations of disc spring manufacturing are performed and the numerically determined residual stress values are compared to the experimental values. The comparison indicates a good match. Hence, the developed numerical strategy provides accurate residual stresses prediction and can be utilized to design the disc spring properties through adjusting residual stresses, which is possible by varying process parameters of the ISF process.

The influence of the kinematic hardening on the FEM simulation of Tension Levelling Process

Tension levelling is used in the steel industry to remove shape defects present in cold rolled strip. This technology is increasingly being employed by steel makers to level AHSS steels, because conventional roll levelers are not able to correct explicit local errors like wavy edges and central buckles. In this study, the influence the hardening law has on the simulation of tension levelling processes using FEM is studied. Tension-compression tests have been performed in a DP1000 steel using several reversal cycles and a mixed nonlinear kinematic hardening law has been fitted to the experimental data using different amount of backstress tensors. It is observed that numerical results are influenced by the introduced hardening law and thus is an important input when simulating the tension levelling process.

Mechanical Splices for Seismic Retrofitting of Concrete Structures

As an alternative to lap splicing, mechanical splices can be used for retrofit purposes. They are generally most economical than traditional lap splices when available spacing or length makes laps difficult to utilize. Mechanical splices are frequently used in new construction. However, their use is limited and not practical for use in retrofitted structures. However, if the bars to be joined do not need to be threaded in order to be connected with a special mechanical splice, such mechanical splices can be useful. It is presented a proposal of using two types of mechanical splices for retrofit purposes. Cycle Tension and cycle tension-compression tests are presented and discussed. It was found that mechanical splices are suitable and have acceptable response under seismic loads.

Springback Evaluation of Tailor Welded Blanks at V-die Bending made of DP Steels

This study presents the experimental results and the comparison of different analytical models for springback evaluation of bent thin sheets. Three types of advanced high strength steels (from the group of dual phase steels, namely DP600, DP800 and DP1000) and a mild steel (DC04) were used to investigate the sheet profile after rectangular V-die bending. Uniaxial tension-compression tests were also carried out formerly to lay the basis of the precise theoretical examinations. Striving to consider all possible circumstances, the change of the elastic modulus with the increase of the plastic strain, as well as plane strain state with the corresponding yield stress were assumed during the springback prediction. In certain cases, the effect of the sheet thickness variation was also taken into account. In many practical stampings, these variables can be at least partially neglected, but the presented models also can lead to poor accuracy, even though they are more complicated. According to our experiences, both the circular approximation and the moment-equilibrium based general formulae predict under the measured springback angles, but the punctuality can be developed by precise material behavior modelling. The phenomenological approach extended with fitting parameters gives the most accurate estimation obviously, but the physical meaning of the added parameters remain a question. The uncertainty is being more enhanced at the tailor-welded blanks (TWBs) where the interaction of the components should not be negligible as well, i.e. a subsequent variable, namely the distance from the weld line comes into the focus. Laser beam welding was applied to joint each DP steels to the mild steel component and then the sheets with different widths were bent perpendicular to the weld line. Due to the doubled effect on the deforming or restraining action of the different sides, the final shape and thus the curvature shift towards the weld line from the blank’s edge. It means that new viewpoints need to consider at the analytical springback evaluation of TWBs.

Characterization of kinematic hardening with a hydraulic bulge test

The increase of the mapping accuracy in numerical simulations of sheet metal forming processes is an important field of research today. In this context, the modelling of the kinematic hardening plays a major role when it comes to nonlinear strain paths during the forming process. The kinematic hardening leads, beside other effects, to a lower increase of the hardening after a change of the linear strain path. Characterization of the Bauschinger coefficient, an indicator of the portion of kinematic hardening, is normally done with cyclic tension-compression tests. The testing setup is quite challenging in the strain measurement and the specimen handling due to the small geometry and the risk of buckling during compression. Thus, a hydraulic bulge test with an optimized geometry is used for the characterization of the kinematic hardening with a strain path change for the materials DC06 and DP600. According to literature, DC06 has no significant kinematic hardening, while the high strength steel DP600 is sensitive to this hardening mechanism. The strain path change is realized by a secondary element in the die. In the beginning of the test, a conventional circular die induces an equi-biaxial strain. After this preforming step, an elliptical geometry is used to induce plane strain in the specimen. The resulting strain path changes from equi-biaxial to plane strain. The flow curves out of the experiment show the kinematic hardening effect after the strain path change for the DP600 while no change is observable for the DC06. Numerical simulation with the identified kinematic factor should lead to a better mapping accuracy regarding the springback behavior.

Influence of Aggregate–Binder Adhesion on Fatigue Life of Asphalt Mixtures

Abstract The adhesiveness between aggregate and asphalt binder is believed to affect the life cycle of asphalt pavements, mainly in the presence of water. One of the most common asphalt pavement distresses is fatigue cracking. The objective of this article is to investigate the relationship between adhesion properties and fatigue life of asphalt mixtures. The asphalt bond strength test was used to measure adhesion (pull-off tensile strength) at two different moisture conditioning states: unconditioned (or dry) and conditioned in distilled water for 24 h at 40°C. The test consists of measuring the pull-off pressure required to break an aggregate–binder interface, called the pull-off tensile strength. For the fatigue damage characterization of the mixtures, controlled crosshead sinusoidal tension-compression tests were used, associated with the Simplified Viscoelastic Continuum Damage modeling protocol. Four asphalt mixtures were investigated. They share the same aggregate gradation but differ in aggregate source (two different sources) and the presence or absence of an anti-stripping agent. The mixture with pure asphalt binder showed higher values of pull-off tensile strength than mixtures with asphalt binder doped by an anti-stripping agent. However, the analysis of the pull-off tensile strength ratio (comparison between unconditioned and moisture-conditioned specimens) showed that the addition of anti-stripping agent provided significant moisture damage resistance in the aggregate–binder interface. Results also show that mixtures with asphalt binder modified by anti-stripping agent had higher simulated fatigue life than mixtures with pure asphalt binder. Excellent correlations were obtained between the strain amplitude required to obtain a given @ Nf (strain amplitude @ Nf) with pull-off tensile strength, which confirms that the fatigue life of asphalt mixtures is related to the adhesion between aggregate and asphalt binder.

Parameter Determination and Application Research of Mixed Hardening Model Based on Cyclic Tension-compression Test

Parameter Determination and Application Research of Mixed Hardening Model Based on Cyclic Tension-compression Test

An Identification Method for Anisotropic Plastic Constitutive Parameters of Sheet Metals

In this work, the virtual fields method (VFM) was extended to simultaneously identify the constitutive parameters of Hill 1948 anisotropic yield criterion and nonlinear kinematic hardening models for rolled sheet metals from a low cycle tension-compression test. First, simulations of different specimens under loading were conducted to determine a specific configuration which exhibits both insignificant buckling effect and heterogeneous stress state. Then, the simulated data were utilized to retrieve the target anisotropic constitutive parameters in order to validate the proposed VFM identification scheme. The results show that the input parameters can be satisfactorily regained from the designed tension-compression configuration and the VFM algorithm, verifying the feasibility of using this method to real experiments.

A continuum-based strength criterion for masonry: identification of parameters and validation

This paper is focused on the formulation and verification of an anisotropic continuum-based strength criterion for structural masonry. In the approach followed here, the failure function incorporates a scalar anisotropy parameter whose value depends on the orientation of the principal stress system in relation to preferred material directions. An explicit identification procedure for the material parameters/functions is developed and a numerical study, including a set of simulations of biaxial compression-tension tests for different orientations of bed joints, is conducted to verify the predictive abilities of this criterion. The results are compared with the experimental data of Page (1983). In the last part, 3D finite element analysis of a shaking table test is performed involving reduced scale model of a four storey masonry building subjected to seismic excitation. A linear dynamic analysis is carried out and the plastic admissibility of the resulting stress field is assessed.

A continuum-based strength criterion for masonry: identification of parameters and validation

This paper is focused on the formulation and verification of an anisotropic continuum-based strength criterion for structural masonry. In the approach followed here, the failure function incorporates a scalar anisotropy parameter whose value depends on the orientation of the principal stress system in relation to preferred material directions. An explicit identification procedure for the material parameters/functions is developed and a numerical study, including a set of simulations of biaxial compression-tension tests for different orientations of bed joints, is conducted to verify the predictive abilities of this criterion. The results are compared with the experimental data of Page (1983). In the last part, 3D finite element analysis of a shaking table test is performed involving reduced scale model of a four storey masonry building subjected to seismic excitation. A linear dynamic analysis is carried out and the plastic admissibility of the resulting stress field is assessed.

Temperature Control of a Small Volume-Thermal System in Heating and Cooling Processes with Arduino

An important field of the temperature control is the identification of physical features of materials at a wide range of operating temperatures. This paper presents the design of a temperature controlled thermal system in heating and cooling processes. This system will be used in a tension-compression testing machine. During the tensile experiments, the aim is to keep the inside of the chamber at a desired temperature. The thermal system consists of an isolated metal box, dry resistance, power regulator, thermocouple, air fun, relay, amplifier, microcontroller and computer. For the cooling processes in cryogenic temperatures, the system has also a solenoid valve, DC motor driver and a liquid nitrogen tank. The temperature of the chamber with a small bulk is controlled by a feedback system. This feedback system measures the temperature with a K-type thermocouple and uses a combination of a table-supported PID, P and on-off controllers to compensate the errors between the reference and measured temperatures. In this setup, Arduino is used as a microcontroller because it is simple, inexpensive and easy to program. This card supplies all communication between the computer and the experimental setup by a program written on the MATLAB with Arduino package for real-time applications. According to the experimental results, the temperature of the insulated chamber can be easily maintained between +450 oC and –100 oC. The user defined different temperature profiles were successfully performed on the setup and the outcomes were compared with the mathematical model in the heating and cooling processes. The deviations from the desired temperatures were found to be at an acceptable level for the applications on a tension-compression testing machine.

Modeling the elastic response of polymer foams at finite deformations

Constitutive equations are developed for the elastic behavior of polymer foams under three-dimensional deformations with finite strains. These relations provide an extension of the Danielsson–Parks–Boyce model for a compressible matrix material in a representative volume element, whose volumetric deformation is governed by the specific work of external forces. The mechanical response of foams is described by the governing equations with four adjustable parameters. Two of them are material constants independent of porosity ϕ. The other two coefficients are functions of ϕ, for which simple equations are suggested. The model is applied to the analysis of observations on an extensive number of foams. Good agreement is demonstrated between results of simulation and experimental data in uniaxial tensile tests, compressive tests, and tension-compression tests. Predictions of the model for mechanically induced evolution of the microstructure of foams are in accord with available observations.

Performance testing of asphalt paving mixtures for hot condition using tension–compression test

In this paper, laboratory experiments were conducted on two different asphalt mixes, one using the Marshall mix design method (MMD) and the second using modified Marshall mix design (3M) method. The 3M method is based on the incorporation of two factors, the new asphalt binders (performance grade) and the Superpave gyratory compactor (SGC) as in Superpave mix design method, into the traditional MMD method. All specimens had the same mixtures of aggregate gradation incorporated with two different compaction methods and two asphalt grades using two different classification methods: asphalt cement binder (B60-70) based on the penetration test (Pen system) and PG 70-10 based on performance grade system (PG). However, there were some errors at low temperature (− 25, − 10 °C) and high temperature (54 °C), so these values may be discarded. The tension–compression complex modulus test |E*| is dependent on temperature and loading frequency. Thus, the results of this test will give a more accurate representation of the absolute value of the tension–compression complex modulus test |E*| that defines the elastic properties of a linear viscoelastic material subjected to a sinusoidal loading. In addition, 2-complex modulus (E*) and phase angles (ΦE*) in the test have been measured at temperatures of − 25, − 10, − 5, 10, 25, 35 and 54 °C as well as frequencies of 25, 10, 5, 1, 0.5 and 0.1 Hz. The value of the dynamic modulus reflects the stiffness of the mixture and its resistance to deformation at a designated frequency and temperature. The results show an improvement in the |E*| in the modified 3M mix over the traditional MMD mix. The 3M method using asphalt binder PG 70-10 and gyratory compactor (SGC) as in Superpave mix design method, improves the |E*| of the asphalt mixture in HA climate. As well, intrinsic characteristics related to binder properties, aggregate gradation and compaction method in HA climate have the most significant effect on the predicted |E*|.