Biaxial Tension Tests Research Articles

A new strain hardening model for rate-dependent crystal plasticity

This paper presents a crystal plasticity based finite element analysis employing the new microstructure-based strain hardening model recently presented by Saimoto and Van Houtte (2011) [7] to simulate formability and texture evolution in the commercial aluminum alloy 5754. Simulations are performed to compare the predictive capability of the new hardening model against the common work hardening models using a rate-dependent plasticity formulation. The parameters in the numerical models are calibrated using the X-ray data published by Iadicola et al. (2008) [9] for the aluminum sheet alloy 5754. The predictions of the model for balanced biaxial tension and in-plane plane-strain tests are compared against experimental observations presented in Iadicola et al. (2008) [9]. It is concluded that the new model provides the best predictions of the large strain behavior of Aluminum sheet alloy 5754 subjected to various strain paths.

Prediction of anisotropy and hardening for metallic sheets in tension, simple shear and biaxial tension

The mechanical behavior of mild and dual phase steel sheets is investigated at room temperature in quasi-static conditions under different strain paths: uniaxial tension, simple shear and balanced biaxial tension. The aim is to characterize both the anisotropy and the hardening, in order to identify material parameters of constitutive equations able to reproduce the mechanical behavior. In particular, a good description of flow stress levels in tension and shear as well as plastic anisotropy coefficients is expected. Moreover, the Bauschinger effect is investigated with loading–reloading in the reverse direction shear tests and the balanced biaxial tension test gives insight of the mechanical behavior up to very high equivalent plastic strains. Yoshida–Uemori hardening model associated with Bron–Besson orthotropic yield criterion is used to represent the in-plane mechanical behavior of the two steels. The identification procedure is based on minimization of a cost function defined over the whole database. The presented results show a very good agreement between model predictions and experiments: flow stress during loading and reverse loading as well as plastic anisotropy coefficients are well reproduced; it is shown that the work-hardening stagnation after strain path reversal is well estimated in length but Yoshida–Uemori model underestimates the rate of work-hardening.

<i>In Situ</i> Stress Measurement Method Based on X-Ray Diffraction under Biaxial Tensile Loading

The purpose of this investigation is to detect damage from stress distribution in the surface of near pre-crack tip by using X-ray diffraction technique during biaxial tension test. An measurements apparatus to measure stress distribution along pre-crack direction was fabrication by use of a biaxial tensile test device and a stress analyzer based on single exposure technique with one position sensitive proportional counter. Stress distribution with different tensile applied stress ratios were measured during biaxial tension test. As results, the shape of actual stress was keeping increase with increasing tensile applied stress. At maximum applied stress, the residual stress increases with the increasing distance from the crack tip; after reaching a maximum it gradually diminish.

Elasto–plasticity Behavior of IF Steel Sheet with Planar Anisotropy and Its Macro–Meso Modeling

Elasto–plasticity behavior of a IF steel sheet was investigated by performing uniaxial tension tests in three directions (0°, 45° and 90‚ to the rolling direction of the sheet), in-plane cyclic tension–compression test and bi-axial tension test. The sheet has strong planar r-value anisotropy (r0=2.15, r45=2.12 and r90=2.89) but very weak flow stress directionality. Equi-biaxial flow stress is as large as 1.23 times of the uniaxial flow stress. These elasto–plasticity deformation characteristics, as well as the Bauschinger effect and cyclic hardening behavior, are well described by a macro–plasticity model (Yoshida–Uemori model incorpolating with the 4th-order anisotropic yield function). Further, the simulation of elasto–plasticity stress–strain responses of the sheet were conducted by two types of crystal plasticity models, i.e., Taylor hypothesis based model and CPFEM, using the crystallographic orientation distribution data measured by neutron diffraction method. The models capture most of the above-mentioned deformation characteristics qualitatively, but the predicted anisotropy and the Bauschinger effect are weaker than those of the real material. The CPFEM gives more realistic results than the Taylor model.

Characterisation of a polymer using biaxial tension tests. Part I: Hyperelasticity

The present contribution deals with the experimental characterisation of silicone specimens and the adaptation of well-known standard material models of the finite hyperelasticity to the experimental data. Therefore, uniaxial tension tests as well as biaxial tension tests are performed. The focus of the work lies on the detailed description of a new experimental set-up and the adaptation of the material model. For this purpose, the performance of models fitted to experimental data of uniaxial tests is compared to the adjustment of the models to data from biaxial tests. The experimentalist as well as the modeller are sensitised that the adaptation of material models to experimental data won from the uniaxial tension experiments generally does not allow adequate statements with respect to the real material behaviour under multiaxial loading. The work closes with a summary and an outlook on forthcoming investigations.

Polymeric endoaortic paving: Mechanical, thermoforming, and degradation properties of polycaprolactone/polyurethane blends for cardiovascular applications

Polymeric endoaortic paving (PEAP) is a process by which a polymer is endovascularly delivered and thermoformed to coat or “pave” the lumen of the aorta. This method may offer an improvement to conventional endoaortic therapy in allowing conformal graft application with reduced risk of endoleak and customization to complex patient geometries. Polycaprolactone (PCL)/polyurethane (PU) blends of various blend ratios were assessed as a potential material for PEAP by characterizing their mechanical, thermoforming and degradation properties. Biaxial tension testing revealed that the blends’ stiffness is similar to that of aortic tissue, is higher for blends with more PCL content, and may be affected by thermoforming and degradation. Tubes of blends were able to maintain a higher diameter increase after thermoforming at higher PCL content and higher heating temperatures; 50/50 blend tubes heated to 55 °C were able to maintain 90% of the diameter increase applied. Delamination forces of the blends ranged from 41 to 235 N m −2. In a Pseudomonas lipase solution, the 50/50 blend had a 94% lower degradation rate than pure PCL, and the 10/90 blend exhibited no degradation. These results indicate that PEAP, consisting of a PCL/PU blend, may be useful in developing the next generation of endoaortic therapy.

Remarks on multiaxial fatigue limit criteria based on prismatic hulls and ellipsoids

This paper focuses on a class of multiaxial fatigue limit criteria where the equivalent shear stress amplitude is calculated by means of a scalar measure associated with a hypersurface enclosing the deviatoric stress history at a material point. We consider two hypersurfaces proposed by the authors, namely the maximum prismatic hull and the minimum Frobenius norm ellipsoid. Previous results obtained with elliptic and non-elliptic stress paths strongly suggested that such measures might always be the same. In this work we consider two counter-examples which show that these approaches are distinct. Fatigue limit criteria based on the linear combination of these measures with the maximum hydrostatic stress were applied to experimental data including: axial–torsional, biaxial tension and plane stress tests performed under harmonic and non-harmonic, synchronous and asynchronous waveforms. The predictions for both criteria fell within a 15 % scatter band.

A first-principles study on the elastic properties of single-walled carbon nanotubesg

A first-principles study is carried out to investigate the effects of structure and size on the elastic properties of single-walled carbon nanotubes (SWNTs). Ten zigzag-type and seven armchair-type SWNTs with diameters between 0.551 and 1.358nm are systematically studied. The linear elastic behaviour of the SWNTs when subjected to small deformations is studied by four virtual mechanical experiments: uniaxial strain, uniaxial stress, in-plane pure shear, and in-plane biaxial tension tests. Assuming that a SWNT should be transversely isotropic, a strain energy approach is used to calculate the Young's moduli in axial and transverse directions, major Posson's ratio, plain strain bulk, and in-plane shear moduli of the carbon nanotubes. It is found that the elastic constants are insensitive to the tube size, but show a slight dependence on the helicity. The differences in all the elastic moduli between zigzag and armchair nanotubes are within 10 per cent.

Large strain elasto-plastic model of paper and corrugated board

An anisotropic elasto-plastic constitutive model of paper material is presented. It is formulated in a spatial setting in which anisotropic properties are accounted for by use of structural variables. A multiplicative split of the deformation gradient is employed to introduce plasticity. A similar approach is used to model the plastic deformation of the substructure. The yield surface adopted is based on the Tsai–Wu failure criterion, used previously to model failure of paper material. A non-associated plasticity theory is employed to calibrate the model to experimental data. It turns out that a multi-axial loading situation is needed to calibrate the model and here a biaxial tension test is audited. The model was implemented into a finite element environment and the creasing process of a corrugated board panel is investigated.

A Study on the Evaluation of Characteristics and Useful Life Prediction of Rubber Component for Elevator Cabin

Rubber material properties and useful life evaluation are very important in design procedure to assure the safety and reliability of the rubber components. In this paper, the evaluation of characteristics and useful life prediction of rubber component for elevator cabin were experimentally investigated. The material test and accelerated heat-aging test were carried. Rubber material constants were obtained by curve fittings of simple tension, pure shear and bi-axial tension test data. Heat aging test results changes as the threshold are used for assessment of the useful life and time to threshold value were plotted against reciprocal of absolute temperature to give the Arrhenius plot. By using the rubber material and component test several useful life prediction equations for rubber component were proposed. Predicted useful life of rubber component for elevator cabin agreed fairly with the experimental lives.

Detection of the Real Plastification in a Biaxial Tension Test

Detection of the Real Plastification in a Biaxial Tension Test

A New Biaxial Tension Test Fixture for Uniaxial Testing Machine—A Validation for Hyperelastic Behavior of Rubber-like Materials

Abstract A new mechanism for a biaxial tension test is developed for loading an in-plane specimen simultaneously in two principal directions. This mechanism can be adapted to any uniaxial tension test machine and thereby it reduces the cost of conducting tests on expensive machines. It provides a uniform state of equibiaxial tension necessary for procedure characterizing the biaxial loading of any material system and particularly for understanding the hyperelastic behavior law of rubber-like materials for large deformations. The mechanism can also be utilized for evaluating an interaction coefficient of anisotropic or orthotropic materials like reinforced composites that can help in characterizing and predicting failure behavior. As a sample case, the experimental results obtained by this new mechanism are validated with the existing models for two rubber-like materials undergoing hyperelasticity.

Identification of a strain induced crystallisation model for PET under uni- and bi-axial loading: Influence of temperature dispersion

Accurate modelling of PET multiaxial behaviour is fundamental for blow moulding process optimisation. In this paper, we present the identification of a strain induced crystallisation model on uniaxial and biaxial tension tests, undertaken on PET amorphous samples above T g at various draw rates and tension speeds [Marco, Y., 2003. Caractérisation multi-axiale du comportement et de la microstructure d’un semi-cristallin: application au cas du PET. Thèse de doctorat de l’ENS de Cachan]. Using an accurate equivalent deformation, a non-Newtonian viscous model coupled with induced crystallisation seems to give a good representation of strain hardening for different kinds of solicitations. Moreover, a WLF-like parameter is identified and allows to be a representative of the range of the process temperatures with a single test at 90 °C. As temperature is a crucial parameter for both process and mechanical tests, we focus on the study of the influence of the temperature regulation on the dispersion of mechanical results. We use here a probabilistic approach giving convincing results and leading to a direct industrial application: knowing the heating regulation default of the process, one can predict the variation of the mechanical behaviour of the perform during blow moulding and therefore the variability of final product properties like thickness or crystallinity ratio.

Advances in experiments on metal sheets and tubes in support of constitutive modeling and forming simulations

This work is a review of experimental methods for observing and modeling the anisotropic plastic behavior of metal sheets and tubes under a variety of loading paths, such as biaxial compression tests; biaxial tension tests on metal sheets and tubes using closed-loop electrohydraulic testing machines; the abrupt strain path change method for detecting a yield vertex and subsequent yield loci without unloading; in-plane stress reversal tests on metal sheets; and multistage tension tests. Observed material responses are compared with the predictions of phenomenological plasticity models. Special attention is paid to the plastic deformation behavior of materials commonly used in industry, and to verifying the validity of conventional anisotropic yield criteria for those materials and associated flow rules at large plastic strains. The effects of using appropriate anisotropic yield criteria on the accuracy of simulations of forming defects, such as large springback and fracture, are also presented to highlight the importance of accurate material testing and modeling.

Development of a biaxial tensile test fixture for reinforced thermoplastic composites

A new mechanism for biaxial tension tests was developed for loading an in-plane reinforced composite laminate or any injection-molded polymeric specimen simultaneously in two principal directions. This mechanism can be adapted to any uniaxial tension test machine and, thereby, it can reduce the cost of conducting tests on expensive dedicated machines. The fixture provides a uniform state of equibiaxial tension, necessary for characterizing the biaxial state of loading on any polymeric material system and it can also be reconfigured to test non-equibiaxial tension over a short range. The mechanism is presently utilized for understanding the failure behavior of injection molded short fiber polyamide and nanoparticle-reinforced PP thermoplastic composites.

Simulation of Free Blowing of Polyethylene Terephthalate using a Thermodynamic Induced Crystallisation Model. Free Blowing Simulation

Microstructure evolution in Poly(Ethylene Terephthalate) during a blowing process has an important influence on final mechanical property (Chevalier,1999). In order to simulate blow-moulding process it is necessary to take into account this evolution. In a first part we present a thermodynamic model in the case of a simple dependence of the viscosity under the crystallisation ratio (Poitou, 2001). The model is identified on uniaxial and biaxial tension tests results. In a second part, the axisymmetric problem of membrane inflation is solved using a classical finite element technique. The simulated results are compared with experimental results on free blown preforms and the comparison is quite accurate considering the elementary form of the induced crystallisation model.

Analysis of forming limit diagram for superplastic materials

Superplastic materials show very large tensile elongation (in excess of 5000%) even if they are lowly stressed. Superplastic forming is carried out at high temperatures and relatively low strain rates. In order to control the industrial forming processes, the difficulty in predicting the failure strain of superplastic materials is main problem faced by technologists. In this paper, limit strain for superplastic materials were investigated under biaxial tension using the finite element method (FEM). To validate the results biaxial tension tests have been conducted using a fine-grained Pb-Sn alloy that shows superplastic properties at room temperature. The superplastic sheet was deformed using an experimental apparatus with dies of aspect ratios of 1:1, 15:11, 5:3 and 5:2.

A Study of the Static and Dynamic Characteristics for Automotive Rubber Mount by FEA and Experiment

An automotive transmission rubber mount is a device used in automotive systems to cushion the loads transmitted from the vehicle body structure. TM (transmission) rubber mount has been used to support engine in the vertical direction. In this study, the rubber specimens of the transmission mount are tested to obtain the hyperelastic and viscoelastic properties by the static and dynamic test, respectively. Uni-axial tension test, biaxial tension test, and pure shear test are carried out and Mooney-Rivlin constants are obtained from those static tests. Also, the viscoelastic properties such as storage and loss modulus are obtained from dynamic test. Using the static and dynamic test data, the dynamic stiffness of TM rubber mount subjected to static and dynamic load are predicted with finite element analysis. Solutions allow for comparison between FEA and experimental results. It is shown that the predictions of FEA are close to the experimental results.

Reiterated tension testing of silicone elastomer

A peristaltically actuated device, PADeMIS, composed of silicone rubber (SR) is under development for use in minimally invasive surgery. During locomotion, the device will be subject to a few thousand load changes involving varying, sometimes high, strains. The design is being optimised by finite element analysis, for which a constitutive law for the mechanical behaviour of silicone rubber is required. Uniaxial and biaxial tension tests have been performed on specimens of used silicon rubber. Synchronous fitting of uniaxial and biaxial tensile data gives significantly better results than using uniaxial or biaxial results alone to derive constitutive laws. The mechanical properties of SR were found to change from loading to loading up to few thousand cycles. Hence, simulating the deformation of SR structures is problematic. Furthermore, variability was observed between batches of SR.

Mechanical characterization of hyperelastic materials with fringe projection and optimization techniques

This paper presents a new hybrid technique for mechanical characterization of hyperelastic materials. The research is motivated by the fact that standard identification procedures based on the fitting of strain–stress curves determined experimentally from planar biaxial tests may be inaccurate for non-uniform states of deformation. Therefore, we propose an alternative approach where the difference Ω between the displacement field measured with Projection Moiré and its counterpart predicted by FEM is minimized using non-linear optimization algorithms that finally find unknown material properties. In order to check the feasibility of the new procedure, we considered a thin latex membrane modelling it as a two-parameter Mooney–Rivlin (MR) hyperelastic material. The Ω function is minimized either using optimization routines available in a commercial finite element package and by implementing a global optimizer able to deal with non-linearity and non-convexity included in the identification process. In order to check accuracy of optimization results, target values of MR constants for the latex specimen tested have previously been determined by fitting experimental stress–strain data gathered from a standard planar biaxial tension test. Results indicate that the present hybrid identification procedure can determine accurately properties of the hyperelastic material under investigation. In fact, the average residual error on displacements was less than 1% while the difference between the MR constants found with optimization and their target values was less than 3.5%.