Stress-strain Material Properties Research Articles

Tensile stress strain model of polyvinyl chloride/calcium carbonate (PVC/CaCO3) nanocomposite plank

This paper presents the tensile stress strain model of a recyclable polyvinyl chloride/calcium carbonate (PVC/CaCO3) thermo-formable, fire/water proof resistant, and durable composite mineral plank. The paper presents experimentally obtained material stress-strain properties in direct tension as a function of its parameters including thickness, surface texture and grain alignment. With an increase in thickness from 1 mm (0.039 in.) to 12 mm (0.47 in.) for rough surface texture and parallel grain alignment, tensile and rupture strengths decreased from 27.4 MPa (4.11 ksi) to 14 MPa (2.1 ksi) and from 14 MPa (2.1 ksi) to 6 MPa (0.9 ksi) respectively. Strains at rupture increased from 0.01 to 0.02 while the modulus of elasticity decreased from 23078 MPa (3462 ksi) to 2139 MPa (320.85 ksi). Smoothness of surface texture increased the ultimate and rupture stresses by 16% while rupture strains increased by 45% leading to a more ductile material. Grain orientation perpendicular to the load direction resulted in an 18% reduction in ultimate strength. The paper proposes models for predicting the stress strain relationship including modulus of elasticity, toughness, stress and strain in the proportional, ultimate and rupture states in terms of the material parameters. The developed models are essential for establishing code requirements and design criteria for structural members retrofitted with this type of composite.

A Nonlinear Finite-Element Analysis Tool to Prevent Rupture of Power Transformer Tank

High-energy internal failures of transformers are catastrophic events which are hardly predictable. For this reason, a full-scale controlled experiment represents a valuable learning opportunity to gather accurate information about sequence of events during the very short time in which the failure occurs. Controlled parameters include tank design, material properties, experimental load and measurements. In this paper, we present a detailed investigation using nonlinear finite-element analysis of a 210-MVA transformer high-pressure experiment. We begin by evaluating the relationship between internal arcing pressure rise and tank expansion characteristics. Since this relationship is not linear due to geometric and material nonlinearities, an iterative process is proposed to ensure result accuracy. Stress–strain material properties are retrieved by tension experiments of specimens extracted from the tested tank to enable accurate comparison of numerical and experimental results. It is shown in this paper that nonlinear material parameters have a small influence on the tank pressure rise, but a significant one on large strain prediction and therefore the true stress-strain curve is recommended. In addition, the ductile rupture criterion based on the ultimate plastic strain of the material correlates with the experimental and explicit dynamic analysis results. This can ensure a certain design margin for tank rupture prevention.

ОБЕСПЕЧЕНИЕ КАЧЕСТВА МАШИН НА ОСНОВЕ СОВЕРШЕНСТВОВАНИЯ МЕТОДОВ И СРЕДСТВ ОЦЕНКИ ТРИБОТЕХНИЧЕСКИХ ПАРАМЕТРОВ ИХ ФУНКЦИОНАЛЬНЫХ УЗЛОВ

The choice of possible ways for machinery quality increase must be based on the investigation results of wear regularities and also on the experimental data obtained in the course of laboratory nature and production method use with the aid corresponding equipment use. 
 The purpose of the work is updating methods and means for the estimate of tribo-technical unit operation parameters. 
 Tribo-technical tests must reproduce a wide range of events taking place at different interactions of machinery surface layers with wear environment under different conditions of operation. The more trustworthy the estimated figures in the course of the experiments carried out, the larger potentialities for quality increase of products manufactured. To obtain reliable data the essential condition is the reproduction of conditions taking place in the course of the operation of the samples under investigation. The modeling of parts wear processes on the plants presented and reproducing wear mechanisms under conditions of operation allows revealing the peculiarities of a contact interaction, wear regularities and defining the efficient ways for parts life increase ensuring proper quality of products manufactured. 
 The methods and equipment developed for tribo-technical parameter estimate allow characterizing more precisely the values of physical stress-strain properties of materials under investigation and sure forecasting the working capacity of friction units under specified conditions of operation.

Experimental assessment of stiffness and energy dissipation properties of disk-shaped polymer-based composite specimens by in-plane torsion testing

Torsion testing machines are widely used either to measure the strength, stiffness and stress-strain properties of materials or to replicate real-life service conditions. In this paper, a novel experimental method is presented, based on the development of a dedicated steel structure to be used in conjunction with a universal testing machine. This equipment allows applying cyclic in-plane torsion loads on disk-shaped components. The proposed approach aims to enable the assessment of stiffness and damping properties on specimens enabling the application of higher loads in comparison with the traditional machines.Specifically, dynamic trials were performed by attaching the composite specimens and the steel structure to the testing machine, such that the uniaxial controlled displacements can be used to exert the desired cyclic loads onto the specimen. Both torsional stiffness and energy loss were measured from the steady-state load-displacement hysteresis cycles. Amplitudes of sine signals, from 0.05 to 0.2 mm, and a frequency ranging between 1 and 20 Hz, were used in the experiments. The results are presented comparing the behaviour of two polymer matrix composites, with the same number of identical laminae, but characterized by different stacking sequences, namely unidirectional and quasi-isotropic configurations.

Влияние процесса упрочнения волной деформации на микроструктуру материала

The paper reports the investigation results of combined strengthening impact upon material micro-structure changes. On the basis of the investigations carried out there is described an impact of wave deformation strengthening process upon material micro-structure by the example of chromium-nickel alloyed steels. It is shown that ChTT+SPD strengthening ensures the increase of material stress-strain properties.

The effect of material stress-strain characteristics on the ultimate stress and critical buckling strain of flat plates subjected to uniform axial compression

The buckling capacity of uniformly compressed flat plates has been investigated in this study. Material properties were characterized based on parameterization of the stress-strain curves using a simple and novel mathematical expression. Idealized stress-strain relationships were developed using the proposed material model and extensive parametric numerical analyses were conducted to investigate the effect of the material stress-strain properties on the buckling capacity of flat plates. For stress-strain curves with a yield plateau, the results of the parametric study showed a minimal influence of the material properties on the buckling capacity of the plates whereas a significant effect of the strain-hardening properties was observed in plates with round-house curves. Ultimately, the proposed stress-strain model was shown to be remarkably useful for capturing the relevant intricacies associated with material nonlinearity when predicting the buckling capacity and post-buckling behavior of uniformly-compressed flat plates.

Finite-element calculations of thin-walled structures of concatenated shells with different material stress–strain properties

The algorithm for calculating the stressed-deformed state (SDS) of thin-walled structures of concatenated shells with different material stress–strain properties on the finite-element method’s base with scalar and vector interpolation of displacement fields has been outlined. The quadrangular curvilinear finite-element with nine degrees of freedom in the node has been used as a discretization element. The SDS analysis of a thin-walled shell structure formed by a cylinder and two jointed shells of dissimilar materials has been performed.

МОДИФИКАЦИЯ МАТЕРИАЛОВ В ТЛЕЮЩЕМ РАЗРЯДЕ

The development of new methods to improve physical and stressstrain properties of materials is an important contribution to the development of modern technologies and targeted control of their behavior. The optimum combination of stressstrain properties and electrical ones to improve performance attributes of materials is very important. The basic purpose of this work is the study of long-term effects in materials resistivity changes after treatment in a glow discharge. There are presented the results of measurements of a resistivity relative value in copper-graphite insertions after a radiation treatment in a glow discharge. The graphic dependences obtained show that in the course of two years in samples a long-lived state, a structure of irradiated composite material remains. It is a sign of that the improvement of performance attributes of insertions investigated bears longterm character. An anomalous temperature dependence of electric resistance after an irradiation treatment if a glow discharge was detected in technical copper samples. First of all this anomaly manifests itself in copper resis-tivity decrease after an irradiation treatment at different temperatures obtained that is contrary to the fact determined of the simultaneous increase of dislocations density in samples irradiated.

Effects of different restraints on the weld-induced residual deformations and stresses in a steel plate

Effects of three different plate boundary constraints on the residual stress field and deformation are investigated numerically during butt-joint welding. For the numerical solution of the heat transfer equations, the finite element method is used to predict the temperature profile as well as residual stress field due to three different plate boundary conditions. The distortion of the welded plate is modeled as a nonlinear problem in geometry and material, adopting a finite element solution based upon the thermo–elastic–plastic large deflection theory. High-strength shipbuilding steel AH36 with temperature-depending material properties and nonlinear stress–strain material properties (bilinear isotropic hardening option uses the von Mises yield criteria) are assumed for the numerical analysis. For verifying the results, the temperature profile is compared with the result obtained in a previous research. In the mechanical analysis, three different boundary conditions are applied. Effects of plate thickness, plate width, and mesh model on the residual stress with boundary constraint are studied.

Design methodologies for reliability of SSL LED boards

This work presents a comparison of various LED board technologies from thermal, mechanical and reliability point of view provided by an accurate 3-D modelling. LED boards are proposed as a possible technology replacement of FR4 LED boards used in 400 lumen retrofit SSL lamps. Presented design methodology can be used for other high power SSL lamp designs. The performance of new LED board designs were evaluated by numerical modeling. Modeling methodology was proven by measurement on reference FR4 LED board. Thermal performance was compared by extracting of LED boards thermal resistances and thermal stress has been inspected considering the widest temperature operating range according to standards (−40 to +125°C). Thermo-mechanical and reliability analysis have been performed to study parameters of each LED board technology, using thermal boundary conditions extracted from the thermal simulation of a whole LED lamp. Elastic–plastic analysis with temperature dependent stress–strain material properties has been performed. The objective of the work is to optimize not only the thermal management by thermal simulation of LED boards, but also to find potential problems from mechanical failure point of view and to present a methodology to design SSL LED boards for reliability.

A study of dynamic testing of single solder joints and its application to finite element modelling

Intermetallic compounds, impurities, voids, and other inhomogeneities are formed in solder joints of integrated-circuit packages. Consequently, the mechanical response of these interconnections may not be well modelled if the properties of bulk solder alloy alone are used. This investigation explores the feasibility of eliciting the dynamic response of single-solder-joint specimens through split-Hopkinson-bar (SHB) testing. As solder joints are extremely small, contact between such specimens and the input–output bars of an SHB results in high stress localization. Numerical simulation of SHB testing of a small specimen, the size of a solder joint, is undertaken using Abaqus to validate the assumption of one-dimensional plane wave propagation in the input–output bars, as well as the accuracy of results derived from the strain signals associated with the midpoints of the bars. Uniaxial compression and tensile tests on single-solder-joint specimens are also conducted at deformation rates ranging from 0.000 15 mm/s to 1.4 m/s. The rate sensitivity is observed and force–deformation curves are obtained, as the actual solder joints possess a barrel-like geometry. In order to apply the force–deformation responses in finite element method (FEM) modelling, a numerical study is also undertaken to investigate the possibility of idealizing the barrel-like solder joint geometry by a cylinder. Subsequently, experimentally measured force–deformation responses of single solder joints are converted into ‘normalized’ or ‘equivalent’ stress–strain material properties. Equivalent stress–strain curves for uniaxial tension at strain rates of 0.0005–1000 s×1, and uniaxial compression at strain rates of 0.0005–5000 s×1 are derived. The variation in the equivalent yield stress with the strain rate is identified and a curve fit is applied. Initial implementation of the equivalent stress–strain curves, together with an idealized cylindrical solder connection, into FEM modelling demonstrates that this is able to predict the mechanical response of solder joints in tension, compression, and shear with reasonable accuracy.

Effect of Pressure on Stress-Strain Properties of Materials

The transition from brittleness to ductility in the mechanical behavior of materials with increase in the hydrostatic component of the stress reflects differences in the pressure dependence of the stress needed to initiate particular processes of fracture or flow. The simple hypothesis that processes involving ordinary friction in the relative movement of grains or fracture fragments are highly pressure dependent, whereas crystallographic slip and twinning are not, is examined in the light of recent experimental results on phyllite, galena, and magnesium oxide. There is indication that some slip systems, perhaps ''intrinsically hard'' ones, can be fairly pressure dependent so that the above generalization may not always be valid, but more experimental evidence is needed. (23 refs.)

Predicting fracture and fatigue crack growth properties using tensile properties

The safe-life assessment of components requires information such as the plane stress ( K c ), plane strain ( K Ic ), part-through fracture toughness ( K Ie ), and the fatigue crack growth rate properties. A proposed parametric/theoretical approach, based on an extended Griffith theory is used to derive fracture toughness properties and generate fatigue crack growth rate data for a range of alloys. The simplicity of the concept is based on the use of basic, and in most cases available, uniaxial stress–strain material properties data to derive material fracture toughness values. However since the methodology is in part based on an empirical relationship a wide ranging validation with actual data is required. This paper uses steel, aluminum and titanium based alloys from a pedigree database to quantify material properties sensitivity to the predictions for K Ic and K c and the subsequent estimation of Δ K th threshold and the Paris constants, C and n values. A sensitivity analysis using experimental scatter bounds show the range of d a/d N predictions can be achieved. It is found K Ic /Δ K th ratios designated as α has a range of 5–25 irrespective of tensile ductility, ε f , and is insensitive to it. The value of Δ K th for all the alloys considered was found to be proportional to the final elongation, ε f , and an empirical relationship describing Δ K th as a function of ε f was established. Furthermore it is suggested that, with the knowledge of appropriate tensile properties and the estimated range of K Ic /Δ K th ratios for the different alloys applying this method could be an appropriate tool that can be used to conservatively predict fracture and fatigue in similar alloy categories. Thus helping to reduce costs and optimize the number of experimental tests needed for alloy characterizations.

The Identation Size Effect and Hall-Petch Behaviour of Annealed Polycrystalline Copper

AbstractMethods to obtain tensile stress-strain properties of materials from a practically non-destructive indentation test are of great industrial interest. However, to do this successfully, indentation size effects must be accounted for. Many indentation size effects, such as strain gradient plasticity and micro-pillar experiments [1], show a size dependence proportional to the inverse square root of a length scale, in common with Hall-Petch behavior. Recently, however, the indentation size effect from small radius spherical indenters has been shown, for a range of fcc metals, not to follow a Hall-Petch-like relationship but to be proportional to the inverse cube root of indenter radius [2]. Here, we investigate these differences further and present results for the indentation size effect with spherical indenters on Cu samples that have been engineered to have different grain sizes. The important experimental control parameter of the relative size of the indentation compared to the grain size is also explored since the cross over from grains significantly smaller than the contact radius to grains significantly larger than the contact radius occurs at different length scales in each sample. A thorough understanding of the various length-scale effects in the different test methods (e.g. the indentation size effect and grain size effect in indentation), is essential if a relationship, robust enough for industrial application, is to be defined to obtain tensile properties from an essentially non-destructive indentation test.

Finite element investigation of steel built-up shear links subjected to inelastic deformations

Non-linear finite element models accounting for large displacements have been used to investigate the behavior of steel built-up shear links that had previously been tested using large-scale experiments. The links were designed using steel grades with yield points ranging from high to low strengths. The objectives of the numerical analyses were to further investigate the non-linear behavior and to correlate the numerical results with experimental observations. Elasto-plastic as well as cyclic stress-strain material properties were incorporated to study the influence of material behavior on the overall shear link response. Non-linear monotonie analyses of the shear links incorporating the cyclic stress-strain steel properties resulted in similar trends in the response as the backbone curves recorded from the physical experiments. The numerical models of built-up shear links utilizing structural grade steels closely correlated to the experimentally recorded shear strength. Models utilizing low yield point steels overestimated the shear strength, which was caused by the characteristics of cyclic behavior of those steels. The detailed numerical models also allowed for investigation of the plastic strain demands on the different components of the link. It was shown that finite element models combined with appropriate stress-strain relationship may be used with confidence to check the design of shear links of different steel grades and sectional geometries.

高靱性型セメント系複合材料の一軸引張 : 圧縮繰り返し試験方法の提案

This paper proposes and describes a new test method for ductile cementitious composite materials to evaluate the basic material stress-strain properties under tension, compression, and tension-compression reversed cyclic loading conditions. Those properties are indispensable for identification of materials and for evaluating the performance of structural elements utilizing ductile cementitious composite materials. Required condition for the test method, some problems in the conventional tension tests, details of the development for the test method, and verification of the test results in comparison with those of the conventional standard test methods for tension and compression of concrete are presented.

Effects of age on elastic moduli of human lungs.

The model of the lung as an elastic continuum undergoing small distortions from a uniformly inflated state has been used to describe many lung deformation problems. Lung stress-strain material properties needed for this model are described by two elastic moduli: the bulk modulus, which describes a uniform inflation, and the shear modulus, which describes an isovolume deformation. In this study we measured the bulk modulus and shear modulus of human lungs obtained at autopsy at several fixed transpulmonary pressures (Ptp). The bulk modulus was obtained from small pressure-volume perturbations on different points of the deflation pressure-volume curve. The shear modulus was obtained from indentation tests on the lung surface. The results indicated that, at a constant Ptp, both bulk and shear moduli increased with age, and the increase was greater at higher Ptp values. The micromechanical basis for these changes remains to be elucidated.

Inelastic buckling analyses of beams, columns and plates using the spline finite strip method

A method of inelastic buckling analysis of thin-walled structural members and plates is described. The method is based on the spline finite strip method of structural analysis. The analysis takes into account the non-linear material stress-strain properties, strain hardening and residual stresses. The plastic theories used in the study are the flow theory of plasticity and the deformation theory of plasticity. The method of inelastic buckling analysis is applied to a variety of instability problems including plates, cold-formed columns, hot-rolled columns and welded tee section beams. The buckling modes and loads computed are compared with theoretical values and test results.

A Simplified Method for Elastic-Plastic-Creep Structural Analysis

A simplified inelastic analysis computer program (ANSYMP) was developed for predicting the stress-strain history at the critical location of a thermomechanically cycled structure from an elastic solution. The program uses an iterative and incremental procedure to estimate the plastic strains from the material stress-strain properties and a plasticity hardening model. Creep effects can be calculated on the basis of stress relaxation at constant strain, creep at constant stress or a combination of stress relaxation and creep accumulation. The simplified method was exercised on a number of problems involving uniaxial and multiaxial loading, isothermal and nonisothermal conditions, dwell times at various points in the cycles, different materials, and kinematic hardening. Good agreement was found between these analytical results and nonlinear finite element solutions for these problems. The simplified analysis program used less than 1 percent of the CPU time required for a nonlinear finite element analysis.