共查询到20条相似文献,搜索用时 31 毫秒
1.
Jian Cao Wonoh Lee Hang Shawn Cheng Mark Seniw Hui-Ping Wang Kwansoo Chung 《International Journal of Plasticity》2009
To prevent a sheet specimen from buckling subjected to a tension-compression cyclic loading, a new fixture has been developed to use with a regular tensile-compression machine. The novelty of this device lies in 4-block wedge design with pre-loaded springs. This design allows blocks to freely move in the vertical direction while providing the normal support to the entire length of the specimen during the tension-compression cycle. The entire test is easy to setup, which is another advantage of this design. In order to measure the strain accurately, the transmission type laser extensometer was utilized together with the implementation of double-side fins in the specimen. Experimental results of tension-compression tests are presented followed by a review of existing testing methods. In order to describe the accurate cyclic tension-compression behavior, the combined isotropic-kinematic hardening law based on the modified Chaboche model and the practical two-surface model based on Dafalias-Popov and Krieg models have been modified in this work, considering the permanent softening behavior during reverse loading and the non-symmetric behavior during reloading. Through tension-compression tests, the material characterization has been performed for three base materials, BH180, DP600 steels and AA6111-T4 sheets. 相似文献
2.
R.K. Boger R.H. Wagoner F. Barlat M.G. Lee K. Chung 《International Journal of Plasticity》2005,21(12):2319-2343
Modeling sheet metal forming operations requires understanding of the plastic behavior of sheet alloys along non-proportional strain paths. Measurement of hardening under reversed uniaxial loading is of particular interest because of its simplicity of interpretation and its application to material elements drawn over a die radius. However, the compressive strain range attainable with conventional tests of this type is severely limited by buckling. A new method has been developed and optimized employing a simple device, a special specimen geometry, and corrections for friction and off-axis loading. Continuous strain reversal tests have been carried out to compressive strains greater than 0.20 following the guidelines provided for optimizing the test. The breadth of application of the technique has been demonstrated by preliminary tests to reveal the nature of the Bauschinger effect, room-temperature creep, and anelasticity after strain reversals in commercial sheet alloys. 相似文献
3.
基于液压伺服高速加载系统,发展了一种材料双轴拉伸力学性能测试技术。利用锥面接触导向驱动方法,把加载锤竖直方向的驱动力转化为水平方向的双轴驱动力,从而实现对十字形试样平面双轴加载。借助有限元数值模拟手段优化了锥面接触角和十字形试样尺寸。当接触锥角为45°时,既有较好的水平驱动转化效率,同时又保持较小的接触力,确保水平驱动加载各组件在弹性变形范围内,可多次重复使用。确定了加载臂狭缝个数、狭缝与减薄区边缘长度和标距段厚度等试样设计关键参数,在十字形试样测试标距段内实现了均匀变形。设计了测力夹持一体化导杆和非接触光学全场应变测试系统,准确获得了试样的应力和应变。利用此平面双轴拉伸加载装置,开展2024-T351铝合金板单轴拉伸实验和激光探测同步性验证实验,验证装置设计的可行性;开展铝合金板材在不同加载速率下的双轴拉伸实验,得到在双轴加载下铝合金板材应力应变曲线,并与单轴加载下实验结果进行了对比分析。 相似文献
4.
《International Journal of Plasticity》2002,18(5-6):743-767
The plastic response of materials during reverse loading has practical consequences for common sheet forming operations in terms of loads, localization behavior, and springback. However, it is difficult to measure the reverse loading (Bauschinger effect) in sheet materials because of their propensity to buckle. A simple reverse-bend test was constructed and used to investigate the cyclic loading of three automotive body alloys. The results showed that consideration of the Bauschinger effect is essential to obtaining agreement with such results. An inverse procedure was used to determine anisotropic hardening law parameters. Laws obtained in this way were compared with ones generated by more sensitive tension-compression tests appearing in the literature for the same alloys. The two laws were significantly different, but both produced accurate simulations of reverse-bend test load–displacement curves. Several artificial material models were then constructed to simulate the reverse-bend test and thus to probe its sensitivity to material constitutive equation details. For materials whose reverse-loading response varies with the level of prestrain, as is the case for each of the three alloys tested, a wide range of constitutive response is capable of producing identical reverse-bending behavior. The results show that inverse procedures applied to the reverse-bend test do not provide unique results, and thus the usefulness of the reverse-bend test for such investigations is limited. 相似文献
5.
《International Journal of Plasticity》2002,18(8):1111-1131
In Part 2 of this study, extensive deformation tests were carried out on the nickel-base polycrystalline superalloy IN738LC under isothermal and anisothermal conditions between 450 and 950 °C. Under the isothermal conditions, the material showed almost no rate/time-dependency below 700 °C, while it showed distinct rate/time-dependency above 800 °C. Regarding the cyclic deformation, slight cyclic hardening behavior was observed when the temperature was below 700 °C and the imposed strain rate was fast, whereas in the case of the temperature above 800 °C or under slower strain rate conditions, the cyclic hardening behavior was scarcely observed. Unique inelastic behavior was observed under in-phase and out-of-phase anisothermal conditions: with an increase in the number of cycles, the stress at higher temperatures became smaller and the stress at lower temperatures became larger in absolute value although the stress range was approximately constant during the cyclic loading. In other words, the mean stress continues to evolve cycle-by-cycle in the direction of the stress at lower temperatures. Based on the experimental results, it was assumed that evolution of the variable Y that had been incorporated into a kinematic hardening rule in Part 1 of this study is active under higher temperatures and is negligible under lower temperatures. The material constants used in the constitutive equations were determined with the isothermal data, and were expressed as functions of temperature empirically. The extended viscoplastic constitutive equations were applied to the anisothermal cyclic loading as well as the monotonic tension, stress relaxation, creep and cyclic loading under the isothermal conditions. It was demonstrated that the present viscoplastic constitutive model was successful in describing the inelastic behavior of the material adequately, including the anomalous inelastic behavior observed under the anisothermal conditions, owing to the consideration of the variable Y. 相似文献
6.
《International Journal of Plasticity》2005,21(1):43-65
Uniaxial and multiaxial ratchetting tests were conducted at temperatures between 200 and 600 °C on modified 9Cr–1Mo steel, which exhibits both viscoplastic and cyclic softening behavior. Anomalous behavior was observed in the stress-controlled uniaxial ratchetting tests; the material exhibited outstanding ratchetting in the tensile direction under zero mean stress. Under the uniaxial conditions, the ratchetting deformation significantly depended on the loading rate and hold time in addition to parameters such as the maximum stress and stress ratio. The uniaxial ratchetting was also accelerated to a great extent when cyclic deformation was given before the ratchetting tests. Under the multiaxial conditions, the ratchetting depended on the steady stress, cyclic strain range and strain rate. The ratchetting progressed faster as the steady stress or strain range became larger, or the strain rate became smaller, as expected. Monotonic compression tests were carried out to investigate the reason for the rachetting under no mean stress. Strain range change tests were also conducted to investigate the effect of strain range on the cyclic softening behavior of the material in detail. 相似文献
7.
8.
轴向交变载荷作用下螺栓联接结构的松动试验研究 总被引:1,自引:0,他引:1
在设计、试制螺栓加载装置的基础上,对螺栓联接结构进行了轴向振动的疲劳试验,获取了螺栓夹紧力的时变曲线,并对试验后的螺栓接触表面进行损伤分析,研究螺栓联接结构的松动机理.结果表明:在轴向振动条件下,螺栓联接结构的夹紧力下降较为明显,但拧出力矩相对于预紧力矩变化不大.螺栓的松动过程可分为以下两个阶段:试验初期由于螺栓接触面的塑性变形,夹紧力迅速下降;然后由于接触面之间的微动磨损,夹紧力缓慢下降.螺纹接触面之间的损伤机制主要为黏着磨损、磨粒磨损和剥层. 相似文献
9.
The multitude of in-plane shear tests existing in the literature seems to demonstrate the complexity of developing a test adapted to all experimental works. In a general framework of investigation of translaminar cracks in thin laminates, a test able to reproduce a pure in-plane shear loading was required. The laminate studied is notably employed as helicopter blade skin, and cyclic torsion induced by aerodynamic load involves cyclic in-plane shear. This particular application established some specifications for the test needed to carry out this study. To comply with them, an original technological solution has been developed from a three-rail shear test apparatus. This paper describes the resulting “reversible rail shear test” solution and its application to the study of in-plane shear behavior of a thin glass-epoxy laminate. The results concern plain and notched coupons under quasi-static loading, and crack growth tests under cyclic loading. 相似文献
10.
11.
The interferometric strain/displacement gage was used to measure local strains of approximately ± 1 percent strain near a central notch in specimens undergoing completely reversed loading. Two notch geometries were tested: a circular hole and a keyhole slot with theoretical stress-concentration factors of 3.1 and 5.9 respectively. Measurements were made at both room and elevated temperatures (149° and 260°C) on three materials having different cyclic properties. This paper describes the experimental techniques for making the notch-strain measurements. The results of this series of tests are used in evaluating Neuber's cyclic rule. 相似文献
12.
An isotropic formulation of the viscoplasticity theory for small strain and based on overstress with a differential growth law for the equilibrium stress is introduced. The four material constants and the two material functions of the theory are determined from uniaxial tensile tests involving strain-rate changes at room temperature and performed on a 6061 T6 Aluminum Alloy. Subsequently the theory is used to predict the biaxial behavior under axialtorsion loading. All tests are under strain control and involve proportional loading and axial followed by torsional straining (and vice versa). Cyclic histories include in-phase and out-of-phase cycling. The predictions of the theory are very reasonable for this cyclically neutral alloy. For cyclic hardening or softening materials a modification of the theory is necessary and is under development. 相似文献
13.
《International Journal of Plasticity》1988,4(1):77-89
The results of companion, incremental/decremental, and stepup fatigue experiments on austenitic stainless steel tube (type 304) are presented. The experiments include proportional and nonproportional loading conditions at ambient as well as elevated temperatures. Empirical relations are developed between von Mises effective stress and strain, and these relations are shown to describe the cyclic behavior during proportional companion as well as incremental/decremental tests. In case of nonproportional incremental/decremental experiments, the material behavior is not accurately modeled either by using the von Mises effective stress and strain, or by relating Tresca's maximum shear stress and strain. 相似文献
14.
A testing apparatus has been developed to study the behavior of sheet metals and composite materials under monotonic and cyclic biaxial loading conditions. This test facility employs cruciform specimens that are loaded in their plane. Problems encountered while developing the test system are discussed.We also discuss the difficulties common to test methods employing cruciform specimens. These relate to the design of a suitable specimen geometry and to the determination of the stresses throughout the specimen. A method for designing an optimal geometry for these specimens is presented. This method is based on the statistical tools of factorial and response surface designs. The statistical method, coupled with a finite-element analysis of the specimen, was successfully applied to optimize the geometry of a cruciform specimen with a circular reduced central region.Paper was presented at the 1989 SEM Spring Conference on Experimental Mechanics held in Cambridge, MA on May 28–June 8. 相似文献
15.
In order to accurately simulate the thermoforming or blowmolding manufacturing processes using finite elements or some other
suitable computational procedure, it is necessary to know the constitutive behavior of the material being formed. In this
study, an apparatus was developed to measure the large deformation behavior of thermoplastic sheet at elevated temperatures.
The specifications of the test apparatus, as well as sample data measurements are presented. Biaxial viscoelastic material
properities of ABS sheets were determined at forming temperatures. In particular, the nonlinear stress-strain relationship
of the material was experimentally measured at various temperatures above the glass transition temperature and the data correlated
to a time and strain separable viscoelastic material model. The results of this study show that it is possible to recover
the underlying nonlinear elastic response of heated ABS sheet material, at finite strains, from tests exhibiting significant
viscoelastic behavior. 相似文献
16.
《International Journal of Plasticity》1996,12(9):1123-1149
Motivated by the effect of the different loading paths (uniaxial and multiaxial) and the mean stress or strain effects, fatigue life is qualitatively evaluated by employing a micromechanical approach developed in the first part of this paper. Taking into account these loading conditions, a number of numerical tests are carried out to demonstrate the ability of this model to describe the inelastic-damaged behavior of low cyclic fatigue. Theoretically, the internal variables evolution on the Crystallographic Slip Systems (CSS) are recorded under these loadings up to the final fracture of the Representative Volume Element (RVE). The predicted macro-damage DT as well as the applied macro-stress Σ are recorded and analyzed during fatigue life. It is demonstrated that, at least qualitatively, the developed model gives successful results describing the fatigue lives under employed loading paths. Quantitatively, after the identification of the material constants of the over-aged Waspaloy, two examples are taken into consideration representing the uniaxial and biaxial cyclic behavior of this alloy. It is shown that the predicted responses are in good agreement with the experimental results. 相似文献
17.
《International Journal of Plasticity》2000,16(3-4):241-262
In this paper, a viscoplastic constitutive model previously proposed by the authors was extended to apply to the cyclic deformation analysis of the modified 9Cr-1Mo steel. A series of cyclic deformation tests were conducted on modified 9Cr-1Mo steel at various temperatures, including those under anisothermal conditions. Furthermore, cyclic evolution of state variables used in the authors' constitutive model was experimentally measured. Based on the test results, cyclic softening behavior depending on the temperature and its history was introduced into the constitutive model. The extended model was applied to simulations of inelastic deformation behavior under monotonic tension, stress relaxation, creep, isothermal cyclic deformations including stress relaxation and anisothermal cyclic deformations. It was found that the present constitutive model has a capability of describing the inelastic deformation behavior of modified 9Cr-1Mo steel adequately at various loading conditions. 相似文献
18.
Cyclic thermomechanical behavior of a polycrystalline pseudoelastic shape memory alloy 总被引:1,自引:0,他引:1
T.J. LimD.L. McDowell 《Journal of the mechanics and physics of solids》2002,50(3):651-676
In this work, 3D finite element modeling is employed to examine the thermomechanical behavior of a polycrystalline Ni-Ti shape memory alloy in the pseudoelastic regime. It is shown that the tension-compression asymmetry during uniaxial cyclic loading is due to a preferred orientation of the crystallographic texture. In pure shear loading, the thermomechanical behavior exhibits symmetry in both senses of shear, due to the fiber texture of the specimen bar stock. It is also shown that the apparent strain rate-dependence is due to thermomechanical coupling with latent heat generation/absorption during phase transformation. 相似文献
19.
When cyclic loading is applied to poroelastic materials, a transient stage of interstitial fluid pressure occurs, preceding a steady state. In each stage, the fluid pressure exhibits a characteristic mechanical behavior. In this study, an analytical solution for fluid pressure in two-dimensional poroelastic materials, which is assumed to be isotropic, under cyclic axial and bending loading is presented, based on poroelasticity. The obtained analytical solution contains transient and steady-state responses. Both of these depend on three dimensionless parameters: the dimensionless stress coefficient; the dimensionless frequency; and, the axial-bending loading ratio. We focus particularly on the transient behavior of interstitial fluid pressure with changes in the dimensionless frequency and the axial-bending loading ratio. The transient properties, such as half-value period and contribution factor, depend largely on the dimensionless frequency and have peak values when its value is about 10. This suggests that, under these conditions, the transient response can significantly affect the mechanical behavior of poroelastic materials. 相似文献
20.
Akhtar S. Khan Thomas Gnäupel-HeroldRaja K. Mishra 《International Journal of Plasticity》2011,27(5):688-706
In order to study the behavior of material under finite deformation at various strain rates, the responses of AZ31 Mg sheet are measured under uniaxial (tension and compression) and multiaxial (simple shear) loadings along rolling direction (RD), 45° to rolling direction (DD), 90° to rolling direction (TD), and normal to the sheet (ND) to large strains. The material exhibits positive strain rate sensitivity (SRS) at room and elevated temperatures; the SRS is more pronounced at high temperatures and lower strain rates. The r-value of the material under tensile loading at room temperatures is higher in TD at lower strain rate. Texture measurements on several failed specimens are reported under tension and simple shear after finite plastic deformation of about 20% equivalent strain. The as-received material exhibits a strong fiber with equal fractions of grains having the c-axis slightly tilted away from the sheet normal towards both +RD and −RD. Pole figures obtained after tensile loading along the rolling direction (RD) show that the texture of the material strengthens even at low strains, with c-axis perpendicular to the sheet plane and prism planes lining up in a majority of grains. However, the tensile loading axis along TD does not lead to similar texture strengthening; the c-axis distribution appears to be virtually unchanged from the virgin state. The pole figures obtained after in-plane compression along RD brings the c-axes of the grains parallel to the loading direction. The pole figures after simple shear loading show that the c-axis rotates to lie on the sheet plane consistent with a compression axis 45° away on the sheet plane. 相似文献