The Experts below are selected from a list of 30 Experts worldwide ranked by ideXlab platform
Yanyao Jiang - One of the best experts on this subject based on the ideXlab platform.
-
an experimental study of cyclic deformation of extruded az61a magnesium alloy
International Journal of Plasticity, 2011Co-Authors: Jixi Zhang, Yanyao JiangAbstract:Abstract Thin-walled tubular specimens were employed to study the cyclic deformation of extruded AZ61A magnesium alloy. Experiments were conducted under fully reversed strain-controlled tension–compression, torsion, and combined axial–torsion in ambient air. Mechanical twinning was found to significantly influence the inelastic deformation of the material. Cyclic Hardening was observed at all the strain amplitudes under investigation. For tension–compression at strain amplitudes higher than 0.5%, the stress–strain hysteresis loop was asymmetric with a positive mean stress. This was associated with mechanical twinning in the compression phase and detwinning in the subsequent tension phase. Under cyclic torsion, the stress–strain hysteresis loops were symmetric although mechanical twinning was observed at high shear strain amplitudes. When the material was subjected to combined axial–torsion loading, the alternative occurrence of twinning and detwinning processes under axial stress resulted in asymmetric shear stress–shear strain hysteresis loops. Nonproportional Hardening was not observed due to limited number of slip systems and the formation of mechanical twins. Microstructures after the stabilization of cyclic deformation were observed and the dominant mechanisms governing cyclic deformation were discussed. Existing cyclic plasticity models were discussed in light of their capabilities for modeling the observed cyclic deformation of the magnesium alloy.
-
constitutive modeling of cyclic plasticity deformation of a pure polycrystalline copper
International Journal of Plasticity, 2008Co-Authors: Jixi Zhang, Yanyao JiangAbstract:Abstract Cyclic plasticity experiments were conducted on a pure polycrystalline copper and the material was found to display significant cyclic Hardening and Nonproportional Hardening. An effort was made to describe the cyclic plasticity behavior of the material. The model is based on the framework using a yield surface together with the Armstrong–Frederick type kinematic Hardening rule. No isotropic Hardening is considered and the yield stress is assumed to be a constant. The backstress is decomposed into additive parts with each part following the Armstrong–Frederick type Hardening rule. A memory surface in the plastic strain space is used to account for the strain range effect. The Tanaka fourth order tensor is used to characterize Nonproportional loading. A set of material parameters in the Hardening rules are related to the strain memory surface size and they are used to capture the strain range effect and the dependence of cyclic Hardening and Nonproportional Hardening on the loading magnitude. The constitutive model can describe well the transient behavior during cyclic Hardening and Nonproportional Hardening of the polycrystalline copper. Modeling of long-term ratcheting deformation is a difficult task and further investigations are required.
-
benchmark experiments and characteristic cyclic plasticity deformation
International Journal of Plasticity, 2008Co-Authors: Yanyao Jiang, Jixi ZhangAbstract:Key issues in cyclic plasticity modeling are discussed based upon representative experimental observations on several commonly used engineering materials. Cyclic plasticity is characterized by the Bauschinger effect, cyclic Hardening/softening, strain range effect, nonproporitonal Hardening, and strain ratcheting. Additional Hardening is identified to associate with ratcheting rate decay. Proper modeling requires a clear distinction among different types of cyclic plasticity behavior. Cyclic Hardening/softening sustains dependent on the loading amplitude and loading history. Strain range effect is common for most engineering metallic materials. Often, Nonproportional Hardening is accompanied by cyclic Hardening, as being observed on stainless steels and pure copper. A clarification of the two types of material behavior can be made through benchmark experiments and modeling technique. Ratcheting rate decay is a common observation on a number of materials and it often follows a power law relationship with the number of loading cycles under the constant amplitude stress controlled condition. Benchmark experiments can be used to explore the different cyclic plasticity properties of the materials. Discussions about proper modeling are based on the typical cyclic plasticity phenomena obtained from testing several engineering materials under various uniaxial and multiaxial cyclic loading conditions. Sufficient experimental evidence points to the unambiguous conclusion that none of the Hardening phenomena (cyclic Hardening/softening, strain range effect, Nonproportional Hardening, and strain Hardening associated with ratcheting rate decay) is isotropic in nature. None of the Hardening behavior can be properly modeled with a change in the yield stress.
Jixi Zhang - One of the best experts on this subject based on the ideXlab platform.
-
an experimental study of cyclic deformation of extruded az61a magnesium alloy
International Journal of Plasticity, 2011Co-Authors: Jixi Zhang, Yanyao JiangAbstract:Abstract Thin-walled tubular specimens were employed to study the cyclic deformation of extruded AZ61A magnesium alloy. Experiments were conducted under fully reversed strain-controlled tension–compression, torsion, and combined axial–torsion in ambient air. Mechanical twinning was found to significantly influence the inelastic deformation of the material. Cyclic Hardening was observed at all the strain amplitudes under investigation. For tension–compression at strain amplitudes higher than 0.5%, the stress–strain hysteresis loop was asymmetric with a positive mean stress. This was associated with mechanical twinning in the compression phase and detwinning in the subsequent tension phase. Under cyclic torsion, the stress–strain hysteresis loops were symmetric although mechanical twinning was observed at high shear strain amplitudes. When the material was subjected to combined axial–torsion loading, the alternative occurrence of twinning and detwinning processes under axial stress resulted in asymmetric shear stress–shear strain hysteresis loops. Nonproportional Hardening was not observed due to limited number of slip systems and the formation of mechanical twins. Microstructures after the stabilization of cyclic deformation were observed and the dominant mechanisms governing cyclic deformation were discussed. Existing cyclic plasticity models were discussed in light of their capabilities for modeling the observed cyclic deformation of the magnesium alloy.
-
constitutive modeling of cyclic plasticity deformation of a pure polycrystalline copper
International Journal of Plasticity, 2008Co-Authors: Jixi Zhang, Yanyao JiangAbstract:Abstract Cyclic plasticity experiments were conducted on a pure polycrystalline copper and the material was found to display significant cyclic Hardening and Nonproportional Hardening. An effort was made to describe the cyclic plasticity behavior of the material. The model is based on the framework using a yield surface together with the Armstrong–Frederick type kinematic Hardening rule. No isotropic Hardening is considered and the yield stress is assumed to be a constant. The backstress is decomposed into additive parts with each part following the Armstrong–Frederick type Hardening rule. A memory surface in the plastic strain space is used to account for the strain range effect. The Tanaka fourth order tensor is used to characterize Nonproportional loading. A set of material parameters in the Hardening rules are related to the strain memory surface size and they are used to capture the strain range effect and the dependence of cyclic Hardening and Nonproportional Hardening on the loading magnitude. The constitutive model can describe well the transient behavior during cyclic Hardening and Nonproportional Hardening of the polycrystalline copper. Modeling of long-term ratcheting deformation is a difficult task and further investigations are required.
-
benchmark experiments and characteristic cyclic plasticity deformation
International Journal of Plasticity, 2008Co-Authors: Yanyao Jiang, Jixi ZhangAbstract:Key issues in cyclic plasticity modeling are discussed based upon representative experimental observations on several commonly used engineering materials. Cyclic plasticity is characterized by the Bauschinger effect, cyclic Hardening/softening, strain range effect, nonproporitonal Hardening, and strain ratcheting. Additional Hardening is identified to associate with ratcheting rate decay. Proper modeling requires a clear distinction among different types of cyclic plasticity behavior. Cyclic Hardening/softening sustains dependent on the loading amplitude and loading history. Strain range effect is common for most engineering metallic materials. Often, Nonproportional Hardening is accompanied by cyclic Hardening, as being observed on stainless steels and pure copper. A clarification of the two types of material behavior can be made through benchmark experiments and modeling technique. Ratcheting rate decay is a common observation on a number of materials and it often follows a power law relationship with the number of loading cycles under the constant amplitude stress controlled condition. Benchmark experiments can be used to explore the different cyclic plasticity properties of the materials. Discussions about proper modeling are based on the typical cyclic plasticity phenomena obtained from testing several engineering materials under various uniaxial and multiaxial cyclic loading conditions. Sufficient experimental evidence points to the unambiguous conclusion that none of the Hardening phenomena (cyclic Hardening/softening, strain range effect, Nonproportional Hardening, and strain Hardening associated with ratcheting rate decay) is isotropic in nature. None of the Hardening behavior can be properly modeled with a change in the yield stress.
D F Socie - One of the best experts on this subject based on the ideXlab platform.
-
dislocation structure and non proportional Hardening of type 304 stainless steel
Fatigue & Fracture of Engineering Materials & Structures, 1997Co-Authors: S Kida, Takamoto Itoh, Masao Sakane, Masateru Ohnami, D F SocieAbstract:ABSTRACT This paper describes the microstructure of Type 304 stainless steel after cyclic loading at room temperature under tension-torsion Nonproportional strain paths. The degree of cyclic Nonproportional Hardening is correlated with changes in the dislocation substructure. Dislocation cells, dislocation bundles, twins and stacking faults are all observed. The type of microstructure formed and resultant stress response is dependent on the degree of Nonproportional loading and strain range. Cyclic stress range was uniquely correlated with mean cell size.
-
Constitutive Modeling of Metals Under Nonproportional Loading,"
1991Co-Authors: S H Doong, D F SocieAbstract:Introduction In the last decade, a number of plasticity models (Lamba andSidebottom, 1978a Since Nonproportional Hardening is a complex function of the loading history, modeling of these deformation features has not been very successful. So far, the degree of Nonproportional cyclic Hardening can be accurately estimated for only a limited number of loading paths. Deformation features such as the partial recovery of Nonproportional Hardening and the cross Hardening behavior of metals are either ignored or poorly modeled. Many of these models have a complex mathematical formulation and require a large number of material constants, which limits their applications in routine engineering analysis. The inability of many models to effectively model the Nonproportional Hardening behavior appears to result from the lack of consideration of material anisotropy that occurs in many materials after plastic deformation. A recent study b
Michael Vormwald - One of the best experts on this subject based on the ideXlab platform.
-
deformation behaviour short crack growth and fatigue livesunder multiaxial Nonproportional loading
International Journal of Fatigue, 2006Co-Authors: J Hoffmeyer, Ralph Doring, Timm Seeger, Michael VormwaldAbstract:Abstract Experimental results of a research project on short crack growth under multiaxial Nonproportional loading are presented. Fatigue lives, crack growth curves and the deformation behaviour of hollow tube specimens and notched specimens were investigated under combined tension and torsion loading. The results served as basis for the development of a cyclic plasticity model [Doring R, Hoffmeyer J, Vormwald M, Seeger T. A plasticity model for calculating stress–strain sequences under multiaxial Nonproportional cyclic loading. In: Comput Mater Sci. 28(3–4);2003:587–96; Doring R, Hoffmeyer J, Seeger T, Vormwald M. Constitutive modelling of Nonproportional Hardening, cyclic Hardening and ratchetting. In: Proceedings of the seventh international conference on biaxial/multiaxial fatigue and fracture, DVM, Berlin; 2004. p. 291–6; Hoffmeyer J. Anrisslebensdauervorhersage bei mehrachsiger Beanspruchung auf Basis des Kurzrisskonzepts. PhD-Thesis, TU Darmstadt; 2004.] and a short crack model [Hoffmeyer J. Anrisslebensdauervorhersage bei mehrachsiger Beanspruchung auf Basis des Kurzrisskonzepts. PhD-Thesis, TU Darmstadt; 2004; Doring R, Hoffmeyer J, Seeger T, Vormwald M. Fatigue lifetime prediction based on a short crack growth model for multiaxial Nonproportional loading. In: Proceedings of the seventh international conference on biaxial and multiaxial fatigue and fracture, DVM, Berlin; 2004. p. 253–8]. Stress–strain paths including Nonproportional Hardening and experimental fatigue lives of the unnotched specimens under different loading cases are discussed and compared with calculations. Load-time-sequences were in-phase, 45° and 90° out-of-phase loading with constant and variable amplitudes, torsion without and with superimposed static normal stress, and strain paths like box, butterfly, diamond and cross path. For the notched specimens fatigue lives under 0° and 90° out-of-phase loading are compared with calculations based on finite element results and the short crack model. During some tests the initiation, growth and orientation of short cracks was studied using the plastic replica technique.
Zhongping Zhang - One of the best experts on this subject based on the ideXlab platform.
-
an improved armstrong frederick type plasticity model for stable cyclic stress strain responses considering Nonproportional Hardening
Journal of Materials Engineering and Performance, 2018Co-Authors: Zhongping ZhangAbstract:This paper modified an Armstrong–Frederick-type plasticity model for investigating the stable cyclic deformation behavior of metallic materials with different sensitivity to Nonproportional loadings. In the modified model, the Nonproportionality factor and Nonproportional cyclic Hardening coefficient coupled with the Jiang–Sehitoglu incremental plasticity model were used to estimate the stable stress–strain responses of the two materials (1045HR steel and 304 stainless steel) under various tension–torsion strain paths. A new equation was proposed to calculate the Nonproportionality factor on the basis of the minimum normal strain range. Procedures to determine the minimum normal strain range were presented for general multiaxial loadings. Then, the modified model requires only the cyclic strain Hardening exponent and cyclic strength coefficient to determine the material constants. It is convenient for predicting the stable stress–strain responses of materials in engineering application. Comparisons showed that the modified model can reflect the effect of Nonproportional cyclic Hardening well.
