Numerical Investigation on the Necessity of a Constant Strain Rate Condition According to Material’s Dynamic Response Behavior in the SHPB Test

2019 ◽  
Vol 59 (4) ◽  
pp. 427-437 ◽  
Author(s):  
H.R. Zou ◽  
W.L. Yin ◽  
C.C. Cai ◽  
Z. Yang ◽  
Y.B. Li ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Strain Rate ◽  
Numerical Investigation ◽  
Constant Strain Rate ◽  
Response Behavior ◽  
Rate Condition ◽  
Strain Rate Condition ◽  
Shpb Test

Cavity of Al-Cu-Mg Alloy during Superplastic Deformation

2007 ◽  
Vol 551-552 ◽  
pp. 645-650
Author(s):  
Min Wang ◽  
Hong Zhen Guo ◽  
Y.J. Liu
Keyword(s):  
Strain Rate ◽  
Grain Boundaries ◽  
Superplastic Deformation ◽  
Room Temperature ◽  
Mg Alloy ◽  
Deformation Condition ◽  
Second Phase ◽  
Rate Condition ◽  
Second Phase Particles ◽  
Strain Rate Condition

According to the characteristic of appearing cavitation in the metals during superplastic deformation, the influence of strain rate on cavity evolvement, the influence of cavity on superplastic deformation capability, and the formation, development process of cavity were investigated for Al-Cu-Mg alloy (i.e. coarse–grained LY12). The results show that: ①The pore nucleation occurs not only at triangle grain boundaries, but also along nearby the second phase particles, and even within grains. The cavities at the triangle grain boundaries are present in V-shape, others near the second phase particles and within grains are present in O-shape. These cavities may result from disharmony slippage of grain boundaries. ②The tendency of cavity development decreases with increasing of strain-rate. In lower strain-rate condition, though Al-Cu-Mg alloy has better superplasticity, many big cavities in the specimen may reduce the room temperature properties of the alloy. In higher strain-rate condition, Al-Cu-Mg alloy has certain superplasticity and room temperature properties as well as few cavities forming. By analyzing, viscous layer on grain boundaries is very thin and grain sizes can be refined during their extruding and rotating each other in higher strain-rate superplastic deformation condition. ③Growth and coalescence of cavity are the main reason of the superplastic fracture of Al-Cu-Mg alloy. And small and a certain amount of cavities with dispersion and independence state are very useful to crystal boundary slippage.

scholarly journals Critical Strain for Dynamic Recrystallisation. The Particular Case of Steels

Metals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 135 ◽  
Author(s):  
Gonzalo Varela-Castro ◽  
José-María Cabrera ◽  
José-Manuel Prado
Keyword(s):  
Critical Strain ◽  
Flow Behavior ◽  
Constitutive Models ◽  
Constant Strain Rate ◽  
Microalloyed Steels ◽  
Energy Materials ◽  
Rate Condition ◽  
Wide Range ◽  
Dynamic Recrystallisation ◽  
Strain Rate Condition

The knowledge of the flow behavior of metallic alloys subjected to hot forming operations has particular interest for metallurgists in the practice of industrial forming processes involving high temperatures (e.g., rolling, forging, and/or extrusion operations). Dynamic recrystallisation (DRX) occurs during high temperature forming over a wide range of metals and alloys, and it is known to be a powerful tool that can be used to control the microstructure and mechanical properties. Therefore, it is important to know, particularly in low stacking fault energy materials, the precise time at which DRX is available to act. Under a constant strain rate condition, and for a given temperature, such a time is defined as a critical strain (εc). Unfortunately, this critical value is not always directly measurable on the flow curve; as a result, different methods have been developed to derive it. Focused on carbon and microalloyed steels subjected to laboratory-scale testing, in the present work, the state of art on the critical strain for the initiation of DRX is reviewed and summarized. A review of the different methods and expressions for assessing the critical strain is also included. The collected data are well suited to feeding constitutive models and computational codes.

A Constitutive Model for Strain-Induced Crystallization in Poly(ethylene terephthalate) (PET) during Finite Strain Load-Hold Simulations

2005 ◽  
Vol 128 (1) ◽  
pp. 28-33 ◽  
Author(s):  
Rebecca B. Dupaix ◽  
Dwarak Krishnan
Keyword(s):  
Constitutive Model ◽  
Strain Rate ◽  
Complex Loading ◽  
Deformation Condition ◽  
Loading Conditions ◽  
Rate Condition ◽  
Strain Induced Crystallization ◽  
Strain Rate Condition ◽  
Poly Ethylene ◽  
Induced Crystallization

Recently, a hyperelastic-viscoplastic constitutive model was developed for PET and the noncrystallizing copolymer PETG (R. B. Dupaix, Ph.D. thesis, MIT, 2003). The materials were found to behave very similarly under monotonic loading conditions and the single constitutive model was able to capture both materials’ behavior. However, differences were observed upon unloading, and it is expected that additional differences would be observed under more complex loading conditions. Here their behavior is investigated under nonmonotonic loading conditions, specifically under load-hold conditions. The model of Dupaix and Boyce (R. B. Dupaix, Ph.D. thesis, MIT, 2003) is modified to include Ahzi’s upper-bound model for strain-induced crystallization [Ahzi et al., Mech. Mater., 35(12), pp. 1139–1148 (2003)]. The crystallization model is adapted to include criteria for the onset of strain-induced crystallization which depend on strain rate and level of deformation. The strain-rate condition prevents crystallization from beginning prior to the deformation process slowing significantly. The level-of-deformation condition delays crystallization until the material has deformed beyond a critical level. The combined model demonstrates differences in behavior between PET and PETG during complex loading situations, indicating its ability to capture the fundamental criteria for the onset of strain-induced crystallization.

Fatigue Behavior of A356 Cast Aluminum Alloy Microstructurally Modified by Friction Stir Processing under Low Strain Rate Condition

2012 ◽  
Vol 525-526 ◽  
pp. 169-172
Author(s):  
Toshifumi Kakiuchi ◽  
Yoshihiko Uematsu ◽  
Yasunari Tozaki
Keyword(s):  
Aluminum Alloy ◽  
Strain Rate ◽  
Friction Stir Processing ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Cast Aluminum Alloy ◽  
Cast Aluminum ◽  
Rate Condition ◽  
Friction Stir ◽  
Strain Rate Condition

The fatigue behavior of cast aluminum alloy, A356-T6, microstructurally modified by the friction stir processing (FSP) was investigated. The FSP conditions were set to be the tool rotational speed of 500 rpm and traveling speed of 200 mm/min, in which the strain rate was relatively low. Plane bending fatigue tests have been performed using the as-cast and friction stir processed (FSPed) specimens. Fatigue strengths in the finite life region and the fatigue limit of the FSPed specimens were highly improved compared with the as-cast ones resulting from the elimination of casting defects by the FSP. However, the crack growth rates of the FSPed specimens were faster than those of the as-cast ones due to the softening of the material by heat input during the FSP. The effects of FSP with low stain rate were discussed based on the microstructural consideration.

The Modified Rate Approach Method to Evaluate Fatigue Life Under Synchronously Changing Temperature and Strain Rate in Elevated Temperature Water

2002 ◽  
Author(s):  
Kazuya Tsutsumi ◽  
Makoto Higuchi ◽  
Kunihiro Iida ◽  
Yutaka Yamamoto
Keyword(s):  
Fatigue Life ◽  
Elevated Temperature ◽  
Strain Rate ◽  
Constant Strain Rate ◽  
Environmental Water ◽  
Transient Condition ◽  
Strain Rate Change ◽  
Rate Condition ◽  
Approach Method ◽  
Temperature Water

The fatigue life of steel in elevated temperature water is strongly affected by the composition of the environmental water, temperature and strain rate. The effects of these parameters on fatigue life reduction have been investigated experimentally in these years. One problem to be discussed is the fact that the previous experiments which leaded main conclusions on the environmental effects were generally executed by keeping a set of experimental parameters constant. In the transient condition in an actual plant, however, such parameters as temperature and strain rate are not constant. In order to evaluate fatigue damage in an actual plant on the basis of experimental results under constant temperature and constant strain rate conditions, the modified rate approach method was developed. The method can be applicable to changing temperature condition and strain rate condition separately. In the present study, an additional model is proposed with considering that both temperature and strain rate change simultaneously in an actual plant. The applicability of this method is discussed and verified experimentally. The fatigue lives predicted by this method are scattered within the factor of 2 or 3 bands against test results even when several parameters changed synchronously.

Applicability of the Modified Rate Approach Method Under Various Conditions Simulating Actual Plant Conditions

2006 ◽  
Author(s):  
Katsumi Sakaguchi ◽  
Yuichiro Nomura ◽  
Shigeki Suzuki ◽  
Hiroshi Kanasaki
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Fatigue Tests ◽  
Transient Condition ◽  
Stress Cycle ◽  
Rate Condition ◽  
Approach Method ◽  
Strain Rate Condition ◽  
Fatigue Evaluation ◽  
Fatigue Life Reduction

The fatigue life in elevated temperature water is strongly affected by water chemistry, temperature and strain rate. The effects of these parameters on fatigue life reduction have been investigated experimentally. In transient condition in an actual plant, however, such parameters as temperature and strain rate are not constant. In order to evaluate fatigue damage in actual plant on the basis of experimental results under constant temperature and strain rate condition, the modified rate approach method was developed. As a part of the EFT (Environmental Fatigue Tests) project, the study was conducted in order to evaluate the applicability of the modified rate approach to the case where temperature and strain rate varied simultaneously. It was reported in the previous papers (1,2) that the accuracy of modified rate approach is about factor of 2. Various kinds of transient have to be taken into account of in actual plant fatigue evaluation, and stress cycle of several ranges of amplitude has to be considered in assessing damage from fatigue. Generally, cumulative usage factor is applied in this type of evaluation. In this study, in order to confirm applicability of modified rate approach method together with cumulative usage factor, tests were carried out by combining stress cycle blocks of different strain amplitude levels, in which temperature changes in response to strain change in a simulated PWR environment.

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