Editorial

3 pages, 153 KiB

Open AccessEditorial

Deformation Behavior of the Alloys under Simple and Combined Loading Conditions at Various Deformation Rate

by Takeshi Iwamoto and Tao Suo

Metals 2018, 8(9), 733; https://doi.org/10.3390/met8090733 - 18 Sep 2018

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Clarifying the mechanical behavior of alloys is quite important to enhance their performance
and thus expand their application in various fields. [...]
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(This article belongs to the Special Issue Deformation Behavior of the Alloys under Simple and Combined Loading Conditions at Various Deformation Rate)

Research

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16 pages, 5669 KiB

Open AccessArticle

Finite Element Analysis on a Newly-Modified Method for the Taylor Impact Test to Measure the Stress-Strain Curve by the Only Single Test Using Pure Aluminum

by Chong Gao and Takeshi Iwamoto

Metals 2018, 8(8), 642; https://doi.org/10.3390/met8080642 - 15 Aug 2018

Cited by 15 | Viewed by 5001

Abstract

In this study, finite element analyses are performed to obtain a stress-strain curve for ductile materials by a combination between the distributions of axial stress and strain at a certain time as a result of one single Taylor impact test. In the modified [...] Read more.

In this study, finite element analyses are performed to obtain a stress-strain curve for ductile materials by a combination between the distributions of axial stress and strain at a certain time as a result of one single Taylor impact test. In the modified Taylor impact test proposed here, a measurement of the external impact force by the Hopkinson pressure bar placed instead of the rigid wall, and an assumption of bi-linear distribution of an axial internal force, are introduced as well as a measurement of deformed profiles at certain time. In order to obtain the realistic results by computations, at first, the parameters in a nonlinear rate sensitive hardening law are identified from the quasi-static and impact tests of pure aluminum at various strain rates and temperature conducted. In the impact test, a miniaturized testing apparatus based on the split Hopkinson pressure bar (SHPB) technique is introduced to achieve a similar level of strain rate as 10⁴ s⁻¹, to the Taylor test. Then, a finite element simulation of the modified test is performed using a commercial software by using the user-subroutine for the hardening law with the identified parameters. By comparing the stress-strain curves obtained by the proposed method and direct calculation of the hardening law, the validity is discussed. Finally, the feasibility of the proposed method is studied. Full article

(This article belongs to the Special Issue Deformation Behavior of the Alloys under Simple and Combined Loading Conditions at Various Deformation Rate)

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15 pages, 12212 KiB

Open AccessArticle

Strain Rate Dependence of Material Strength in AA5xxx Series Aluminum Alloys and Evaluation of Their Constitutive Equation

by Hiroyuki Yamada, Tsuyoshi Kami, Ryota Mori, Tomoyuki Kudo and Minemitsu Okada

Metals 2018, 8(8), 576; https://doi.org/10.3390/met8080576 - 25 Jul 2018

Cited by 33 | Viewed by 6107

Abstract

The effect of strain rate on the mechanical properties of AA5xxx series aluminum alloys containing solute Mg atoms (AA5005, AA5021, AA5082 and AA5182) and pure aluminum (A1070) was investigated within a wide strain rate range of 1.0 × 10⁻⁴ to 1.0 × [...] Read more.

The effect of strain rate on the mechanical properties of AA5xxx series aluminum alloys containing solute Mg atoms (AA5005, AA5021, AA5082 and AA5182) and pure aluminum (A1070) was investigated within a wide strain rate range of 1.0 × 10⁻⁴ to 1.0 × 10³ s⁻¹ at room temperature. The A1070 exhibited a positive strain rate dependence of material strength at the investigated strain rates. However, the AA5xxx series aluminum alloys primarily exhibited the negative strain rate dependence of material strength and serration caused by the Portevin-Le Chatelier effect on the Mg content and strain rate. As a result of using the material constitutive equation for the negative strain rate dependence, it was found that the flow stress may change in the dynamic strain rate range. However, it was found that the strain rate dependence of material strength differed in the AA5082 and the AA5182 alloys. It would be caused by less solute Mg of the Al phase in the AA5182 alloy than in the AA5082 alloy, because more Mg₂Si compounds precipitated on Mn bearing particles as precipitation sites in the AA5182 alloy. Full article

(This article belongs to the Special Issue Deformation Behavior of the Alloys under Simple and Combined Loading Conditions at Various Deformation Rate)

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20 pages, 10902 KiB

Open AccessArticle

Influence of Stress State on the Mechanical Impact and Deformation Behaviors of Aluminum Alloys

by Marcos Rodriguez-Millan, Daniel Garcia-Gonzalez, Alexis Rusinek and Angel Arias

Metals 2018, 8(7), 520; https://doi.org/10.3390/met8070520 - 05 Jul 2018

Cited by 39 | Viewed by 6442

Abstract

Under impact loading conditions, the stress state derived from the contact between the projectile and the target, as well as from the subsequent mechanical waves, is a variable of great interest. The geometry of the projectile plays a dertermining role in the resulting [...] Read more.

Under impact loading conditions, the stress state derived from the contact between the projectile and the target, as well as from the subsequent mechanical waves, is a variable of great interest. The geometry of the projectile plays a dertermining role in the resulting stress state in the targeted structure. In this regard, different stress states lead to different failure modes. In this work, we analyze the influence of the stress state on the deformation and failure behaviors of three aluminum alloys that are commonly used in the aeronautical, naval, and automotive industries. To this purpose, tension-torsion tests are performed covering a wide range of stress triaxialities and Lode parameters. Secondly, the observations from these static tests are compared to failure mode of the same materials at high impact velocities tests with the aim of analysing the role of stress state and strain rate in the mechanical response of the aluminum plates. Experimental impacts are conducted with different projectile geometries to allow for the analysis of stress states influence. In addition, these experiments are simulated by using finite element models to evaluate the predictive capability of three failure criteria: critical plastic deformation, Johnson-Cook, and Bai-Wierzbicki. Full article

(This article belongs to the Special Issue Deformation Behavior of the Alloys under Simple and Combined Loading Conditions at Various Deformation Rate)

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17 pages, 16575 KiB

Open AccessArticle

Enhancement of Strength and Hot Workability of AZX312 Magnesium Alloy by Disintegrated Melt Deposition (DMD) Processing in Contrast to Permanent Mold Casting

by Kamineni Pitcheswara Rao, Kalidass Suresh, Yellapregada Venkata Rama Krishna Prasad, Norbert Hort and Manoj Gupta

Metals 2018, 8(6), 437; https://doi.org/10.3390/met8060437 - 08 Jun 2018

Cited by 7 | Viewed by 2960

Abstract

AZX312 (AZ31-2Ca) magnesium alloy, with starting conditions of as-cast (AC), cast-homogenized (CH), and disintegrated melt deposition (DMD), is examined in terms of its compressive strength and hot working behavior to establish the relative merits and limitations of these processing routes. Processing maps are [...] Read more.

AZX312 (AZ31-2Ca) magnesium alloy, with starting conditions of as-cast (AC), cast-homogenized (CH), and disintegrated melt deposition (DMD), is examined in terms of its compressive strength and hot working behavior to establish the relative merits and limitations of these processing routes. Processing maps are developed in the temperature range of 300–500 °C and strain rate range of 0.0003–10 s⁻¹, and mechanisms of hot deformation are established based on microstructures, tensile ductility, and activation parameters. The alloy in AC and CH conditions has a large grain size with intermetallic phases at the grain boundaries and in the matrix. In DMD processed alloy, the grain size is very small and the phases are refined and distributed uniformly. The compressive strength is significantly improved by DMD processing, which is attributed to the grain refinement. The processing maps for AC and CH conditions are similar, exhibiting only a single workability domain, while the DMD processed alloy exhibited three domains that enhanced workability. The additional workability domain at higher strain rates is an advantage in designing forming processes that facilitates faster production, while the fine grain size produced by a finishing operation in the lower temperature domain will improve the mechanical properties of the product. Full article

(This article belongs to the Special Issue Deformation Behavior of the Alloys under Simple and Combined Loading Conditions at Various Deformation Rate)

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12 pages, 5455 KiB

Open AccessArticle

A New Experimental and Numerical Framework for Determining of Revised J-C Failure Parameters

by Cunxian Wang, Tao Suo, Yulong Li, Pu Xue and Zhongbin Tang

Metals 2018, 8(6), 396; https://doi.org/10.3390/met8060396 - 30 May 2018

Cited by 14 | Viewed by 3137

Abstract

Since damage evolutions of materials play important roles in simulations, such as ballistic impacts and collisions, a new experimental and numerical method is established to determine the revised Johnson–Cook (JC) failure parameters of a 2618 aluminum alloy and a Ti-6Al-4V titanium alloy. Not [...] Read more.

Since damage evolutions of materials play important roles in simulations, such as ballistic impacts and collisions, a new experimental and numerical method is established to determine the revised Johnson–Cook (JC) failure parameters of a 2618 aluminum alloy and a Ti-6Al-4V titanium alloy. Not only the strain distributions, but also the stress triaxialities of designed specimens with different notches, are analyzed and revised using the finite element (FE) model. Results show that the largest strain concentrated on the surface of the circumferential area where the initial damage happened, which coincided with the practical damage evolution in the FE model. The complete damage strain, which denoted the largest strain before fracture calculated by the picture, is put forward to replace the traditional failure strain. Consequently, the digital image correlation (DIC) method and the micro speckle are carried out to measure the complete strain from the circumferential area. In addition, the relationships between the complete damage strain, the revised stress triaxiality, the strain rate and the temperature are established by conducting the quasi-static and dynamic experiments under different temperatures. Finally, the simulations for the ballistic impact tests are conducted to validate the accuracy of the parameters of the revised JC damage model. Full article

(This article belongs to the Special Issue Deformation Behavior of the Alloys under Simple and Combined Loading Conditions at Various Deformation Rate)

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15 pages, 4880 KiB

Open AccessArticle

Scaling Law in Laser-Induced Shock Effects of NiTi Shape Memory Alloy

by Xi Wang, Weiguang Xia, Xianqian Wu and Chenguang Huang

Metals 2018, 8(3), 174; https://doi.org/10.3390/met8030174 - 10 Mar 2018

Cited by 3 | Viewed by 3431

Abstract

The shock effects in laser shock processing of NiTi shape memory alloy were studied by dimensional analysis and finite element simulation. The essential dimensionless parameters controlling the residual stress distribution and plastically affected depth were found to be dimensionless pressure duration and peak [...] Read more.

The shock effects in laser shock processing of NiTi shape memory alloy were studied by dimensional analysis and finite element simulation. The essential dimensionless parameters controlling the residual stress distribution and plastically affected depth were found to be dimensionless pressure duration and peak pressure. By adopting the constitutive model considering the martensitic transformation and plasticity of deformation induced martensite, the influence of dimensionless parameters on the shock effects of shape memory alloy was studied numerically. The numerical results reveal the scaling law of shock effects on those dimensionless parameters quantitatively and the relationship between the plastically affected depth and peak pressure was validated with experimental results. A window of the optimal processing parameters could be obtained based on this study. Full article

(This article belongs to the Special Issue Deformation Behavior of the Alloys under Simple and Combined Loading Conditions at Various Deformation Rate)

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10 pages, 5297 KiB

Open AccessArticle

An Investigation on the Adiabatic Shear Bands in Depleted U-0.75 wt % Ti Alloy under Dynamic Loading

by Bo Wang, Yongxiang Dong and Guangyan Huang

Metals 2018, 8(2), 145; https://doi.org/10.3390/met8020145 - 22 Feb 2018

Cited by 7 | Viewed by 5944

Abstract

Adiabatic shear bands in uranium alloy projectiles/penetrators, during penetration, allow them to “self-sharpen,” a process that is absent in most tungsten alloy projectiles/penetrators. U-0.75 wt % Ti alloy samples have been accelerated to impact steel targets, and the distribution of adiabatic shear bands [...] Read more.

Adiabatic shear bands in uranium alloy projectiles/penetrators, during penetration, allow them to “self-sharpen,” a process that is absent in most tungsten alloy projectiles/penetrators. U-0.75 wt % Ti alloy samples have been accelerated to impact steel targets, and the distribution of adiabatic shear bands in residual samples has been studied in detail to understand the effect of self-sharpening on penetration. In our study, self-sharpening was evidenced by the distribution of the shear bands in the recovered sample. The shear bands formed during impact were observed to change direction when they crossed grain boundaries, which indicated that the grain boundaries had an influence on the adiabatic shear bands of U-0.75 wt % Ti. Micro-hardness test results showed that the Vickers micro-hardness in the adiabatic shear zone was 18% lower than that in the matrix. In the split-Hopkinson pressure bar (SHPB) experiment, a strain rate of around 2891 s⁻¹ was the threshold strain rate that triggered the formation of adiabatic shear bands in the U-0.75 wt % Ti alloy. Full article

(This article belongs to the Special Issue Deformation Behavior of the Alloys under Simple and Combined Loading Conditions at Various Deformation Rate)

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6001 KiB

Open AccessArticle

Strain Rate Effect on Tensile Behavior for a High Specific Strength Steel: From Quasi-Static to Intermediate Strain Rates

by Wei Wang, Yan Ma, Muxin Yang, Ping Jiang, Fuping Yuan and Xiaolei Wu

Metals 2018, 8(1), 11; https://doi.org/10.3390/met8010011 - 29 Dec 2017

Cited by 51 | Viewed by 12833

Abstract

The strain rate effect on the tensile behaviors of a high specific strength steel (HSSS) with dual-phase microstructure has been investigated. The yield strength, the ultimate strength and the tensile toughness were all observed to increase with increasing strain rates at the range [...] Read more.

The strain rate effect on the tensile behaviors of a high specific strength steel (HSSS) with dual-phase microstructure has been investigated. The yield strength, the ultimate strength and the tensile toughness were all observed to increase with increasing strain rates at the range of 0.0006 to 56/s, rendering this HSSS as an excellent candidate for an energy absorber in the automobile industry, since vehicle crushing often happens at intermediate strain rates. Back stress hardening has been found to play an important role for this HSSS due to load transfer and strain partitioning between two phases, and a higher strain rate could cause even higher strain partitioning in the softer austenite grains, delaying the deformation instability. Deformation twins are observed in the austenite grains at all strain rates to facilitate the uniform tensile deformation. The B2 phase (FeAl intermetallic compound) is less deformable at higher strain rates, resulting in easier brittle fracture in B2 particles, smaller dimple size and a higher density of phase interfaces in final fracture surfaces. Thus, more energy need be consumed during the final fracture for the experiments conducted at higher strain rates, resulting in better tensile toughness. Full article

(This article belongs to the Special Issue Deformation Behavior of the Alloys under Simple and Combined Loading Conditions at Various Deformation Rate)

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