A quantitative criterion for predicting solid-state disordering during biaxial, high strain rate deformation

2021 ◽  
Author(s):  
Michael Becker ◽  
Desiderio Kovar
Keyword(s):  
Stress State ◽  
Strain Rate ◽  
Strain State ◽  
Biaxial Loading ◽  
High Strain ◽  
Md Simulations ◽  
Strain Rates ◽  
Critical Strain Rate ◽  
Wide Range ◽  
High Strain Rate Deformation

Abstract A criterion to predict the onset of disordering under biaxial loading based on a critical potential energy per atom was studied. In contrast to previous theories for disordering, this criterion incorporates the effects of strain rate and strain state. The strain state (or stress state) is defined by the combination of strain (or stress) magnitudes and directions that are applied to each sample during the simulation. Τhe validity of this criterion was studied using molecular dynamic (MD) simulations of Ag conducted over a wide range of biaxial strain rates, strain configurations, and crystal orientations with respect to the applied stress state. Biaxial strains were applied in two different planes, (112 ̅) and (001) in eight directions in each plane. Results showed that, when larger strain rates were applied, there was a transition from plastic deformation driven by the nucleation and propagation of dislocations to disordering and viscous flow. Although the critical strain rate to initiate disorder was found to vary in the range of ε ̇ = 1×1011 s-1 to ε ̇ = 4×1011 s-1, a consistent minimum PE/atom of -2.7 eV was observed over a broad range of strain states and for both crystallographic orientations that were studied. This indicates that the critical PE/atom is a material property that can be used to predict the onset of disordering under biaxial loading. Further, the results showed that this criterion can be applied successfully even when non-uninform strain states arise in the crystal.  

High Strain-Rate Compressive Behavior and Constitutive Modeling of Selected Polymers Using Modified Ramberg-Osgood Equation

2014 ◽  
Vol 566 ◽  
pp. 80-85
Author(s):  
Kenji Nakai ◽  
Takashi Yokoyama
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Compressive Stress ◽  
Constitutive Modeling ◽  
High Strain ◽  
Strain Rates ◽  
Stress Strain ◽  
Strain Behavior ◽  
Least Squares Fit ◽  
Wide Range

The present paper is concerned with constitutive modeling of the compressive stress-strain behavior of selected polymers at strain rates from 10-3 to 103/s using a modified Ramberg-Osgood equation. High strain-rate compressive stress-strain curves up to strains of nearly 0.08 for four different commercially available extruded polymers were determined on the standard split Hopkinson pressure bar (SHPB). The low and intermediate strain-rate compressive stress-strain relations were measured in an Instron testing machine. Six parameters in the modified Ramberg-Osgood equation were determined by fitting to the experimental stress-strain data using a least-squares fit. It was shown that the monotonic compressive stress-strain behavior over a wide range of strain rates can successfully be described by the modified Ramberg-Osgood constitutive model. The limitations of the model were discussed.

High Strain Rate Mechanical Properties of SAC-Q Between -65°C and +200°C After Exposure to Isothermal Aging

2020 ◽  
Author(s):  
Pradeep Lall ◽  
Vishal Mehta ◽  
Jeff Suhling ◽  
Ken Blecker
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Isothermal Aging ◽  
High Strain ◽  
Strain Rates ◽  
Solder Alloys ◽  
Stress Strain ◽  
Wide Range ◽  
Operating Temperatures ◽  
Electronic Parts

Abstract In many industries, such as automotive, oil and gas, aerospace, medical technologies, electronic parts can often be exposed to high strain loads during shocks, vibrations and drop-impact conditions. Such electronic parts can often be subjected to extreme low and high temperatures ranging from −65°C to 200°C. Also, these electronic devices can be subjected to strain rates of 1 to 100 per second in the critical environment. Recently, many doped SAC solder alloys are being introduced in the electronic component including SAC-Q, SAC-R, Innolot. SAC-Q is made with addition of Bi in Sn-Ag-Cu composition. Mechanical characteristic results and data for lead-free solder alloys are extremely important for optimizing electronic package reliability, at high temperature storage and elevated strain rates. Furthermore, the mechanical properties of solder alloys can be changed significantly due to a thermal aging, which is causing modification of microstructure. Data for the SAC-Q solder alloy with a high temp aging and testing at extreme low to high operating temperatures are not available. SAC-Q material was tested and analyzed for this study at range of operating temperatures of −65°C to 200°C and at a strain rate up to 75 per second. After the specimens were manufactured and reflowed, specimens were stored at 100°C for the isothermal aging for up to 90 days, before tensile tests were carried out at different operating temperatures. For the wide range of strain rates and test temperatures, stress-strain curves are established. In addition, the measured experimental results and data were fitted to the Anand viscoplasticity model and the Anand constants were calculated by estimating the stress-strain behavior measured in the wide range of operating temperatures and strain rates.

Mechanical Properties of Doped Solder SAC-Q for High Strain Rate Testing at Extreme Surrounding Temperatures for 6 Months of Isothermal Aging

2021 ◽  
Author(s):  
Pradeep Lall ◽  
Vishal Mehta ◽  
Jeff Suhling ◽  
Ken Blecker
Keyword(s):  
High Temperature ◽  
High Strain Rate ◽  
Strain Rate ◽  
Isothermal Aging ◽  
High Strain ◽  
Thermal Exposure ◽  
Strain Rates ◽  
Strain Behavior ◽  
Wide Range ◽  
Electronic Parts

Abstract Electronic parts may often get exposed to high strains during shocks, vibrations and drop conditions in both commercial and defense applications. In addition, such electronic parts can often be simultaneously exposed to extreme surrounding temperatures between −65°C and 200°C after storage in non-climate-controlled conditions. Electronic equipment can be subjected to strain rates of 1 to 100 per second in shock and vibration. Many of the doped SAC soldering alloys in the electronic components, including SAC-Q, SAC-R, Innolot have found applications in long-term thermal exposure environments. Low temperature high strain-rate properties are needed to assure durability under high temperature storage followed by shock and vibration. There is scarcity of high strain-rate data on alloys exposed to high temperature aging operating at extreme low-temperatures and extremely-high temperatures. For this study, SAC-Q material was tested and analyzed at temperatures from −65°C to 200°C and at a strain rates of from 10 to 75 per second. Following the production and retrieval of the specimens, specimens were stored for isothermal aging for up to 6 months at 100°C temperature, before performing tensile test experiments at various operating temperatures. Stress vs strain curves are formed for the wide range of strain rates and surrounding temperatures. In addition, test results and data were complemented by the Anand viscoplasticity model and by calculating stress-strain behavior, evaluated in a wide range of working temperatures and strains rates.

scholarly journals Large Strain Mechanical Behavior of HSLA-100 Steel Over a Wide Range of Strain Rates

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Maen Alkhader ◽  
Laurence Bodelot
Keyword(s):  
Strain Rate ◽  
High Strain ◽  
Large Strain ◽  
Cold Work ◽  
High Strength ◽  
Adiabatic Shear ◽  
Strain Rates ◽  
Plastic Energy ◽  
Wide Range ◽  
Constitutive Response

High-strength low alloy steels (HSLA) have been designed to replace high-yield (HY) strength steels in naval applications involving impact loading as the latter, which contain more carbon, require complicated welding processes. The critical role of HSLA-100 steel requires achieving an accurate understanding of its behavior under dynamic loading. Accordingly, in this paper, we experimentally investigate its behavior, establish a model for its constitutive response at high-strain rates, and discuss its dynamic failure mode. The large strain and high-strain-rate mechanical constitutive behavior of high strength low alloy steel HSLA-100 is experimentally characterized over a wide range of strain rates, ranging from 10−3 s−1 to 104 s−1. The ability of HSLA-100 steel to store energy of cold work in adiabatic conditions is assessed through the direct measurement of the fraction of plastic energy converted into heat. The susceptibility of HSLA-100 steel to failure due to the formation and development of adiabatic shear bands (ASB) is investigated from two perspectives, the well-accepted failure strain criterion and the newly suggested plastic energy criterion [1]. Our experimental results show that HSLA-100 steel has apparent strain rate sensitivity at rates exceeding 3000 s−1 and has minimal ability to store energy of cold work at high deformation rate. In addition, both strain based and energy based failure criteria are effective in describing the propensity of HSLA-100 steel to dynamic failure (adiabatic shear band). Finally, we use the experimental results to determine constants for a Johnson-Cook model describing the constitutive response of HSLA-100. The implementation of this model in a commercial finite element code gives predictions capturing properly the observed experimental behavior. High-strain rate, thermomechanical processes, constitutive behavior, failure, finite elements, Kolsky bar, HSLA-100.

BRITTLE FRAGMENTATION OF AN EXPANDING RING BY MOLECULAR DYNAMICS

2013 ◽  
Vol 02 (02) ◽  
pp. 1350010
Author(s):  
GUOWU REN ◽  
TIEGANG TANG ◽  
ZHAOLIANG GUO ◽  
YUANSHUAI YANG ◽  
QINGZHONG LI
Keyword(s):  
Strain Rate ◽  
Physical Mechanism ◽  
High Strain ◽  
Fragmentation Process ◽  
Strain Rates ◽  
Anisotropic Behavior ◽  
Wide Range ◽  
Low Strain Rate ◽  
Brittle Fragmentation ◽  
Random Defect

In this paper, the brittle fragmentation of an expanding ring is numerically studied by a simple atomistic model. We investigate the statistical distribution of fragment spanned over a wide range of strain rates when damage related to broken bond reaches a steady state. It is shown that at low strain rate limited number of heavy fragments can be generated because of anisotropic behavior while for high strain rate fragment can be well fitted with Weibull distribution. The physical mechanism of fragmentation process reveals that damage accompanying with numerous microcracks is found to initiate in the inner regime of the expanding ring. Furthermore, we discuss the effect of random defect on the fragmentation process.

scholarly journals Intermediate Strain Rate Testing Devices

2020 ◽  
Author(s):  
Trunal Bhujangrao
Keyword(s):  
Experimental Data ◽  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Full Range ◽  
Strain Rates ◽  
Intermediate Strain Rate ◽  
Wide Range ◽  
Rate Testing ◽  
Rate Test

The existing experimental tests are mainly designed to study the mechanical response of materials at various strain rates. Many researchers performed the experimental test in tension, compression, and shear (with torsion test) over a wide range of strain rates. They found out that material exhibits an increase in yield stress as well as flows stress with an increase in strain rate. It illustrates that there is a need for experimental data to study the material behaviour over the full range of strain rates, from quasi-static to high strain rate test. Many special techniques have been developed to bridge the strain rate gap between quasi-static and high strain rate testing to provide a method for an intermediate strain rate test for engineering materials. Some researchers have tried to conduct intermediate strain rate tests with standard servo-hydraulic load frames. However, the results of such tests are not accurate. The problem is that during the experiment, the whole machine is not in static equilibrium. The inertial effect influences the experimental data. The records obtained from these machines are often noisy with large oscillation. therefore, the comprehensive review is given to describes the development and evolution of the existing intermediate strain rate testing devices which includes the working principles, some critical theories, technological innovation in load measurement techniques, components of the device, basic technical assumption, and measuring techniques. In addition, some research direction on future implementation and development of an intermediate strain rate apparatus is also discussed in detail.

scholarly journals Plane strain tension fracture at high strain rate

2021 ◽  
Vol 250 ◽  
pp. 01020
Author(s):  
Morwan Adlafi ◽  
Bertrand Galpin ◽  
Laurent Mahéo ◽  
Christian C. Roth ◽  
Dirk Mohr ◽  
...  
Keyword(s):  
Stress State ◽  
High Strain Rate ◽  
Strain Rate ◽  
Plane Strain ◽  
High Strain ◽  
Tension Stress ◽  
Outer Diameter ◽  
Strain Rates ◽  
High Strain Rates ◽  
Plane Strain Tension

Under plane stress conditions, most micromechanical and phenomenological models predict a minimum in ductility for plane strain tension stress state. Therefore, the stress state of plane strain tension plays a crucial role in many forming and crash applications and the reliable measurement of the strain to fracture for plane strain tension is particularly crucial when calibrating modern fracture initiation models. Recently, a new experimental technique has been proposed for measuring the strain to fracture for sheet metal after proportional loading under plane strain conditions. The basic configuration of the new setup includes a dihedral punch which applies out-of-plane loading onto a Nakazima-type of discshaped specimen with two symmetric holes and an outer diameter of 60 mm. In the present work, the applicability of the test is extended to high strain rates. High strain rates of about 100/s to 200/s are obtained using a drop weight tower device with an original sensor for load measurements. Quasi static tests are also performed for comparison, keeping the same specimen geometry, image recording parameters and set-up. The effective strains at fracture are compared from quasi-static to high strain rate loading for three different materials, i.e one aluminium alloy and two steels.

High Strain-Rate Constitutive Behavior of SAC305 Solder During Operation at High Temperature

2014 ◽  
Author(s):  
Pradeep Lall ◽  
Di Zhang ◽  
Vikas Yadav
Keyword(s):  
Strain Rate ◽  
High Strain ◽  
Tensile Tests ◽  
Image Correlation ◽  
Dynamic Strain ◽  
Uniaxial Tensile ◽  
Strain Rates ◽  
High Strain Rates ◽  
Wide Range ◽  
Thermal Chamber

Leadfree solders have been used as interconnects in electronic packaging, due to its environmental friendly chemical property. However, those materials may experience high strain rates when subjected to shock and vibration. Consequently, failure will occur to electronics in those situations. Therefore, knowing the material properties of lead-free solders are extremely important, but research on mechanical behaviors of those solder alloys at high strain rates are scarce. Anand’s viscoplastic constitutive model has been widely used to describe the inelastic deformation behavior of solders in electronic components under thermo-mechanical deformation. However, Anand’s model constants for the transient dynamic strain rates are scarce. In this paper, the nine material parameters to fit the Anand viscoplastic model at high strain rates have been presented. In order to develop the constants for this model, uniaxial tensile tests at several strain rates and temperatures have been completed. A constant strain rate impact hammer which enables attaining strain rates around 1 to 100 per sec has been employed to implement tensile tests and a small thermal chamber is applied to control testing temperature. High speed cameras operating at 70,000 fps have been used to capture images of specimen and then digital image correlation method is used to calculate tensile strain. Uniaxial stress-strain curves have been plotted over a wide range of strain rates (ε̇ = 10, 35, 50, 75 /sec) and temperatures (T = 25, 50, 75, 100, 125°C). Anand viscoplasticity constants have been calculated by nonlinear fitting procedures. In addition, the accuracy of the extracted Anand constants has been evaluated by comparing the model prediction and experimental data.

scholarly journals Fully Atomistic Molecular Dynamics Computation of Physico-Mechanical Properties of PB, PS, and SBS

Nanomaterials ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 1088 ◽  
Author(s):  
Yang Kang ◽  
Dunhong Zhou ◽  
Qiang Wu ◽  
Fuyan Duan ◽  
Rufang Yao ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Strain Rate ◽  
Strain Hardening ◽  
Md Simulation ◽  
Md Simulations ◽  
Strain Rates ◽  
Young’S Moduli ◽  
Plastic Modulus ◽  
Styrene Butadiene ◽  
Butadiene Styrene

The physical properties—including density, glass transition temperature (Tg), and tensile properties—of polybutadiene (PB), polystyrene (PS) and poly (styrene-butadiene-styrene: SBS) block copolymer were predicted by using atomistic molecular dynamics (MD) simulation. At 100 K, for PB and SBS under uniaxial tension with strain rate ε ˙ = 1010 s−1 and 109 s−1, their stress–strain curves had four features, i.e., elastic, yield, softening, and strain hardening. At 300 K, the tensile curves of the three polymers with strain rates between 108 s−1 and 1010 s−1 exhibited strain hardening following elastic regime. The values of Young’s moduli of the copolymers were independent of strain rate. The plastic modulus of PS was independent of strain rate, but the Young’s moduli of PB and SBS depended on strain rate under the same conditions. After extrapolating the Young’s moduli of PB and SBS at strain rates of 0.01–1 s−1 by the linearized Eyring-like model, the predicted results by MD simulations were in accordance well with experimental results, which demonstrate that MD results are feasible for design of new materials.

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