scholarly journals Investigation on the Effects of Prefabricated Crack and Strain Rate on Uniaxial Compressive Properties of Frozen Silty Soil

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Dongdong Ma ◽  
Ezra Esanju Kaunda ◽  
Kun Huang
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Shear Failure ◽  
Rapid Change ◽  
Stress Wave Propagation ◽  
Peak Strain ◽  
Soil Specimen ◽  
Silty Soil ◽  
Fracturing Process ◽  
Deformation Properties

To investigate the uniaxial compressive strength and deformation properties of frozen silty soil with prefabricated crack under various strain rates, the static uniaxial compressive tests were conducted for frozen silty soil using three kinds of binder materials to select the suitable prefabricated crack manufacturing method. Afterward, the static and dynamic stress-strain curves of frozen silty soil with different prefabricated crack numbers were obtained based on static and splitting Hopkinson pressure bar (SHPB) tests. In addition, the high-speed camera was employed to record the fracturing process of frozen silty soil under impact loads. Results indicated that the frozen silty soil specimens with no binder showed higher static strength compared with other two binder materials (plaster and Vaseline). The strength growth rate of frozen silty soil showed three-stage (fast-slow-rapid) change characteristics. The peak strain of frozen silty soil under static loads scope was higher compared with that under dynamic loads, while its dynamic peak strain with various prefabricated crack numbers was remarkably rate-dependent. The absorbed energy density of frozen silty soil was subject to a negative (positive) relationship with the prefabricated crack numbers (strain rate). The dominated crack of intact frozen silty soil specimen finally presented Y-shaped shear failure. However, tensile cracks parallel to stress wave propagation direction were observed for the frozen silty soil specimen with prefabricated crack.

The Effect of Strain Rate on the Material Characteristics of Nickel-Based Superalloy Inconel 718

2007 ◽  
Vol 340-341 ◽  
pp. 283-288 ◽  
Author(s):  
Jung Han Song ◽  
Hoon Huh
Keyword(s):  
Dynamic Response ◽  
High Strain Rate ◽  
Strain Rate ◽  
Turbine Blade ◽  
Inconel 718 ◽  
High Speed ◽  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
Experimental Results ◽  
Stress Wave Propagation

The dynamic response of the turbine blade materials is indispensable for analysis of erosions of turbine blades as a result of impulsive loading associated with gas flow. This paper is concerned with the dynamic material properties of the Inconel 718 alloy which is widely used in the high speed turbine blade. The dynamic response at the corresponding level of the strain rate should be acquired with an adequate experimental technique and apparatus due to the inertia effect and the stress wave propagation. In this paper, the dynamic response of the Inconel 718 at the intermediate strain rate ranged from 1/s to 400/s is obtained from the high speed tensile test and that at the high strain rate above 1000/s is obtained from the split Hopkinson pressure bar test. The effects of the strain rate on the dynamic flow stress, the strain rate sensitivity and the failure elongation are evaluated with the experimental results. Experimental results from both the quasi-static and the high strain rate up to 3000/s are interpolated in order to construct the constitutive relation that should be applied to simulate the dynamic behavior of the turbine blade made of the Inconel 718.

Dynamic Friction Measurements at Sliding Velocities Representative of High-Speed Machining Processes

2000 ◽  
Vol 122 (4) ◽  
pp. 834-848 ◽  
Author(s):  
H. D. Espinosa ◽  
A. J. Patanella ◽  
M. Fischer
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Experimental Methodology ◽  
Stress Wave Propagation ◽  
Fracture Mechanisms ◽  
Dynamic Friction ◽  
High Speed Machining ◽  
Machining Processes ◽  
Friction Coefficients ◽  
Al 6061

Understanding high speed machining processes requires knowledge of the dynamic friction response at the tool-workpiece interface, the high strain rate response of the workpiece material and its fracture mechanisms. In this paper, a novel experimental technique, consisting in the independent application of an axial static load and a dynamic torque, is used to investigate time resolved dynamic friction. Shear stress wave propagation along an input bar, pressing statically against an output bar, is analyzed. The quasi-static and kinetic friction coefficients of Ti-6Al-4V sliding against 1080 Steel, Al 6061-T6 sliding against 1080 Steel, and Al 6061-T6 sliding against Al 7075-T6, with various surface characteristics, are investigated. Sliding velocities up to 6.9 m/s are achieved. Surface roughness is varied to understand its role on the frictional response of the sliding interfaces. The dependence of friction coefficient on material strain-rate sensitivity is also assessed. Measured friction coefficients compared well with values reported in the literature using other experimental techniques. The experimental methodology discussed in this article provides a robust method for direct measurement of the quasi-static and dynamic friction coefficients representative of high-speed machining, metal-forming and ballistic penetration processes. [S0742-4787(00)01304-7]

Failure Site Transition During Drop Testing of Printed Wiring Assemblies

2005 ◽  
Author(s):  
Joseph Varghese ◽  
Bo Song ◽  
Michael H. Azarian ◽  
Abhijit Dasgupta ◽  
Michael Pecht
Keyword(s):  
Strain Rate ◽  
High Speed ◽  
Intermetallic Layer ◽  
Bulk Solder ◽  
Peak Strain ◽  
Strain And Strain Rate ◽  
Plastic Ball ◽  
High Speed Data Acquisition ◽  
Number Of Cycles ◽  
Failure Site

This paper reports on the effect of printed wiring assembly (PWA) flexural strain and strain rate and aging on the durability and failure site of Sn-Pb solders in area array packages. Two different plastic ball grid array (PBGA) package styles, one with a single die and the other with stacked die, are used for this study. We consider the effect of intermetallic growth on the failure site transition in the interconnects. Results are compared to similar studies in literature. This study quantifies durability in terms of the local PWA response (PWA flexural strain, PWA flexural strain rate, cyclic history) instead of the conventional approaches that typically use loading parameters (total impact energy, orientation and number of drops. This makes the results more generic and easier to extrapolate to different assemblies and different loading/orientation conditions. Four point bend tests are conducted on the PWAs assembled with PBGA components. A high speed data acquisition system with in-situ resistance monitoring is used to track the PWA response and the number of cycles to failure. The strain rate is varied over three orders of magnitude while the peak strain is studied over the range of 25 to 75% of the overstress limit. The durability of the specimens decreases with increasing PWA flexural strain and varies non-monotonically with flexural strain rate. As-reflowed samples (with a thin intermetallic layer), undergo a transition in the failure site from bulk solder to FR-4 board and copper trace with increasing PWA flexure. Aged samples (with a thick intermetallic layer), have lower durability and fail in the intermetallic layer for all values of PWA strain. This study identifies the PWA flexural strain and strain rate limits for failure site transition in aged and as-reflowed samples of a PBGA package.

scholarly journals Experimental Study on Biaxial Dynamic Compressive Properties of ECC

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1257
Author(s):  
Shuling Gao ◽  
Guanhua Hu
Keyword(s):  
Strain Rate ◽  
Lateral Pressure ◽  
Deformation Modulus ◽  
Strain Curve ◽  
Peak Stress ◽  
Pressure Level ◽  
Strain Rates ◽  
Peak Strain ◽  
Stress Strain Curve ◽  
Toughness Index

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength applied laterally to the static compressive strength of the specimen), and three strain rates of 10−4, 10−3 and 10−2 s−1. The failure mode, peak stress, peak strain, deformation modulus, stress-strain curve, and compressive toughness index of ECC under biaxial dynamic compressive stress state are obtained. The test results show that the lateral pressure affects the direction of ECC cracking, while the strain rate has little effect on the failure morphology of ECC. The growth of lateral pressure level and strain rate upgrades the limit failure strength and peak strain of ECC, and the small improvement is achieved in elastic modulus. A two-stage ECC biaxial failure strength standard was established, and the influence of the lateral pressure level and peak strain was quantitatively evaluated through the fitting curve of the peak stress, peak strain, and deformation modulus of ECC under various strain rates and lateral pressure levels. ECC’s compressive stress-strain curve can be divided into four stages, and a normalized biaxial dynamic ECC constitutive relationship is established. The toughness index of ECC can be increased with the increase of lateral pressure level, while the increase of strain rate can reduce the toughness index of ECC. Under the effect of biaxial dynamic load, the ultimate strength of ECC is increased higher than that of plain concrete.

scholarly journals Aggravation of functional mitral regurgitation on left ventricle stiffness in type 2 diabetes mellitus patients evaluated by CMR tissue tracking

2021 ◽  
Vol 20 (1) ◽  
Author(s):  
Yi Zhang ◽  
Wei-feng Yan ◽  
Li Jiang ◽  
Meng-ting Shen ◽  
Yuan Li ◽  
...  
Keyword(s):  
Diabetes Mellitus ◽  
Type 2 Diabetes ◽  
Type 2 Diabetes Mellitus ◽  
Mitral Regurgitation ◽  
Strain Rate ◽  
Left Ventricular ◽  
Functional Mitral Regurgitation ◽  
Lv Function ◽  
Peak Strain

Abstract Background Functional mitral regurgitation (FMR) is one of the most common heart valve diseases in diabetes and may increase left ventricular (LV) preload and aggravate myocardial stiffness. This study aimed to investigate the aggravation of FMR on the deterioration of LV strain in type 2 diabetes mellitus (T2DM) patients and explore the independent indicators of LV peak strain (PS). Materials and methods In total, 157 T2DM patients (59 patients with and 98 without FMR) and 52 age- and sex-matched healthy control volunteers were included and underwent cardiac magnetic resonance examination. T2DM with FMR patients were divided into T2DM patients with mild (n = 21), moderate (n = 19) and severe (n = 19) regurgitation. LV function and global strain parameters were compared among groups. Multivariate analysis was used to identify the independent indicators of LV PS. Results The T2DM with FMR had lower LV strain parameters in radial, circumferential and longitudinal direction than both the normal and the T2DM without FMR (all P < 0.05). The mild had mainly decreased peak diastolic strain rate (PDSR) compared to the normal. The moderate had decreased peak systolic strain rate (PSSR) compared to the normal and PDSR compared to the mild and the normal. The severe FMR group had decreased PDSR and PSSR compared to the mild and the normal (all P < 0.05). Multiple linear regression showed that the regurgitation degree was independent associated with radial (β = − 0.272), circumferential (β = − 0.412) and longitudinal (β = − 0.347) PS; the months with diabetes was independently associated with radial (β = − 0.299) and longitudinal (β = − 0.347) PS in T2DM with FMR. Conclusion FMR may aggravate the deterioration of LV stiffness in T2DM patients, resulting in decline of LV strain and function. The regurgitation degree and months with diabetes were independently correlated with LV global PS in T2DM with FMR.

Strain Rate Evaluation of Some Typical Nuclear Power Plant Components During Plant Operation

2010 ◽  
Author(s):  
Koji Dozaki ◽  
Hiromasa Chitose ◽  
Hiroshi Ogawa ◽  
Hideo Machida
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Strain History ◽  
Strain Rates ◽  
Peak Strain ◽  
Plant Operation ◽  
Thermal Transients ◽  
Reactor Water ◽  
Rate Evaluation ◽  
Reactor Internals

The dynamic aspects of loading conditions for reactor internals, piping and the like, are thought to play important roles in the initiation of failures due, for example, to stress corrosion cracking (SCC) and fatigue. Some reports show that a strain rate on the order of 10−7 s−1 most affects susceptibility to SCC in the BWR reactor water environment. Environmental fatigue, which exhibits a shorter fatigue life in reactor water than that in air, is considered to have a remarkable correlation with strain rate and its affect on fatigue life. Despite its significant affect on SCC and fatigue, the actual strain rate of components is not known and practical evaluation methods have not been developed; consequently, such failure modes as SCC and fatigue are not evaluated in design. For this paper, strain rates induced by dynamic loading during such operations as plant start-up were calculated at typical points, such as reactor internals, piping and so on. The finite element method was applied to calculate the strain history of each point, and the strain rate was evaluated. The strain rate evaluation results clearly demonstrated that thermal transients provide greater peak strain rate values than pressure transients. Strain rates on the order of 10−7 s−1 were obtained for most points of major components during such thermal transients as plant start-ups. The major factors determining the strain rate magnitude were discussed, based on the calculation results. It was shown that the rate of temperature rise was the most important parameter, because it exhibited much larger sensitivity than the other parameters on the strain rate and could be controlled by plant operation procedures. In addition, a simple strain rate evaluation method based on Green’s function was developed for a specific point with a given design condition.

A Simple Constitutive Model for Prediction of Single-Peak Flow Curves Under Hot Working Conditions

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Roxana Baktash ◽  
Hamed Mirzadeh
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Peak Flow ◽  
Rate Sensitivity ◽  
Peak Strain ◽  
Flow Curves ◽  
Hollomon Parameter ◽  
Proposed Model ◽  
Stress Coefficient ◽  
Hollomon Equation

The hot flow stress of a typical stainless steel was modeled by the Hollomon equation, a modified form of the Hollomon equation, and another modified form based on the Fields–Backofen equation. The coupled effect of the deformation temperature and strain rate was also taken into account in the proposed formulae by consideration of the Zener–Hollomon parameter or dependency of the constants on temperature. The modified Fields–Backofen equation was found to be appropriate for prediction of flow stress, in which the incorporation of peak strain and consideration of temperature dependencies of the strain rate sensitivity and the stress coefficient were found to be beneficial. Moreover, the simplicity of the proposed model justifies its applicability for expressing hot flow stress characterizing dynamic recrystallization (DRX).

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