Papers by Keyword: Rate Effect

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Authors: Lu Ming Shen, Zhen Chen
Abstract: To better understand the responses of ultrananocrystalline diamond (UNCD) under extreme working conditions, a numerical study is performed to investigate the size, loading rate and thermal effects on the material properties of UNCD films. A combined kinetic Monte Carlo (KMC) and molecular dynamics (MD) method is first applied to simulate the growth of polycrystalline UNCD films. The responses of the resulting UNCD films with various grain sizes are then investigated by applying displacement–controlled tensile loading with different rates and temperatures in the MD simulations. The preliminary results presented in this paper provide a better understanding of the combined size, rate and thermal effects on the material properties of UNCD.
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Authors: J. Weerheijm
Abstract: The rate effect on concrete tensile strength can be modeled by the description of crack extension in a fictitious fracture plane [1,2].The plane represents the initial, internal damage and the geometry of the final fracture plane. In the paper, the same approach is applied to model the failure envelope for the biaxial loading condition of static lateral compression and axial impact tensile load. The predicted failure envelope is compared with data from experimental work.
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Authors: Ping Zhang, Ning Li, Ruo Lan He
Abstract: More and more engineering practice indicates rock mass is prone to lose its stability through crack coalescence under dynamic loading, such as blasting and earthquake. However, the crack coalescence pattern of rock specimens containing two or more flaws has not been studied comprehensively under dynamic loading. In this paper, the mechanism of the crack coalescence and peak strength of sandstone-like materials containing two parallel flaws are studied under uniaxial static and dynamic loading with strain rates 1.7×10-5 s-1 and 1.7×10-1 s-1. Through the comparisons of the propagation length, coalescence pattern of the cracks and strength increase of the pre-cracked specimens under static and dynamic loading, the dynamic response of the crack coalescence is found different from static loading under different geometric setting of the flaws. The inertia effect of the crack propagation is revealed under dynamic loading, that is to say, the growth of the secondary cracks tends to the original propagation direction, and the direct and immediate coalescence is taken place easily between two pre-existing flaws, which is different from the kinking coalescence under static loading. So, the inertia effect of the crack propagation is regarded as the main cause of the strength increase of the brittle material under dynamic loading for medium strain rates. In virtue of the explanation, another cause of the mode II shear fracture occurred under earthquake is opened out.
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Authors: Bo Han, Yu Tao Ju, Chang Sheng Zhou
Abstract: The fracture toughness of HTPB propellant has a significant rate effect. In order to establish a fracture criterion considering rate effect for HTPB propellant, experiments were conducted at different loading rates. Two kinds of specimens were used to get the fracture properties. Stress intensity factor and J-integral were obtained by the single edge notched tension specimen test. A power law cohesive zone model was obtained by the experiment based inverse method. Through comparing we found that the stress intensity factor and J-integral cannot model the rate effect in fracture process. The cohesive zone model (CZM) has a constant critical separation distance at different loading rates and has a capability to model the rate effect during the crack initiation and propagation process. A finite element simulation in ABAQUS was given to demonstrate its capability to model the crack propagation.
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Authors: Robert L. Browning, Hung Jue Sue, Kousuke Ohtani, Yasuhito Ijichi, Yuki Iseki
Abstract: The scratch behavior of a set of model soft thermoplastic olefin systems containing at least 65 wt% of ethylene-propylene rubber (EPR) in polypropylene was analyzed using a standardized progressive load scratch test. It was found that raising the ethylene content in the EPR introduces crystalline phases, as evidenced by differential scanning calorimetry, and significantly alters the scratch behavior. A strong effect was also observed by changing the rate at which the scratch test was applied. This paper will discuss these effects based on the scratch damage mechanisms observed.
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Authors: Azranasmarazizi Ayob, Nor Azizi Yusoff, I. Bakar, Nur Abidah Azhar, Ameer Nazrin Abd Aziz
Abstract: A wide range of industrial applications, on land and offshore, require the solution of time domain problems and an associated understanding of rate effects in clay soils. In recent decades many researchers have examined the correlation between shear strength of soils and variation of shear strain rate and it is generally accepted that the strength increases by 1-5% for each order of magnitude increase in shear strain rate. This paper discusses the effects of penetration rate on the penetration resistance (qc) by using cone penetration test (CPT) test setup. The research had been conducted at RECESS and cone penetration test were used in three selected range of rate which were 0.5 cm/s, 1cm/s and 5cm/s. In addition, Mackintosh probe testhad been considered as comparison with CPT test for the unconfined compressive strength. The result shows different penetration rate influenced the soil shear strength. For the slowest rate (0.5 cm/s), the shear strength was approximately 0.15% less compared to the standard rate (2 cm/s). However, for the highest rate (5 cm/s), the shear strength was 0.22% more than the reference rate (0.5 cm/s). In conclusion, it is suggested that the RECESS clay soil influenced by the rate effect and in agreement with previous research findings.
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