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81.
A modified miniaturized version of the Direct Impact Compression Test (DICT) technique is described in this paper. The method
permits determination of the rate-sensitive plastic properties of materials up to strain rate ∼105 s−1. Miniaturization of the experimental setup with specimen dimensions: diameter d
S = 2.0 mm and thickness l
S = 1.0 mm, Hopkinson bar diameter 5.2 mm, with application of a novel optical arrangement in measurement of specimen strain,
makes possible compression tests at strain rates from ∼103 s−1 to ∼105 s−1. In order to estimate the rate sensitivity of a low-alloy construction steel, quasi-static, Split Hopkinson Pressure Bar
(SHPB) and DICT tests have been performed at room temperature within the rate spectrum ranging from 5*10−4 s−1 to 5*104 s−1. Adiabatic heating and friction effects are analyzed and the final true stress versus true strain curves at different strain
rates are corrected to a constant temperature and zero friction. The results have been analyzed in the form of true stress
versus the logarithm of strain rate and they show two regions of a constant rate sensitivity : relatively low up to the strain rate threshold ∼50 s−1, and relatively high above the threshold, up to strain rate ∼4.5*104 s−1. 相似文献
82.
An experimental investigation was performed to study a specific axial crush configuration response of steel, square box components under quasi-static testing conditions. For a specific cross-sectional geometry/fabrication process, test specimens were obtained from commercially produced, welded tube lengths of ASTM A36 and ASTM A513 Type 1 plain low-carbon steels and AISI 316 and AISI 304 austenitic stainless steels. Removable grooved caps were used to constrain tube test specimen ends, and collapse initiators in the form of shallow machined grooves were used to control the initial transverse deformations of the test specimen sidewalls. The progressive plastic deformation for all of the test specimens was restricted to the prototype configuration response (fold formation process and the corresponding axial load-axial displacement curve shape) of the symmetric axial crush mode. Crush characteristics were evaluated and, for each material type, observed differences were less than 7% for maximum and minimum load magnitudes and less than 2% for energy absorption, displacement, and mean load quantities in both the initial phase and the secondary folding phase cycles. Overall, results of the study indicate that for a significant range of material strengths, a controlled and repeatable energy absorption process can be obtained for commercially produced steel box components undergoing symmetric axial crush response. 相似文献
83.
This paper deals with the evolution of inhomogeneous deformation in shape memory alloy strips and mild steel strips under uniaxial tension. New experiments on NiTi strips, which initially are in an austenitic phase, show that at a critical stress level martensite nucleates in sharp bands inclined at 55° to the axis of loading. Under prescribed end displacement martensite subsequently spreads either by steady-state propagation of inclined transition fronts or via a criss-cross pattern of finger-like features. Similar events have been reported in the literature regarding the evolution of Lüders bands in fine grained steel strips and wires. The similarity of macroscopic events, despite the different mechanisms of instability at the micro-level, prompted us to approximate the material behavior as a finitely deforming elasto-plastic solid with a trilinear up-down-up nominal stress-strain response. Two such stress-strain responses were used in finite element simulations of strip tension tests. In the first the true stress-strain response maintains its stability and in the second the intermediate branch has a negative slope. While both material models produced inhomogeneous deformations with features similar to those of the experiments, the larger initiation peak associated with the second gave results which closely resembled specific experiments. The numerical simulations confirmed that the evolution of events seen in experiments on SMAs and mild steels is strongly influenced by overall geometric (structural) effects. Furthermore, the success of this simple continuum constitutive model strongly suggests that continuum level events remain dominant players in such fine grained materials. 相似文献
84.
In order to characterise chatter marks, in this work, various ground samples are investigated by means of two different optical surface analysis techniques: by using a confocal white light microscope and an angle-resolved light scattering sensor, respectively. The latter is also applied to an industrial belt grinding process in both roughness- and waviness-modes of measuring. These in-process measurements are found in good agreement with those of visual counting. Data processing in terms of the Fourier transformation it is shown to equally well accesses the wavelength of chatter marks in both roughness- and waviness-modes. Therefore it is concluded that chatter marks occurring during the industrial belt grinding can be seen as a superposition of roughness changes and waviness. 相似文献
85.
介绍了铁基线材、高铬铸铁、高锰钢等3种钢铁的光电光谱定量测定方法。该方法是通过选用与分析材质同基体,主成分接近的标准样品绘制校准曲线,采用自编的计算机校正程序,找出试样的光谱分析值和化学分析值之间的关系模型,并将模型通过计算机程序拟合到控制样品中,当进行材质测定时,只需要在日常标准化操作后将拟合好的控制样品对校准曲线进行控样校正,就可以直接进行试样的测定。该测定方法实用,结果可靠,适用于无相同标准样品条件下的试样光谱定量分析。 相似文献
86.
87.
88.
The ferrite/pearlite banded structure causes the anisotropic behavior of steel. In this paper, digital image correlation (DIC) was used to analyze the micro deformation of this microstructure under uniaxial tension. The reliability of DIC for this application was verified by a zero-deformation experiment. The results show that the performance of DIC can satisfy the requirements of the tensile deformation measurement. Then, two uniaxial tensile tests in different directions (longitudinal direction and transverse direction) were carried out and DIC was used to measure the micro deformation of the ferrite/pearlite banded structure. The measured results show that the ferrite bands undergo the main deformation in the transverse tension, which results in the relatively weaker tensile properties in the transverse direction than in the longitudinal direction. This work is useful to guide the modification of the bands morphology and extend the application scope of DIC. 相似文献
89.
《印度化学会志》2023,100(1):100853
In this study, the feasibility of the complete replacement of lime by steel slag (SS) as a calcium material with deactivated ZSM-5 for the preparation of autoclaved aerated concrete (AAC) was investigated. The effects of the Ca/Si ratio on the foaming effect, bulk density and mechanical strength, mineral composition, pore structure and microstructure were studied. The results show that the increase of the Ca/Si ratio enhanced the early foaming effect. AAC with an optimum Ca/Si ratio of 0.92 had a compressive strength and bulk density of 3.1 MPa and 535 kg/m3, respectively, meeting the national standards (GB/T 11968-2020) of grade A2.5 and B05. The increase of the Ca/Si ratio significantly reduced the number of pores with a pore size greater than 60 μm. In addition, X-ray diffraction (XRD) and scanning electron microscopy (SEM) results show that an elevated Ca/Si ratio will change the shape and crystallinity of tobermorite. 相似文献
90.
Billal Zayat Debanjan Mitra Ahamed Irshad Aravamuthan Sundar Rajan Sri R Narayanan 《Current Opinion in Electrochemistry》2021
The instability of iron under anodic conditions makes iron-based electrode substrates unsuitable for alkaline electrolyzers and rechargeable alkaline batteries. Therefore, significantly more expensive substrates such as nickel foam or sintered nickel are used. Nickel adds a significant cost to electrolysis and energy storage systems. We show that iron substrates can be stabilized using a unique protective thermal coating. These coatings can also yield some of the most electrocatalytically active electrodes in addition to showing no notable change in performance even after 1500 h of anodic polarization. Besides sintered iron, low-carbon steel mesh can be stabilized similarly. Low-carbon steel protected by a thin layer of lithium-doped cobalt spinel was found to be an excellent current collector for positive nickel hydroxide electrodes in alkaline batteries. Thus, surface-modified iron substrates, 40 times less expensive than nickel, are promising for lowering the material costs of alkaline water electrolyzers and rechargeable alkaline batteries. 相似文献