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1.
A small instrument is described which is operated on the stage of a light microscope to trim resin-embedded specimens to precise levels for subsequent ultramicrotomy and to cut thin pilot sections for light microscopy. The operating procedure and examples of results are given. 相似文献
2.
B. P. PEHRSON J. D. LANDES 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(2):73-86
The purpose of this study is to examine the current standard fracture toughness test procedure to determine if there could be an easier method to get a JIc value from the test record. The current method for determining JIc involves a detailed computational and construction procedure. The objective in this study is to simplify the analysis for the determination of JIc. The results of this study show that the load and displacement record for a fracture toughness test can be used to directly estimate a JQ value, a provisional value for fracture toughness, JIc. The J value taken at the maximum load point can be used along with an adjustment factor to estimate a JQ value. This JQ estimate is close to the one obtained from the construction procedure of ASTM Standard E 1820. When a unit‐sized specimen is tested, that is, a specimen with a width of 50 mm and a thickness of 25 mm the maximum load point provides a direct estimate of JQ. Other sizes require a size adjustment factor, which is simply a square root relationship between the width of the test specimen and a unit width. The proposed new method of estimating JQ is simple in concept and requires a minimum number of calculations. It appears to produce values of JQ which are comparable to those obtained from the ASTM E1820 construction procedure and may produce less scatter. 相似文献
3.
提出了一种用双边带深侧槽的小尺寸圆形紧凑拉伸试样评定核压力容器(RPV)钢断裂韧性的单试作试验方法,给出了用该方法测定的两个厂家生产的核压力容器用A508CL3钢的断裂韧性参数,还与Charpy试样的试验结果及大尺寸标准试样的试验结果进行了比较。研究结果表明:用双边带深侧槽的小尺寸R-CT试样测得的断裂韧性值比相同恻槽深度预制疲劳裂纹Charpy试样的测试值更接近有效断裂韧性值,所以,用于核压力容器断裂韧性的监测是可行的。 相似文献
4.
本文研究在13SiMnNiCrMoV 结构钢中用尖裂纹的应力强度因子来反映三点弯曲缺口试样的疲劳裂纹萌生规律。当 R=0.1,f=100Hz,试样尺寸 B×W×L=12.5×25×117mm 时,缺口名义应力幅的门槛值为Δσ_(th)=3315ρ~(0.352) MPa,0.5mm≤ρ≤5mmΔK_(th)=250ρ~(0.352) MPam~(1/2)门槛值与ρ有关。同时得到缺口裂纹萌生的循环次数 N_i 与名义应力幅Δσ、缺口曲率半径ρ的定量关系是N_i=3.98×10~(22)ρ~(1.62)/Δσ~(4.85),N_i≤10~(5.5)并讨论了(ΔK_1/ρ~(1/2))_(th)与ρ无关的结论。 相似文献
5.
An isotropic model for creep damage of concrete under uniaxial compression is proposed, where the combined effect of nonlinear viscous strain evolution and crack nucleation and propagation at high stress levels is considered. Strain splitting assumption is used for creep and damage contributions. Creep is modeled by a modified version of solidification theory. As usual in the modeling of damage of concrete, a damage index based on positive strains is introduced. As particular cases, the proposed model reduces to linear viscoelasticity for long time low stress levels whereas, for very high stresses, tertiary creep causing failure at a finite time can be described. The effect of strength variation with time is also included. The model is numerically implemented to perform time integration of nonlinear equations by means of a modified version of exponential algorithm. The model is validated through comparison with experimental results. Some numerical examples are also presented, where the roles of concrete ageing and strength variation with time are investigated. 相似文献
6.
7.
Prediction of cracking within early-age concrete due to thermal, drying and creep behavior 总被引:2,自引:0,他引:2
To predict potential early-age cracking after concrete placing, a numerical simulation procedure has been completed based on a micromechanical model and empirical formulas on the property development of young concrete. The numerical model could account for the effects of hydration, moisture transport and creep. Environmental influences, such as removal of formworks, curing conditions and variations of surrounding temperature and relative humidity, have been investigated. In calculating stress field with age caused by these synthetic physical-mechanical processes, three-dimensional finite element and finite difference (3D-FE-FD) methods are combined together. 相似文献
8.
N. I. Bobyr’ A. P. Grabovskii A. V. Timoshenko A. P. Khalimon 《Strength of Materials》2006,38(1):92-98
Within framework of the continual fracture mechanics, we describe the engineering approach to the assessment of scattered
microdamage accumulation kinetics in metallic materials under elastoplastic loading conditions in case of plane stressed state.
Automatized experimental stand and the respective investigation technique are discussed. The stand has been developed based
on modification of the UMé-10T electromechanic test machine. State-of-the-art computer technologies and microprocessing hardware
are incorporated in the stand automation. We present the technique of experimental assessment of damage accumulation kinetics
in metallic structural materials under complex elastoplastic loading conditions with account of two different fracture (cleavage
and shear) processes, which technique is based on measuring the specific electric resistance of the specimen.
__________
Translated from Problemy Prochnosti, No. 1, pp. 128–137, January–February, 2006. 相似文献
9.
Hydrogen attack (HA) is the development of grain-boundary porosity by cavities filled with high-pressure methane that originates from the reaction of carbides with hydrogen at high temperatures. The cavities grow by grain-boundary diffusion and by creep of the adjacent grain material till they coalesce with neighbouring cavities to form a microcrack. Earlier work on HA has focussed on unit cells containing a single cavity, using average cavitation properties. Here, non-uniform cavitation properties on the grain-size scale are assumed in a polycrystalline aggregate, and unit cell analyses are performed to investigate the influence of the adjacent grains on the development of the grain-boundary HA. The numerical results are explained in terms of two simplified models which highlight the key parameters governing the grain deformation-grain boundary cavitation interaction process. 相似文献
10.