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51.
The effect of specimen thickness on the experimental and finite element characterization of CTOD in extra deep drawn steel sheets 总被引:1,自引:0,他引:1
Recent experimental results by us have indicated that the load-drop technique can serve as a valid fracture criterion for
predicting elastic-plastic fracture in extra deep drawn (EDD) steel sheets or in predominantly plane stress conditions. The
purpose of this investigation is to examine the validity of aJ-integral as a fracture parameter and theJ-CTOD relation for the determination of critical CTOD in predominantly plane stress fracture (CTOD-crack tip opening displacement).
Fracture tests were performed and experimental results were generated on fracture behaviour of EDD (0·06%C) steel sheets with
CT specimens and using ‘load-drop’ as a fracture criterion. Critical CTOD was determined by using theJ-CTOD relation in addition to several existing techniques. A full 3-D finite element model was formulated to verify the critical
load, critical CTOD and plastic-zone size. The critical CTOD was shown to increase with increasing specimen thickness and
appeared to be approaching a higher limiting value. The characteristic features of predominantly plane stress fracture or
general yielding fracture mechanics are summarized in conclusion 相似文献
52.
Wonkyu Bang Hyun Tae Lim Tae Kwon Ha Young Won Chang 《International Journal of Mechanical Sciences》2003,45(10):1661-1670
Tension/compression asymmetry in the high-temperature flow and anomalous yield/flow stress of Fe–28 at% Al–5 at% Cr alloy has been investigated. Flow curves were obtained from a series of tensile and compressive load relaxation tests. Constitutive relations at each deformation conditions were formulated using the internal variable theory based on dislocation dynamics. In this study, high-temperature flow stress of selected material was to be safely described as the sum of internal stress and frictional stress. The anomaly and peak temperature of yield strength seem to be controlled by the anomaly of internal stress and the relative portion of internal and frictional stress in total flow stress, respectively. Asymmetric flow stress was observed in analogy with yield strength. In terms of constitutive parameters, critical stress for frictional flow (Σ0) exhibited considerably higher value in compression, which physically postulates increased critical resolved shear stress (CRSS). Considering the crystallography and microstructure, it is presumably due to the ‘extrinsic’ effect of non-deviatoric stress tensor, as proposed in other studies. 相似文献
53.
为了应用概率断裂力学方法对焊接构件进行安全评定,本研究主要揭示缺陷评定参(?)的统计规律性。用随机抽取的J506、J507焊条焊接16Mn钢板,然后制备接头焊缝中心具有裂纹的宽板试件。通过拉伸试验、依据全面屈服准则确定接头焊缝金属的临界裂纹尺寸2α_(cr);经过统计计算,发现影响2α_(cr)的最显著因子,获得了2α_(cr)服从的最优统计分布。 相似文献
54.
发展油料能源树种与开发生物柴油前景分析 总被引:6,自引:0,他引:6
种植油料能源树种,开发生物柴油对加快中国荒山绿化、保护环境、为农民增收和替代部分化石燃料具有十分重要的战略意义。全国现有油料能源树种资源约300万ha.,年可收获果实90多万t,能加工生物柴油30万t。还有5400万ha.宜林荒山荒沙地和1亿ha.边缘性难利用土地可以种植3600万ha.油料能源树种,建设“绿色油田”和开发生物柴油,其潜力巨大。 相似文献
55.
高强让压锚杆支护效果数值模拟研究 总被引:5,自引:0,他引:5
高强让压锚杆支护就是在高强锚杆托盘和螺母之间加一让压环,通过让压环在一定压力下的变形使围岩卸压,可有效地控制住复杂难支护巷道的大变形.采用大型三维岩土工程数值模拟软件FLAC3D,对高强让压锚杆支护前后围岩变形破坏规律进行了数值模拟,对高强让压锚杆支护前后围岩的应力、位移及锚杆轴力的变化情况等进行了系统分析.结果表明,高强让压锚杆支护显著改善了巷道支护效果,有效地控制了复杂困难巷道的损伤变形. 相似文献
56.
57.
58.
In the present work, the effect of viscoelasticity on the yield behaviour of a polycarbonate, PC, was studied and the identification
of a yield criterion which takes into account the effects of the mechanical history on the onset of plastic strain, was attempted.
The attention was focused on the shear yielding plastic deformation process and different loading histories were performed
under uniaxial compression: constant strain rate at different rates, stress relaxation at different applied strain levels,
creep under different stress levels. Some tests were also carried out under shear loading, in which the hydrostatic stress
component is equal to zero and its effect on the yield onset can be considered. For the definition of a yield criterion, different
quantities, some already proposed in an analogous work on a styrene-acrylonitrile copolymer (SAN), were considered and determined
at yield onset for each of the applied loading histories. The results obtained in this work show that the relative ratios
of the viscoelastic strain over the overall strain and of viscoelastic energy over the deformation work are fairly constant
irrespective of both loading history and stress state. The re-elaboration of the data previously obtained on SAN is consistent
with these results.
Discussing the experimental data, differences between the mechanical behaviour of the two glassy polymers were pointed out
and a more difficult activation of the plastic deformation process of PC than SAN was generally observed. 相似文献
59.
We model large scale Mohr-Coulomb yielding that accompany fractures in weak rocks, by means of dislocations. The basic equations
are derived from a simple model of the crack tip plasticity which represents the plasticity by superdislocations placed at
the effective centres of the crack tip process zone. 相似文献
60.