Anomalous temperature dependence and tension–compression asymmetry of Fe3Al intermetallics—an internal variable approach

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.     

焊接缺陷评定参量的统计规律研究

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。     

发展油料能源树种与开发生物柴油前景分析

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。     

含盐冻结粉质粘土单轴抗压强度试验研究

通过对饱和含盐冻结粉质粘土单轴抗压强度试验,得到了试验条件下土体的单轴抗压强度与含盐量、负温的关系;讨论了应变速率一定,温度和含盐量变化时,含盐冻结粉质粘土的屈服应力和抗压强度间的关系;提出了相对温度这一新概念,并给出抗压强度与相对温度间的线性关系。相对温度的引入建立了盐渍土和非盐渍土力学性质的关系,从而可以用非盐渍土力学性质预测盐渍土的力学性质。     

纤维类型及取向对纤维-UHPC基体拔出性能影响研究

纤维与基体之间的粘结能力和机械锚固作用是基体将荷载传递给纤维的决定因素之一,不同类型的纤维和取向在拉拔时的受力形式和破坏形式决定试件承载能力。采用单根纤维拉拔试验探究了纤维类型、取向对超高性能混凝土(UHPC)界面拉伸性能的影响。结果表明:随着纤维取向的增加拔出荷载先增大后减小,在45°时拔出荷载达到最大值;随着纤维取向增加,纤维拔出时对基体破坏面积增大,纤维拔出时对于基体的破坏能力:波纹线>端勾型>直线型。由第一峰值荷载分析,波纹型钢纤维相比于直线型和端勾型钢纤维更容易脱黏。对纤维拔出时进行力学行为分析,波纹型钢纤维和端勾型钢纤维拔出过程中首先发生纤维屈服,随着荷载持续基体产生破坏,直线型钢纤维在拔出过程中最先发生纤维与基体脱黏。     

不同弛豫时间下低合金高强度钢的组织和拉伸性能

研究了低合金高强度钢在不同弛豫时间下的组织和拉伸性能。结果表明：在适当的弛豫时间下。能进一步提高材料的屈服强度和抗拉强度。     

Viscoelasticity and shear yielding onset in amorphous glassy polymers

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.     

Representation of Crack-Tip Plasticity in Pressure Sensitive Geomaterials: Large Scale Yielding

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.     

统计技术在热轧钢板生产过程中的应用

介绍了应用于统计诊断和统计控制的原理，用此原理对热轧钢板屈服强度进行分析，提出了稳定控制板材性能的措施。