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金属材料疲劳行为的应力场强法描述 总被引:13,自引:0,他引:13
基于近年来发展的应力场地对金属材料的多种疲劳行为作了系统的描述,给出了缺口疲劳系Kf,疲劳尺寸系数ε,疲劳加载方式因子CL,多轴疲劳极限方程,缺口件S-N曲线的预测等多方面的定量描述,并引用了大量的实验数据加以验证,由此表明应场强法是一种很好的抗疲劳设计方法。 相似文献
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以多孔介质为研究对象,采用整场求解法分析了多孔介质温度场和流场随Ra数的变化.研究结果表明:随着Ra增加,由开始流线均匀分布为一个顺时针大窝,逐渐变化为一个顺时针大窝,一个逆时针小窝;流线出现分叉现象;流线分布在两个窝中间和外侧,即流场在小窝中间剧烈流动而在大窝中央基本上保持静止状态;当Ra很小时,热的传输主要依靠传导作用,随着Ra数逐渐增大,对流作用成为热传输的主要动力;当Ra数小于105时,高温壁面Nu数基本在-110~-17间变化,最大值发生在底部,最大值为17,最小值发生在上部,最小值为-110. 相似文献
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多孔介质中热对流的分叉机理研究 总被引:3,自引:1,他引:3
本文利用解析分析方法研究了数值模拟发现的多孔介质层中出现的对流分叉机理,指出控制方程中的Rayleigh数,是决定流动的特征参数。当Rayleigh数小于临界数值时,多孔介质内流动处于静止传热状态,并且这种状态是稳定的。如果Rayleigh数大于临界数值,非线性方程出现分叉解,文中指出,存在多个使平凡解失稳而分叉的临界Rayleigh数,当Rayleigh数由小到大经历这些临界数值时,其由平凡解发展起来的分叉解的流态,依次由单回流区转变为双回流区及三回流区。理论分析给出了分叉解和分叉解的振幅方程,阐明了分叉的机理,其结论和数值结果定性一致. 相似文献
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金属材料脆性断裂机理的实验研究 总被引:1,自引:0,他引:1
材料的脆性断裂有许多准则和模型,但对脆断机理和变化规律缺乏合理的描述,给工程应用带来不便。本文对典型脆性材料球墨铸铁、灰铸铁分别进行了拉扭双轴断裂实验和常规拉伸、扭转破坏实验;对韧性金属材料合金钢进行了单轴拉伸颈缩破坏实验。通过上述实验分析了脆性材料和韧性材料发生脆性断裂的机理特征并选择应力三维度作为应力状态参数描述危险点的应力状态,同时考察了脆性材料和韧性材料发生脆性断裂的主导因素。结果表明:韧性材料45#钢和14CrNiMoV合金钢在颈缩断面心部应力三维度值较大时发生脆性拉断,而在颈缩断面边缘处应力三维度值较小时发生剪断;脆性材料球墨铸铁在应力三维度值为0.0~0.33之间变化时均发生脆性断裂;灰铸铁在应力三维度值大于0.0时发生脆性拉断,而在应力三维度值小于0.0时发生剪断。因此可以认为,材料的细观组织结构和危险点应力状态是影响断裂机理及变化规律的主要因素。对于同种材料,随着应力三维度代数值从小向大变化材料的断裂机制由塑性剪切断裂逐渐转变为脆性断裂。本文通过对几种材料的脆性断裂危险点和断裂方向的研究给出了脆断宏观破坏条件。 相似文献
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一类多孔固体的等效偶应力动力学梁模型 总被引:1,自引:0,他引:1
一维多孔固体结构可采用等效连续介质梁模型来研究其动力学行为. 当类梁结构的高度尺寸和多孔固体单胞结构尺寸相近时,等效模型的力学行为会产生尺寸效应现象. 等效经典模型由于不包含尺度参数而无法描述尺寸相关特点,而广义连续介质力学模型则可以准确地考虑尺寸效应的影响. 基于偶应力理论,对一类单胞含有圆形孔洞的周期性多孔固体类梁结构,给出了分析其横向自由振动的等效连续介质铁木辛柯梁模型. 通过对单胞分析,在应变能等价和几何平均的意义下,定义了等效偶应力介质的材料常数. 利用已有的材料常数,推导了等效铁木辛柯梁的动力学微分方程. 将实际多孔固体结构进行完全的动力学有限元离散计算,所获得的解作为精确解以检验等效梁模型所获得的频率和振型的精度. 振型的比较借助于模态置信准则矩阵方法. 大量算例表明,等效偶应力铁木辛柯梁模型在频率和振型两方面均具有较高的计算精度. 重点研究了单胞孔径的相对大小、类梁结构高度与单胞尺寸比以及类梁结构长高比对等效梁模型精度的影响. 在此基础上,偏保守地建议了多孔固体类梁结构自振分析方法. 相似文献
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As ultra-thin films or small-scale structures become widely used in electronics and biology, knowledge concerning their near-surface mechanical properties of the materials is increasingly important. Atomic force microscopy (AFM) is employed to determine near-surface elastic modulus via force-penetration curves acquired during indentation. Samples include polydimethylsiloxane (PDMS), parylene, mica, and single-crystal silicon, and indentations are performed with single-crystal silicon and silicon nitride AFM tips. An analysis algorithm based on the secant modulus method is proposed to extract the true penetration curves from the experimental displacement curves. The penetration data is then analyzed in terms of Hertzian model to estimate the elastic modulus. Three concerns in applying nanoscale AFM indentation to the measurement of the elastic modulus of an ultra-thin material are addressed. First, the effect of the lateral force caused by the inclined angle of the cantilevered probe is investigated theoretically and by numerical simulation. A second concern is local plastic deformation induced by a sharp probe tip. In this case, numerical results show a relatively small effect on the force-penetration curves if the plastic deformation is limited to the central area below the probe tip. The deviation of the elastic-plastic simulation from the elastic estimation depends on the yield strength of the material. Finally, the effect of stiffness matching between the AFM probe and the sample is a key issue that is studied numerically, and appropriate stiffness matching criteria are suggested. 相似文献
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A. Rathkjen 《Journal of Elasticity》1997,47(2):167-178
A state of plane stress is illustrated by means of two families of curves, each family representing constant values of a derivative
of Airy's stress function. The two families of curves form a map giving in the first place an overall picture of regions of
high and low stress, and in the second place, the map comprises a complete graphic representation of the stress at any point.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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S.-W. Jeon K.-W. Lee J. Y. Kim W. J. Kim C.-P. Park D. Kwon 《Experimental Mechanics》2017,57(7):1013-1025
We propose a generalized approach based on fracture mechanics and contact mechanics to estimate the fracture toughness in metallic materials from instrumented indentation testing. Models were developed for brittle and ductile fracture. Different criteria were applied to each model to determine the critical fracture point during indentation. For brittle fracture, the critical fracture point was defined in terms of the critical mean pressure; for ductile fracture, the critical fracture point was derived from fracture strain and critical plastic zone size. Each fracture criterion was used to determine the indentation fracture energy corresponding to the fracture energy required for crack extension. The fracture toughness was estimated for various metallic materials using each model and compared with standard fracture toughness tests. 相似文献
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细胞与胞外基质微环境的物理力学相互作用涉及许多复杂的生物信号转导通路,对于细胞的增殖、分化、收缩、迁移和凋亡等都起着重要的调控作用。在单细胞水平上,运用细胞牵引力显微镜方法定量研究细胞活动规律及特点具有重要的生理病理学意义。牵引力显微镜方法的核心在于如何通过基底变形信息反演得到细胞牵引力场。本文首先介绍细胞牵引力反演方法的基本原理,然后针对细胞牵引力求解过程中所涉及到的反问题的病态本性,重点介绍近十几年来细胞牵引力反演算法的研究进展(包括边界元反演算法、基于集中力假设的反演算法、基于积分Boussinesq解的反演算法、基于傅立叶变换的反演算法、基于最优滤波的反演算法等)。 相似文献
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Some applied problems of the mechanics of strain-hardening processes in metallic materials are considered. To solve these
problems, the concept of loading surface, which separates the elastic and elastoplastic domains in the stress space, is used.
Strain-hardening models are analyzed. For a wide range of steels and alloys, the most commonly used hypothesis of isotropic-and-kinematic
hardening is experimentally justified
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Translated from Prikladnaya Mekhanika, Vol. 41, No. 10, pp. 12–51, October 2005. 相似文献
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根据电磁学原理,提出了基于电能耗散的疲劳损伤定义,指出其较能反映金属材料疲劳损伤的特征。获得了用电阻变化测量疲劳损伤的公式,应用计及疲劳极限和循环应力幅影响的非线性累积疲劳损伤模型,给出了金属材料疲劳损伤的剩余寿命预测公式。通过正火45^#碳钢的旋转弯曲疲劳试验,验证了本文提出的剩余寿命预测公式的可靠性,和韧性耗散测量疲劳损伤相比较;说明了用电阻测量疲劳损伤的合理性。 相似文献
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