共查询到20条相似文献,搜索用时 15 毫秒
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Experimental Mechanics - Recently, a technique for rapidly determining a material’s fatigue limit by measuring energy dissipation using infrared thermography has received increasing interest.... 相似文献
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G. V. Galatenko 《International Applied Mechanics》2003,39(1):105-109
The constrained plastic deformation at the front of a circular mode I crack under nonaxisymmetric loading in the crack plane is studied. It is shown that the normal stresses in the plastic zone depend on the polar angle and external stresses. The constraint is maximum at those points on the crack front along tangents to which the maximum external tensile stresses act 相似文献
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塑性应变能使材料微观组织结构发生不可逆变化,从而引起等效宏观应力,该应力随循环加载而增大.假定材料疲劳源处破坏是由最大拉应力引起的,最大等效宏观应力与外加应力叠加达到材料本征断裂应力时形成微裂纹.微裂纹引起上述两部分应力变化,继续加载直至宏观裂纹出现,从而得到材料的疲劳寿命.本文所建立的多轴疲劳寿命公式包含材料参数、拉应力以及塑性应变能等,以上数据可通过单轴疲劳数据和有限元方法获得.通过对SM45C材料的计算验证,表明该模型对多轴随机应变加载低周疲劳寿命,具有良好的预测结果. 相似文献
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O. E. Scott-Emuakpor T. J. George C. J. Cross M.-H. H. Shen 《Experimental Mechanics》2011,51(8):1317-1323
The dissipation of strain energy density per cycle was analyzed to understand its trend through a fatigue process. The motivation
behind this analysis is to improve a fatigue life prediction method, which is based on a strain energy and failure correlation.
The correlation states that the same amount of strain energy is dissipated during both monotonic fracture and cyclic fatigue.
This means the summation of strain energy density per cycle is equal to the total strain energy density dissipated monotonically.
In order to validate this understanding, the strain energy density per cycle was analyzed at several alternating stress levels
for fatigue life of Aluminum 6061-T6 (Al 6061-T6) between 103 and 105 cycles. The analysis includes the following: Alternating between high and low operating frequencies (50x magnitude difference),
interruption of cyclic load during testing, and idle/zero-loading intervals of 20–40 minutes in-between cyclic loading sequences.
All experimental results show a consistent trend of cyclic softening as the loading cycles approach failure; however, due
to an inefficient curve fit procedure of the stress-dependent strain equation at low alternating stresses onto the experimental
stress-strain data, a new approach for calculating the strain energy density per cycle is explored and shows promising results. 相似文献
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A novel experimental rig capable of generating a versatile dynamic loading has been designed and tested to overcome the shortcomings of conventional fatigue testing machines such as the difficulty in providing zero crossing aperiodic loading. The main principle of this new design is based on two, single degree of freedom based excited oscillators, where inertial forces act on a specially designed specimen. By changing the natural frequency of the oscillator, the extent of the preloads and pattern of the excitation signal on the shaker, the rig provides a new and robust means of fatigue testing, particularly for aperiodic loading. 相似文献
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以拉扭簿壁管试件为研究对象,根据多轴临界面上的应力应变特性及多轴疲劳临界面法的结果,结合单轴循环应力应变关系,研究了多轴比例与非比例加载下的循环应力应变关系,推导出多应力应变关系模型,经拉扭复合比例与非比例物载试验难证,其预测结果与实测值相符合。 相似文献
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本文首先引入岩石塑性应变梯度理论,地下隧道受开挖的影响,岩石的原岩应力重新分布,靠近隧道岩石变形局部化,往往出现塑性变形区,作者进一步论证了,靠近隧道岩石在建立地下震动作用下的数学力学模型时须考虑塑性应变梯度,进而从地下隧道弹塑性区内抽象出一个单元体,这个单元体在地震横波作用下受力状态必须是纯剪应力状态,并假设岩石的力学本构关系为双线性,建立了单元体在地震横波作用下受力状态必然是纯剪应力状态,并假设岩石的力学本构关系为双线性,建立了单元体数学力学模型,推导出软化区的宽度为α(α=2πl),基于上述,最后解决了地下隧道失稳破坏的力学机理。 相似文献
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为分析岩石塑性变形与损伤的关系,在定义岩石的初始损伤和临界损伤,提出塑性体积应变分析方法,从而以塑性体积应变为损伤变量,采用归一化方法建立岩石的损伤本构模型。采用递增循环加载实验确定岩石损伤本构模型中的弹性卸载模量和弹性应变比例系数两个参数。通过实验和理论分析得出:当荷载较小时,普通单轴压缩状态下岩石损伤随荷载的增加具有减小趋势,荷载超过一定数值后,岩石损伤才开始增加;单轴递增循环压缩状态下当循环荷载大于约35%峰值强度后,卸载后岩石的损伤具有增加的趋势,小于该荷载之前具有减小的趋势。整个加载过程的理论应力-应变曲线能很好地与实验结果相吻合,在循环加载区间理论结果还能体现出岩石实验结果中的回滞环。 相似文献
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The rigid-plastic assumption has greatly simplified the theoretical analysis of dynamic plastic response of structures.Within this framework,a common tool is th... 相似文献
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基于微观织构演化,本文对镁合金的宏观塑性本构模型进行了改进,得到了室温下镁合金AZ31B和AZ61A单轴循环拉压载荷作用下的应力应变曲线。模型中区分了滑移、孪晶与去孪三种不同微观塑性变形机制,并且研究了它们对材料宏观循环塑性行为的影响。通过引入初始非零背应力来模拟循环应力应变曲线中拉压不对称性,给出了材料在单轴循环拉压载荷下背应力及屈服面的演化规律,并运用线性预测塑性回拉技术与隐式积分法求解相应的非线性方程组,编写了与.ABAQUS接口的UMAT用户子程序。预测与实验结果的比较显示该模型能较好地模拟镁合金材料在单轴循环拉压载荷作用下的力学行为,具有较高的准确性与良好的实用性。 相似文献
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By choosing the dissipation energy as the damage variable,corresponding damage evolution equations are established,respectively,for the mechanical cyclic loadin... 相似文献
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Transport in Porous Media - We propose a process-based method for constructing a pore network model of granular packings under large deformations. The method uses the radical Voronoi tessellation... 相似文献
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岩体原位流变荷载试验的力学参数与模型反演 总被引:4,自引:0,他引:4
根据现场岩体原位测试的60m和70m处两试验点的流变变形曲线,首先通过曲线特征筛选出了能够描述其变形特性的流变模型(三参量固体模型,Burgers模型),基于粘弹性分析理论及两步反分析法思路,建立了荷载试验的三参量固体模型、Burgers模型的位移优化反演格式,利用分级加载所获得的瞬时弹性位移,反算出了两试验点处的岩体弹性体积模量K、剪切模量G0和变形模量E0,并由优化反演方法获得了两模型的所有流变参数G1,η1,η2和E1以及长期弹性模量E∞。利用所获得的粘弹性参数分别计算出了在不同载荷下两种模型的理论解析曲线,并与实测曲线进行了分析对比,最终获得了能够较真实地描述试验区域岩体流变变形特性的最佳模型,即三参量固体模型。通过对比分析验证了所用思路及方法的正确性和实用性,文中方法虽然应用于流变荷载实验情况,但其具有一定的普遍意义,可应用于不同状况的流变实验的参数确定和模型反演。 相似文献
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A. M. Avdeenko 《Journal of Applied Mechanics and Technical Physics》2000,41(6):1070-1077
A strain diagram for a locally inhomogeneous medium (a medium with a porous structure or a system with noncut particles) is constructed on the basis of the Cosserat nonlinear–pseudocontinuum model. A modified criterion of geometrical softening that allows one to establish the dependence of the moment of stability loss on the statistical characteristics of the medium is considered. 相似文献
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采用较真实的材料本构模型,在Ponter和Karadeniz提出的扩展的安定性理论以及彭得到的考虑混合强化的安定性定量的基础上,发展了计及应变强化和循环强化的结构塑性安定区的分析方法。通过将循环强化和应变强化分别引入子区域VF和VS,利用材料安定性假设,得到了较为合理的塑性安定边界,克服了以前的工作中对处于VF和VS区中材料分别采用完全各向同性强化(或假设热应力史是弹性应力史)和完全塑性的理想材料 相似文献