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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而引起等效宏观应力,该应力随循环加载而增大。假定该应力的一种分布函数,将疲劳极限以上加载等效为塑性应变,建立了塑性应变与加载应力成线性关系的表达式,由此得到循环加载的塑性应变能。导出其最大应力与外加应力叠加达到材料本征断裂应力时的裂纹成核寿命,并由微裂纹引起上述两部分应力变化,得到继续加载直至宏观裂纹出现的疲劳寿命。所建立的多轴疲劳寿命公式由三个材料参数表达,并通过单轴疲劳试验数据确定。初步研究表明,该模型对所引用的多轴疲劳试验数据有很好的预测能力。 相似文献
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超塑拉伸变形应变速率敏感性指数的力学解析 总被引:3,自引:1,他引:2
从拉伸变形的状态方程和力学基本理论出发,导出了塑性和超塑性拉伸变形mξ、mv 和mF(mξ、mv。和F分别为恒应变ξ、恒变形速度v和恒载荷F的应变速率敏感性指数)的函数表达式,而且理论计算值与典型超塑性合金ZnA15的试验数据吻合,这便从理论上解答了“拉伸变形应变速率敏感性指数的力学涵义及其规范测量”一文从试验上提出的问题,即:为什么mξ、mv和mF随应变速率ξ的变化规律互不相同,甚至出现了mF会大于1,mv会是负值的反常结果。对这些问题的理论解答便进一步揭示了m值的力学本质。 相似文献
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在冷轧薄带钢和带钢平整时,轧件的塑性系数的准确性直接关系到控制系统的稳定性和带钢成品的质量。根据压力AGC控制系统的原理,得出了轧件塑性系数的计算公式,并将该公式与根据辊缝变化量和压力变化量之间的关系推导出的塑性系数的计算公式进行误差大小的比较,证明了由AGC参数方程得出的轧件塑性系数的计算精度较一般方法高,并经实验证实了理论分析的正确性。 相似文献
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Y. Dadgar Asl M. Sheikhi A. Pourkamali Anaraki V. Panahizadeh R. M. Hoseinpour Gollo 《The International Journal of Advanced Manufacturing Technology》2017,91(5-8):1481-1492
In this research, the fracture phenomenon was investigated on flexible roll forming process of channel section using ductile fracture criteria and forming limit diagram (FLD) by considering the effect of anisotropy. For this purpose, a finite element simulation of the process using the ABAQUS software was done. The fracture in this process was evaluated by considering six types of ductile fracture criteria by UMAT subroutine implementation on the FEM software and using FLD criterion. Experimental tests were performed on 27 blanks of Al6061-T6 using flexible roll forming machine made in Shahid Rajaee Teacher Training University (SRTTU). Numerical results were validated by experimental results. In addition, prediction of occurrence and fracture position by ductile fracture criteria and FLD criterion were compared with experimental results; the Argon criterion was chosen as the most appropriate criterion to predict the fracture position and its occurrence. The fracture occurrence was only observed in a 60° bending angle for 1.5- and 2-mm thicknesses, and the fracture position error percentages of the Argon criterion with experiments for these cases were 18.7 and 3.5%, respectively. Also, the effects of parameters such as sheet thickness, bending radius, and bending angle on the fracture phenomenon by using the selected criterion of Argon were studied. 相似文献
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Jun-Seok Choi Hyun-Chul Lee Yong-Taek Im 《Journal of Mechanical Science and Technology》2010,24(9):1885-1890
A numerical algorithm based on the element deletion method and rigid-viscoplastic finite element approach depending on Cockcroft-Latham
and specific plastic work fracture criteria was applied to predict formation and evolution of possible cracking in a cold
extrusion of aluminum and steel alloys. The Cockcroft-Latham fracture criterion induced an internal crack while an external
crack occurred owing to the specific plastic work criterion in simulations. As a result, the Cockcroft-Latham criterion was
found to be valid for predicting chevron cracking in comparison with the experimental observation available in the literature.
Using the Cockcroft-Latham criterion, cracking was carefully investigated in terms of the size of the crack and gap distance
between cracks depending on the number of elements and boundary condition at the punch interface. The critical damage values
for the Cockcroft-Latham fracture criterion were also calculated based on the tensile instability and fracture conditions
to investigate their effect on possible cracking. Finally, a processing map based on the Cockcroft-Latham fracture criterion
for preventing chevron cracking in the cold extrusion of commercially available steel alloy was developed by considering processing
parameters such as reduction in area and semicone angle. According to this investigation, the developed element deletion method
with the Cockcroft-Latham fracture criterion was reasonably accurate for carrying out chevron cracking analyses in the cold
extrusion with proper selection of a critical damage value. 相似文献
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研究了超高变形速率下材料的塑性(延性)演化规律和断裂行为。通过45钢、Ti-6Al-4V、Al2024-T3和Al2024-T351四种材料高速变形数据,考察了JC断裂准则和MSV断裂准则对于高应变率下材料失效行为的表达能力。研究发现,JC断裂准则中材料的失效应变随着应变率的增加单调增大,JC断裂准则能够描述中低应变率范围内(0-10~3/s)材料的断裂情况;对于应变率更高(≥10~4/s)情况下材料的断裂行为,JC断裂准则不能描述。材料的MSV在约10~4/s时突然增大,MSV断裂准则能够描述超高应变率下材料的断裂趋势。 相似文献
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A unified brittle fracture criterion for cracks and V-notches under mixed mode loading is proposed by extending the maximum
circumferential stress criterion and Novozhilov’s criterion. The mixed mode fracture toughness and crack orientation of PMMA
plates with a sharp V-notch are predicted by the proposed criterion. Tests were also carried out in order to investigate the
mixed mode fracture of the PMMA plates. The fracture criterion is validated by comparison to experimental results. 相似文献
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板料成形过程的宏观断裂行为依赖于其微观断裂机理,因此成形过程模拟中的断裂准则的准确选择对于断裂预测具有重要意义。以高强钢TRIP780板料为研究对象,设计从剪切到拉伸应力状态的五种断裂试验,结合宏观拉伸试验和扫描电子显微镜(Scanning electron microscope,SEM)分析研究不同应力状态下TRIP780板料的断裂机理,得到不同应力状态下正应力和切应力与断裂机理的关联关系,引入正应力与切应力的影响构建MMC断裂准则,应用于板料压剪应力区间的断裂行为预测。结果表明,反映断裂机理的MMC准则能适用于板料压剪和拉剪变形应力状态下断裂失效的准确预测。 相似文献
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The purpose of this study is to clarify the mechanics of ductile fracture in bulk metal forming processes by finite-element analysis and experiments. The author has developed a computer program, based on a conventional computer program involving the finite-element method, by which the behavior of crack propagation after ductile fracture can be analyzed. The phenomenon in which a ‘chevron crack’ appears periodically in the axial direction during drawing has been simulated using the developed computer program. Special attention is focused on the effect of various kinds of ductile fracture criteria on chevron crack formation and evolution during drawing. Results obtained are summarized as follows. First, the analytical results obtained using Gurson's fracture criterion and using Oyane's fracture criterion agree well with the experimental result. Second, the analytical results using Cockcroft and Latham's fracture criterion and using Brozzo et al.'s fracture criterion agree somewhat with the experimental result. Finally, the analytical result obtained using Freudenthal's fracture criterion does not agree with the experimental result. 相似文献
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Forming limit curves at neck and at fracture have been experimentally determined, and surfaces of fractured dome specimens have been observed optically and in the SEM, for an automotive AA6111-T4 sheet material. Various continuum ductile fracture criteria from the literature along with the assumptions of power law hardening, Hill’s quadratic yield criterion, and proportionality of stress and strain paths have been utilized for prediction of forming limit curve at fracture and compared with the experimental curve to assess the applicability of the different fracture criteria. The maximum shear stress criterion by Tresca predicts reasonably well the fracture limits of AA6111-T4 sheet material for a range of strain ratios, and is consistent with the microstructural observations. The criterion can be used to predict fracture limit curves from uniaxial tensile data and plane strain limit at fracture. A methodology for incorporating such a ductile fracture criterion into FE simulations of sheet stampings for prediction of fracture is discussed. 相似文献
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断裂力学判据存在的一个问题及讨论 总被引:7,自引:2,他引:5
利用细观力学对材料断裂机理的认识,结合脆性材料常规破坏试验结果,提出了一个新的拉断破坏条件,该拉断强度条件与常用的几何脆断强度条件相比,能更好地解释材料在复杂应力状态下发生的脆断与小塑性韧断,并对常用的断裂力学判据存在的问题进行了讨论,通过分析影响裂尖空穴扩张的主要因素,给出能适应不同应力状态的新的断裂判据。 相似文献
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PREDICTION AND CONTROL OF BOTH WRINKLE AND FRACTURE LIMITS ON CYLINDRICAL CUP MULTI-DEEP-DRAWING 总被引:3,自引:0,他引:3
Lei Junxiang Yantai UniversityKang Yonglin University of Science Technology Beijing 《机械工程学报(英文版)》1999,12(4)
0 INTRODUCTIONCylindricalcupdeepdrawingisboththemostcommonandrepresentativetechnologyinsheetmetalformingandtheimportanttestmethodsofevaluatingsheetformingproperties.Whenthedeformationquantityofcylindricalcupisgreaterthanforminglimitdeterminedwiththe… 相似文献