共查询到19条相似文献,搜索用时 140 毫秒
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对五种金属材料进行了裂纹扩展稳定性的实验研究,试件分别采用三点弯曲试件(3PB 试件)和紧凑拉伸试件(CT 试件).试验结果分别由载荷 P——位移Δ曲线斜率的变化,(dp)/(dΔ)——Δ曲线,和撕裂模量曲线验证“撕裂失稳准则”.实验表明该准则是非保守的,同时还表明材料撕裂模量曲线 T_(MAT)-Δ(?)有相当离散度. 相似文献
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本文提供了一种可以进行自增强处理的圆筒试样,通过实验用柔度法确定了该试样的表面裂纹的应力强度因子,介绍了含表面裂纹试样的柔度测试技术,导出了柔度与表面裂纹尖端前缘各点的应力强度因子的关系式,该式可作为各种含表面裂纹试样柔度法测表面裂纹 K_1因子的参考,本文还测定了不同自增强程度下,自增强圆筒的表面裂纹疲劳扩展规律。 相似文献
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用分片合成法计算3点弯曲圆梁裂纹试样的柔度 总被引:1,自引:0,他引:1
本文用分片合成法计算了两种3点弯曲圆梁的柔度.这种方法将圆梁剖分成若干片,把每片当成矩形截面的3点弯曲梁,再将各片的柔度合成得到圆梁的柔度.计算结果颇佳.这种方法可以推广应用于其它构形复杂的裂纹试样. 相似文献
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如图1所示的拱形三点弯曲试样易于从环管类构件上取样,试验也方便,因而是一种颇有实用意义的断裂韧度测试试样.陈篪等同志首先提出了这种试样,并用柔度法从实验标定获得了K_I 和BEC 数据.本工作报道拱形试样三点弯曲情况的K_I 和BEC及纯弯曲情况(图2)的K_I 计算结果.计算纯弯曲情况是为了用等效力系原理导出K_I 的一般表达式.文中K_I 均为无量纲形式K_I~*=(K_IBW~(3/2))/M,式中:B 为试样厚度;W=R_1-R_2为试样宽度;M 为裂纹平面上弯矩. 相似文献
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单试样三曲线法测定J积分阻力曲线及条件起裂值 总被引:1,自引:0,他引:1
用单试样三曲线法测定了16MnR 钢和某一焊缝金属的 J 积分阻力曲线及其条件起裂值,与标准的多试样测定结果基本吻合.实验表明,单试样三曲线的关联分析反映了带裂纹的三点弯曲试样的宏观断裂物理过程,裂纹的延性扩展符合幂函数规律. 相似文献
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应用新型数字激光动态焦散线实验系统,采用含预制裂纹的有机玻璃板试件进行落锤冲击实验,研究了含圆孔缺陷三点弯曲梁的动态断裂行为。通过实验得到了含圆孔缺陷三点弯曲梁裂纹尖端动态应力强度因子的变化情况、裂纹扩展速度的变化情况以及裂纹贯穿空孔的扩展情况等。实验结果表明:三点弯曲梁中的空孔位置对裂纹的扩展轨迹具有明显的导向作用;空孔位置的改变会影响三点弯曲梁的断裂时间;空孔位置的变化对空孔下方裂纹的扩展时间、扩展轨迹影响较小;在空孔位置居中的情况下,空孔上方裂纹的最大扩展速度大于空孔位置偏移时的情况。 相似文献
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随着金属材料大壁厚结构件在工程中的广泛应用,对其断裂韧度的厚度效应研究具有重要的科学意义和工程价值。本研究基于有限元和实验相结合的方法,对金属材料断裂韧度的厚度效应进行预测。首先,通过一组薄壁厚金属材料标准三点弯曲试验得到试样失效时的临界载荷值,并利用内聚力模型与基于虚拟裂纹闭合技术的裂纹扩展模拟方法得到裂纹扩展时的单元临界能量释放率。随后,以此临界能量释放率作为裂纹扩展的启裂准则门槛值,通过有限元计算得到不同试样厚度下裂纹启裂时的裂尖断裂参数随着厚度的变化规律。最后,为了验证有限元模拟结果的准确性,本研究进行了另外两组不同厚度下三点弯曲试样的断裂韧度试验,并将试验结果与有限元结果进行了对比,验证了有限元所模拟的断裂韧度厚度效应的准确性。本研究旨在,通过薄壁厚三点弯曲试样的实验结果结合有限元模拟工作,即可实现金属材料断裂韧度的整个厚度效应曲线,为任意厚度下金属材料断裂韧度预测提供一种可靠的研究方法,有益于缩减试验成本,为大壁厚工程结构件的失效预测提供依据。 相似文献
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Fatigue characterization of tire rubber 总被引:1,自引:0,他引:1
An investigation of the fatigue behavior of tire rubber was undertaken. The tire rubber used in this work is a blend of natural rubber and polybutadiene. It is vulcanized and filled with carbon black. Fatigue tests were conducted on edge-notched prismatic specimens subjected to tension–tension loading in a displacement-controlled machine. The maximum strain was 8% and the minimum strain was 0.8%. The waveform of the fatigue cycle was sinusoidal at a frequency of 10 Hz. Initial cracks of various lengths were cut into the edge of the rubber specimens with a sharp razor blade. The tearing energy was calculated during the test. A power law relation between the crack growth rate and tearing energy was obtained. The fatigue life of tire rubber was estimated based on the integration of the power law relations and the tearing energy versus fatigue cycles curves in conjunction with the value of the critical tearing energy at crack growth initiation. 相似文献
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In this paper, the incremental theory of plasticity is used in conjunction with the strain energy density criterion to determine the stress field in 4-in. wide test specimens containing 3 holes. These specimens, made from 0.04-in. thick sheets of 2024-T3 aluminum, also contained small collinear cracks emanating from the holes. The initial crack sizes varied from 0.15 to 0.26 in. Residual strength tests conducted with these specimens revealed that stable tearing occurred before failure. Analyses were performed to predict the stable crack extension and failure by plastic collapsed. Because of the complexities involved with nonlinear stress analysis combined with subcritical crack extension, the finite element method was used with the grid pattern adjusted for each increment of stable tearing. Reasonable correlation between the experimental data and predicted results was achieved. 相似文献
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《Theoretical and Applied Fracture Mechanics》1988,10(1):27-41
The study reported in this paper deals with the experimental determination of the effect of the two-phase microstructure of an aluminum-silicon alloy on the propagation of fatigue-induced fracture. The work involved the use of a computerized apparatus which applied four-point bending loads to test specimens inside the vacuum chamber of a scanning electron microscope (SEM). The use of the SEM allowed for the in-situ monitoring of the progression of the fatigue crack with respect to the microstructure of the material.A constant load amplitude fatigue test was established for the experimental system and an analytic model is proposed to predict the growth of the crack in the specimen using compliance measurements. In-situ tests were performed on a variety of test aluminum-silicon alloy specimens. Preliminary results show that a relationship exists between the silicon phase in the aluminum matrix and propagating fatigue crack. Data from these tests were used to evaluate both the model mentioned above and an analytic relation for the stress intensity factor for a beam containing a crack subjected to four-point bending. 相似文献
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论文针对中密度聚乙烯材料(MDPE),采用平板试样进行了I型疲劳裂纹扩展和单次过载下裂纹扩展试验.发现与金属材料类似,单次拉伸过载对聚乙烯(PE)的疲劳裂纹扩展有明显的迟滞作用,降低了裂纹扩展速率.试验还通过变载荷刻线法获取疲劳裂纹扩展前缘的实际形貌和变化规律,对常规变载荷刻线方法进行了调整和验证,其修正方法对高分子材料的疲劳裂纹扩展前缘刻线具有较好的效果.通过观察发现含楔形塑性区的裂尖钝化是裂纹迟滞的主要原因.过载引入的塑性区内残余应力对裂纹迟滞也起了重要作用.论文利用Dugdale模型计算了塑性区尺寸,使用基于残余应力的Wheeler模型对过载迟滞进行了很好的拟合. 相似文献
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The stable tearing behavior of 2.3-mm thick sheets of 2024-T3 aluminum alloy was experimentally investigated for middle crack tension specimens having initial flaws that were: (a) flat fatigue cracks (low fatigue stress) and (b) 45-deg through-thickness slant cracks (high fatigue stress). The critical CTOA values during stable tearing were measured by two independent methods, optical microscopy and digital-image correlation. Results from the two methods agree well.The CTOA measurements and observations of the fracture surfaces have shown that the initial stable tearing behavior of low and high fatigue stress tests is significantly different. The cracks in the low fatigue stress tests underwent a transition from flat-to-slant crack growth, during which the CTOA values were high and significant crack tunneling occurred. After crack growth equal to about the thickness (a>B), CTOA reached a constant value of 6 deg and after crack growth equal to about twice the thickness (a>2B), crack tunneling stabilized. The cracks in the high fatigue stress tests reach the same constant CTOA value after crack growth equal to about the thickness, but produced only slightly higher CTOA values during initial crack growth. The amount of tunneling in the high fatigue stress tests was about the same as that in the low fatigue stress tests after the flat-to-slant transition.This study indicates that stress history has an influence on the initial portion of the stable tearing behavior. The initial high CTOA values, in the low fatigue crack tests, coincided with large three-dimensional crack front shape changes due to a variation in the through-thickness crack-tip constraint. The measured CTOA reached a constant value of 6 deg for crack growth of about the specimen thickness. This coincided with the onset of 45-deg slant crack growth and a stabilized, slightly tunneled (about 20 percent of the thickness) crack-front shape. For crack growth on the 45-deg slant, the crack front and local field variables are still highly three dimensional. 相似文献
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E. Smith 《Theoretical and Applied Fracture Mechanics》1985,4(1):53-57
The stability of crack growth in a beam subject to combined bending and tensile loadings is examined for the case where the material is very ductile and where the beam is built-in at one end. Application of a displacement at the free end, and variation of the angle which the displacement makes with the beam, allows the combined effects of bending and tensile loadings on the stability of crack growth to be assessed. The stability analysis is based on the tearing modulus procedure, and the general conclusion is that tensile loadings can promote crack instability. 相似文献