考虑裂尖约束效应的小尺寸CIET试样延性断裂行为

应用单试样规则化法完成了压力容器用钢SA-508紧凑拉伸(Compact tension,CT)、三点弯曲(Single edge-notched bending,SEB)和小尺寸含内侧边裂纹C形拉伸(C-shaped inside edge-notched tension,CIET)三类试样的延性裂纹扩展行为试验,获得了J-Δa阻力曲线。结果表明,SA-508钢的J-Δa阻力曲线受试样构形和裂纹尺寸的影响较大,其根本原因在于试样裂纹尖端约束不同而引起延性断裂行为差异。引入J-Q-M三参数约束理论考察断裂试样的裂尖约束效应,采用权重平均法求解与距离无关的约束参数Q。弹塑性有限元分析结果表明,平面应变条件下的Q参数与载荷水平无关,但三维条件下的Q参数却仍受载荷水平的影响。基于J-Q-M三参数约束方法,建立三类试样满足J-Q-M控制的有效尺寸条件。进一步地,结合条件启裂韧度J0.2BL、J0.5BL试验结果和J-Q-M理论,获得了基于Q参数的约束修正J-Δa阻力曲线簇,可用于任意约束试样以及实际含裂纹结构的延性断裂行为预测。

文化生态学视角下古镇保护与开发策略研究——以绵阳市三台县郪江古镇为例

从文化生态学的角度出发,提出古镇的文化生态圈层结构,分别对郪江古镇的文化要素、空间格局和行为方式等文化生态资源要素进行分析.进而阐述古镇的文化生态进化过程中封闭性和聚落活力的改变,指出古镇文化生态的被入侵、多样性锐减、群落老化等现象和问题,最终提出从文化生态的多样性、共生性、系统性和可持续性4个方面来进行古镇保护与开发的具体策略与建议.

Estimation of J—R Curves for Small-Sized COEC Specimens and Its Application Considering Crack-Tip Cons tr aints

The normalization method has been employed to estimate the J-resistance (J—R) curves for C-shaped outside edge-notched compression (COEC) specimens of SA-508 steel. The COEC specimens present the lowest J—R curves in comparison with other three types of specimens. Based on the J—Q—M met hod, the constraint parame ter Q determined at the mid-plane in the through-thickness direction of the specimen is used to approximately quantify the threedimensional crack-tip constraint for COEC specimens. Combining with the previous experiments on J—R curves, the constraint-coirected J—R curves for SA-508 steel specimens are given, which may be used to predict the fracture toughness of actual cracked components in structural integrity assessment.