International Research Fellowship Program: Failure and Post-Failure Modeling in Concrete and Rock

0602080福斯特国际研究奖学金计划使美国科学家和工程师能够在国外进行9到24个月的研究。 该计划的奖项提供了联合研究的机会，以及使用独特或互补的设施，专业知识和国外的实验条件。福斯特博士与西班牙巴塞罗那加泰罗尼亚理工大学的哈维尔奥利弗博士一起工作。在不同的载荷条件下，各种材料都会出现局部变形模式。例子包括金属中的剪切带和颈缩，土壤中的压实和剪切带，陶瓷、混凝土和岩石中的开裂。已经提出了几种方法来预测这些变形模式在复杂的加载条件下的发病和传播。一种已经显示出很大潜力的方法是具有应变增强的有限元方法，该应变增强以可以在任意位置和方向穿过单元的破坏面的形式存在。 十多年来，各种形式的增强应变有限元已被用于模拟各种材料（包括混凝土和岩石）中的局部变形。这些元素中的大多数都集中在模拟一种类型的故障，如开放裂缝或剪切破坏和摩擦滑动。然而，在许多情况下，作用在结构上的荷载的性质可能随时间而改变。例如，混凝土坝在地震荷载作用下可能会在张力作用下开裂，但在反向荷载作用下，表面可能会在摩擦力作用下滑动。一个新的增强应变单元合成，可以考虑这些多个加载情况。该元素包括开放和横向自由度，帐户裂纹扩张由于剪切和粗糙不匹配，模型软化在所有制度，并占摩擦沿着封闭的表面。非线性材料模型，反映实际的材料行为的裂纹表面实施。材料模型，包括拉伸断裂和可变摩擦响应，从地质力学和混凝土研究，并修改，以最好地适合所调查的材料和应用。模型适用于岩石和混凝土中的问题，包括隧道，混凝土坝和其他大型结构在反向荷载下。

0602080FosterThe International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twelve-month research fellowship by Dr. Craig D. Foster to work with Dr. Javier Oliver at Polytechnic University of Catalonia, in Barcelona, Spain.Localized deformation patterns occur in a variety of materials under different loading conditions. Examples include shear bands and necking in metals, compaction and shear bands in soils, cracking in ceramics, concrete, and rock. Several methods have been proposed to predict the onset and propagation of these deformation patterns under complex loading conditions. One method that has shown a lot of potential is a finite element method with a strain enhancement in the form of failure surface that can pass through the element at an arbitrary location and orientation. Various forms of enhanced strain finite elements have been used for over a decade to model localized deformation in a variety of materials, including concrete and rock. Most of these elements have focused on modeling one type of failure, such as opening cracks or shear failure and frictional sliding. Under many situations, however, the nature of the loads on a structure may change over time. For example, concrete dams under seismic loading may crack in tension, but on reverse loading the surfaces may slide under friction. A new enhanced strain element is synthesized that can account for these multiple loading situations. This element includes opening and transverse degrees of freedom, accounts for crack dilation due to shearing and asperity misfit, models softening in all regimes, and accounts for friction along closed surfaces. Nonlinear material models that reflect actual material behavior are implemented for the crack surfaces. Material models that including both tensile fracturing and variable friction response are drawn from both geomechanics and concrete research, and modified to best fit the materials and applications under investigation. Models are applied to problems both in rock and concrete, including tunnels, concrete dams, and other large structures under reverse loading.