超塑性材料约束胀形中的空洞损伤与变形局部化

将含有二阶段空洞长大模型的本构关系引入大变形刚黏塑性有限元中，研究了空洞敏感材料向锥台形凹模内超塑约束胀形时空洞化损伤与变形局部化行为，详细阐述静水背压Ｐｈ、初始空洞长大速率β＿０以及模具几何形状（锥角θ，模腔高度Ｈｐ）对局部化以及空洞断裂行为的影响，给出实现完全贴模条件下Ｐｈ－θ，Ｐｈ－β＿０，Ｈｐ－θ以及Ｐｈ－Ｈｐ间临界关系。     

Characterization of dissipation losses in cement paste with diffuse ultrasound

The objective of this study is to quantify the dissipation losses in cement paste using diffuse ultrasound, and then to relate these results to the corresponding values measured with a coherent ultrasound procedure. The results show a linear dependency on frequency for this energy dissipation (intrinsic absorption), and exhibit a reasonable correlation between the dissipation losses and the amount of cement paste present in a sample. In addition, there is good agreement between the air content predicted with diffuse ultrasound, and that directly measured with a standard optical technique.