中文摘要：

对于断裂应变很小的混凝土类材料，在SHPB冲击试验中试样断裂前的应力是否达到均匀是冲击试验是否有效的一个关键。以水泥砂浆为例，采用弹性和ZWT粘弹性两种本构模型，通过特征线解法对高应变率SHPB试验过程中的加卸载应力均匀性进行了分析。发现入射波升时对脆性粘弹性材料的应力均匀性有影响，其中以τs／tL=2时最好，升时再延长反而对应力均匀化不利。采用不同升时加卸载时，应力幅值对于试样中应力均匀性没有影响，但对试样中应变和应变率的大小有影响。并且发现用常规的SHPB技术难以获得率相关脆性材料较可靠的应力-应变关系，但在应力均匀化后测得的动态断裂应力值是可靠的。

英文摘要：

As to concrete-sort materials, whether stresses have been uniformly distributed along the specimen before fracture occurs is a key issue. By using characteristics method of wave propagation, the SHPB tests for cement mortar which is modeled as ZWT viseo-elastie material and the elastic material separately are numerically studied in the present paper, to see how the stress is distributed during both loading and unloading. It is found that different rise-times of incident waves evidently influence the stress uniformity, and the optimum rise-time seems to be τs/tL=2, either shorter or longer rise-time will result in worse stress uniformity; the stress amplitude has no influence on the stress uniformity, but significantly influences the value of strain and average strain rate in specimens. The error found in the determination of dynamic stress-strain curve of rate-dependent brittle materials with the traditional SHPB teehuiques of either 3-wave method or 2-wave method, is actually unaeeepted, although the dynamic fracture stress can be correctly determined if the requirement of stress uniformity is satisfied before specimen fracture.