被动围压下钢纤维超高性能混凝土冲击压缩力学特性与损伤特征

Impact compression mechanical properties and damage characteristics of steel fiber ultra-high performance concrete under passive confining pressure

【目的】为了研究掺有钢纤维的超高性能混凝土(UHPC)在冲击压缩作用下的力学特性与损伤特征,【方法】基于被动围压的霍普金森压杆,保持冲击气压为0.4 MPa不变,分别测试得到不同钢纤维掺量、不同含水状态UHPC试样的应力—应变曲线,并对其峰值应力、应变、能量耗散特性、损伤演化特征进行分析。【结果】结果显示:钢纤维在UHPC中网状分布,发挥桥接作用使试样动态抗压强度提高,钢纤维掺量为1%时动态抗压强度达到峰值,后随掺量增加有所降低,极限应变变化趋势与动态抗压强度相反,饱和试样峰值应力低于干燥试样,约为干燥试样的80%。【结论】计算了试样在加载三阶段的能量耗散,发现钢纤维可以降低荷载做功。此外,结合耗散能定义了损伤变量D,分析了UHPC损伤演化三阶段,得到钢纤维对损伤演化的抑制作用。

[Objective]The mechanical properties and damage characteristics of the ultra-high performance concrete(UHPC)mixed with steel fiber under impact compression are studied herein.[Methods]On the basis of split Hopkinson pressure bar with passive confining pressure and keeping the impact pressure constant at 0.4 MPa,the stress-strain curves of the UHPC specimens with different steel fiber mixing amounts and water contents are tested and obtained respectively,and then their peak stress-strain and energy dissipation characteristics as well as the damage evolution characteristics are analyzed.[Results]The study result shows that the reticular distribution of the steel fiber inside UHPC plays a bridging role to make the dynamic compressive strength of the specimen improved,for which when the steel fiber mixing amount is 1%,the dynamic compressive strength reach the peak value and then is decreased to some extent,while the changing trend of the ultimate stain is opposite to that of the dynamic compressive strength.The peak stress of the saturated specimen is lower than that of the dry specimen and is about 80%of the dry.[Conclusion]The energy dissipations of the specimen in three loading stages are calculated,and then it is found out that the load acting energy can be lowered by steel fiber.Additionally,the damage variable is defined in combination with the dissipation energy and the three stages of the damage evolution of UHPC are analyzed,thus the inhibiting effect of steel fiber on damage evolution is obtained.