强度破坏点后岩石应力-应变曲线荷载速率依存性研究

LOADING RATE DEPENDENCY OF STRESS-STRAIN CURVE IN POST-FAILURE REGION OF ROCKS

利用3种试验方法对在强度破坏点之后处于低应力下的岩石应力-应变曲线的荷载速率依存性进行研究。首先,对三城目安山岩、稻田花岗岩和田下凝灰岩进行交替变换荷载速率试验,按一定应变间隔Δε,对同一个试样交替施加高低2种不同的荷载速率,得到对应于2种荷载速率的应力-应变曲线。试验结果表明,在破坏点之后仍可以清楚地观察到应力-应变曲线的荷载速率依存性。其次,对三城目安山岩和稻田花岗岩在恒定速率下进行循环加载卸载试验,得到了应力-应变曲线上很多点处的卸载曲线。将在交替变换荷载速率试验中得到的对应于低荷载速率的应力-应变曲线沿着卸载曲线平移,可以与高荷载速率对应的应力-应变曲线重合。最后,对三城目安山岩、稻田花岗岩和田下凝灰岩进行组合试验,即对一个岩石试样施加2种交替变换荷载速率和循环加载卸载。结果表明组合试验具有操作简单性和很强的适应性,可以用来研究岩石强度破坏点处以及强度破坏点之后领域的荷载速率依存性,强度破坏点之后的应力变化率与强度点处的基本一致。

The loading rate dependency of stress-strain curve at very low stress level in the post-failure region is investigated with three testing methods.A testing method,in which a single rock sample is loaded at alternating loading rate with a predetermined strain intervalΔε,is applied to Sanjome andesite,Inada granite and Tage tuff. With this method,two stress-strain curves corresponding to the two loading rates can be obtained.Experimental results indicated that loading rate dependency of stress-strain curve was clearly observed up to the very low stress level in the post-failure region,where failure progressed considerably.Next,unloading-reloading cycles are repeated in constant loading rate test with Sanjome andesite and Inada granite;and unloading curves at many points along stress-strain curve are obtained.Stress-strain curve at slow loading-rate obtained in alternating loading rate test is shifted along the unloading curves,and then it overlapped on stress-strain curve at a fast loading rate.A new testing method,in which alternating two loading-rates and unloading-reloading cycles are repeated with a single rock sample,is proposed and applied to Sanjome andesite,Inada granite and Tage tuff.It is found that the new testing method is easy to conduct and suitable for investigating loading rate dependency of peak strengthand that of post-failure region of rocks.The percentage of change of stress in post-failure region is almost equal to that of the peak strength.