考虑尺寸效应影响的准脆性材料断裂特性

Fracture properties of quasi-brittle materials considering size effect

为研究尺寸效应对准脆性材料抗裂性能的影响,以石膏为研究对象,对直径分别为60、100、150、200 mm的半圆弯曲(semi-circular bend,SCB)试样和中心直裂纹半圆弯曲(notched semi-circular bend,NSCB)试样进行了三点弯曲加载,分析了尺寸效应影响下准脆性材料的断裂特性演化规律,包括荷载-位移曲线、抗拉强度(σ_(t))、断裂韧度(K_(ⅠC))、断裂能(G_(f))和断裂过程区长度(r_(c))。结果表明:2种试样的荷载-位移曲线形态基本一致,表现为典型的脆性破坏;预制裂纹的存在降低了试样承载能力,相同尺寸下SCB试样的峰值荷载约为NSCB试样的5.57~6.25倍;σ_(t)随试样直径的增大逐渐降低,而K_(ⅠC)呈现相反的规律,尺寸效应对σ_(t)的影响更显著;极限裂纹张开位移随试样尺寸的增大逐渐增大,G_(f)与试样直径具有良好的线性关系;大尺寸试样具有较大的r_(c)值,且r_(c)与韧带区长度的比值随试样尺寸的增大而增大。

To study the influence of the size effect on the fracture resistance of quasi-brittle materials,three-point bending loading were conducted on semi-circular bend(SCB)specimens and notched semi-circular bend(NSCB)specimens using gypsum with diameters of 60,100,150 and 200 mm as the model material.The evolution law of fracture properties of quasi-brittle materials under the influence of size effect was analyzed,including load-displacement curve,tensile strength(σ_(t)),fracture toughness(K_(ⅠC)),fracture energy(G_(f))and fracture process zone length(r_(c)).The results show that the load-displacement curves of the two specimens are basically the same,showing typical brittle damage.The presence of prefabricated cracks reduces the load carrying capacity of the specimens,and the peak load of the SCB specimen is about 5.57-6.25 times that of the NSCB specimen at the same size.σ_(t)gradually decreases with the increasing specimen diameter,while K_(ⅠC)shows an opposite trend,and the effect of size onσ_(t)is more significant.The maximum crack top opening displacement gradually increases with increasing size,and G_(f)has a good linear relationship with the specimen diameter.Larger specimen size leads to larger r_(c)values,and the ratio of r_(c)to ligament zone length increases with specimen size.