SIZE EFFECT AND REVISION OF K_(1c) IN SENB METHOD
SENB 方法中 K_(1c)的修正与尺寸效应

Single-Edge-Notched-Beam(SENB)method is rather popular and simplefor measuring the fracture toughness of ceramic materials,but it is not perfect enough intheory.Experiments show that the toughness value measured by SENB method is relatednot only to the size of specimen and experimental condition but also to the calculating for-mula.In this paper,tbe formula was discussed and revised,the mean fracture stress in therupture origin zone was put forward to replace traditional fracture strength.It was pointedout that the specimen with different size must coincide in shape.The size effect of K_(lc)hasbeen studied and theoretical relation between K_(lc) value and size of specimen has been de-rived.The fracture tonghness of several sets of shecimen with different size wasmeasured,including Al2_O_3and hot-pressed Si_3N_4ceramic materials.The experimental resultswere utterly identical with theoreitical curve.Theoretically,the fracture toughness,K_(lc),is amaterial constant in any case,but the K_(lc)measured by specific method is under the influenceof the shape and size of sprcimen.Experimental and theoreitical analysis indicate that thereexists a critical size on which K_(lc)measured as maximum.