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对于三点弯曲U形切槽梁二等分线上的张开应力,如果用Creager和Paris的经典近似公式计算,则其适用范围很小;而用我们修正的公式计算,其适用范围几乎函盖U形切槽二等分线上整个拉伸区。由张开应力在U形切槽二等分线断裂过程区长度上积分,然后除以该长度得到平均张开应力;当其达到临界值时就得到包含拉伸强度和断裂韧度两个材料参数的平均应力破坏准则;利用这一准则提出用三点弯曲U形切槽梁同时测定这两个材料参数的新方法。因此,只要在实验时,制作一系列切槽深度相等而根部曲率半径不同的待测准脆性材料的U形切槽梁,用三点弯曲加载并分别测得其临界荷载,在已知应力集中系数的情况下,应用平均应力破坏准则就得到一超定方程组,再用恰当的数值方法便可解出拉伸强度和断裂韧度两个未知数。
The open stress on the bisector of a three-point curved U-shaped notched beam is very small if it is calculated using the classical approximation of Creager and Paris. However, with our revised formula, its applicability is almost the same Cover U-shaped groove bisecting the entire stretch on the line. By the open stress in the U-shaped slot bisector bisecting the length of the process area integral, and then divided by the length to get the average open stress; when it reaches the critical value to obtain the tensile strength and fracture toughness of two materials The average stress failure criterion of the parameters is obtained. A new method of simultaneous determination of these two material parameters by using the three-point curved U-shaped slotted beam is proposed by using this criterion. Therefore, as long as a series of U-shaped slotted beams with equal depth of cut and different radius of curvature of root are to be tested during the experiment, three-point bending loads and their critical loads are respectively measured. After known stress concentration Coefficients, an overdetermined system of equations is obtained using the average stress failure criterion, and two unknowns of tensile strength and fracture toughness can be solved using the appropriate numerical method.