重组竹横向准脆性断裂的断裂参数

Fracture parameters of bamboo scrimber’s transverse quasi-brittle fracture

重组竹是一种可再生的绿色建筑结构复合材料,具有结构致密均匀、力学性能高强稳定、尺寸因需而定、原材料利用率高等特点,在工程应用方面前景广阔。为研究重组竹横向准脆性断裂的断裂参数,对不同尺寸重组竹单边缺口(SEN)试样进行三点弯曲断裂试验,基于边界效应模型(BEM),引入平均粒径G这一重要的细观结构参量,建立重组竹细观结构与宏观力学性能之间的关系,由试验得到的峰值荷载Pmax计算重组竹横向准脆性断裂的断裂参数,包括抗拉强度ft和断裂韧度KIC。经正态分布分析得到重组竹断裂参数均值μf和μK,且在具有96%可靠性范围几乎覆盖了全部试验离散点,结果如下:ft=μf=216.36 MPa,KIC=μK=16.76 MPa·m1/2。并利用实验室常规尺寸试样预测重组竹断裂参数,与试验结果之间的误差仅为3.17%。此外,随着重组竹试样缝高比α的增加,其断裂参数先增大后减小。

As a renewable and green composite material for buildings,bamboo scrimber has the advantages of densified and uniform micro-structure,high strength,variable size and shape and high utilization rate of raw materials.Therefore,bamboo scrimber has a broad prospect in civil engineering.In order to study the quasi-brittle fracture of bamboo scrimber in the transverse direction,three-point-bending tests were carried out on single-edge-notch(SEN)bamboo scrimber samples with different sizes.Based on the boundary effect model(BEM)in fracture mechanics,a quantified relation between the micro-structure and the mechanical properties of bamboo scrimber was established by introducing an important micro-structure parameter—average grain size G.Its transverse fracture parameters including tensile strength ft and fracture toughness KIC were calculated by the peak loads Pmax obtained from the tests.Then,the normal distribution was adopted to obtainμf andμK,the mean value of the fracture parameters as well as to cover the experimental scatters with 96%reliability,with the result as follows:ft=μf=216.36 MPa,KIC=μK=16.76 MPa·m1/2.The fracture parameters can be predicted by normal-size samples in the laboratory,and the error between the predicted and tested results is only 3.17%.The fracture parameters tend to increase first and then decrease with the increase of crack length to sample height ratio.