不同条件对聚碳酸酯缺口冲击强度测试结果的影响

以纯聚碳酸酯(PC)、阻燃PC和阻燃增韧PC试样为研究对象,研究了ISO 7391–2,ASTM D256和ISO180三种标准测试的悬臂梁缺口冲击强度差异,同时探讨了缺口制作方式和退火处理(135℃,2h)对缺口冲击强度测试结果的影响。结果表明,不同PC试样采用ASTM D256标准测试的缺口冲击强度较ISO 7391–2稍高,而采用ISO 180标准测试的缺口冲击强度最低。偏光应力仪和扫描电子显微镜测试结果表明,由于ISO 180标准规定的试样厚度相对较大,试样产生了过大的残余应力,加之阻燃PC中阻燃剂与PC的相容性较差,进而导致采用ISO 180标准测试的阻燃PC缺口冲击强度测试数据极低。实际应用中尽量选用断裂行程短、试样厚度大的ISO 180标准对改性PC试样的缺口冲击强度进行测试,其更能体现材料的缺陷和实际韧性。采用机铣缺口测试的缺口冲击强度稍高,而采用模塑缺口测试的缺口冲击强度离散系数小,数据稳定性更好。退火处理虽可消除试样的内部应力,但会导致试样边缘位置应力集中更加明显,退火处理后各试样的缺口冲击强度测试数据均大幅度降低。

Effects of Different Conditions on Notched Impact Strength Test Results of Polycarbonate

Taking pure polycarbonate(PC),flame retardant PC,and toughened flame retardant PC samples as objects,the differences of notched Izod impact strength of the three samples tested through standard ISO7391–2,standard ASTM D256,and standard ISO 180 were researched.Besides,the effects of different notching methods and annealing process(135℃,2 h)on the notched Izod impact strength test results were discussed.The results show that,the notched impact strength test data of different kinds of PC samples tested by standard ASTM D256 are slightly higher than those tested by standard ISO7391–2,the test data by standard ISO 180 are minimum.Polarizing strain gauge and SEM test results indicate that,excessive residual stress induced due to the larger sample thickness set in standard ISO 180 and poor compatibility between flame retardant and PC in flame retardant PC sample result in extreme low notched impact strength test data of flame retardant PC sample without toughening agent tested by standard ISO 180.Standard ISO 180 should be utilized as much as possible in testing the notched impact strength of modified PC sample,which can reflect more defects and actual toughness of materials.The notched impact strength value of molding notch method is little bit less than that of milling machine notch method,but the dispersion coefficient is less and the value stability is better.Although annealing can remove the interior residual stress,the concentrate of residual stress on the edge position of sample is more obvious,and large decrease on the notched impact strength of all samples occur after annealing.