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在本研究中,应用了线弹性断裂力学(LEFM)的概念和技术以测定各种铸态及热处理球墨铸铁的显微组织的断裂韧性。本文所介绍的是单边缺口试样(SEN)和紧凑拉伸试样(CT)在-40℃及24℃时的断裂韧性数据。此外,还试验了高球化率(>80%)和低球化率(<25%)的铸铁。附加分析包括试样的断口和全相研究,以及裂纹张开位移(COD)曲线和强度因子Rsc的分析。一些主要的研究结果如下: (1)某些球铁的韧性随试样尺寸的增大而增大,这与高强度钢中所见到的情况大不相同; (2)蠕虫状石墨较多的球铁(球化率<25%,无片状石墨)与高球化率(>80%)球铁相比,其韧性没有明显的差别。但片状石墨则显著降低韧性; (3)当厚度均为0.83吋时,所有试验铸铁的断裂韧性参数都在K_Q=34.0±7.4Ksi·in(1/2)范围之内; (4)某些显微组织的平面应变断裂韧性有效值K_(1e)已得出,并可用于该种铸铁的安全设计; (5)球铁试样在平面应变条件或接近平面应变条件下试验时出现突进现象。除LEFM试验外,还进行了初步的动态撕裂冲击试验(DT)。原始数据表明,铸态铁素体DT试样(5/8吋厚)至断裂时在24℃约需要100呎磅硗?力—时间曲线表明为一种缓慢的撕裂。为了给球铁铸件提供一详尽的安全设计数据,还进行了附加研究。
In this study, concepts and techniques of linear elastic fracture mechanics (LEFM) were applied to determine the fracture toughness of various as-cast and heat treated ductile iron microstructures. This article presents the fracture toughness data for Single Notched Specimens (SEN) and Compact Tensile Specimens (CT) at -40 ° C and 24 ° C. In addition, cast iron with high spheroidization (> 80%) and low spheroidization (<25%) was also tested. Additional analyzes include fracture and all phase studies of the specimens, as well as analysis of crack open displacement (COD) curves and strength factor Rsc. Some of the main findings are as follows: (1) The ductility of some ductile irons increases with the size of the sample, which is quite different from what is seen in high-strength steels; (2) Of the ductile iron (spheroidization rate <25%, no flake graphite) showed no significant difference in toughness compared with the high spheroidization (> 80%) ductile iron. (3) The fracture toughness parameters of all tested cast irons are all within the range of K_Q = 34.0 ± 7.4 Ksi · in (1/2) when the thickness is 0.83 " Some of the microstructure of the plane strain fracture toughness K_ (1e) has been obtained, and can be used for the safety design of cast iron; (5) ductile iron specimen in the plane strain conditions or nearly flat strain test conditions when the sudden phenomenon. In addition to the LEFM test, a preliminary dynamic tearing impact test (DT) was also conducted. The raw data shows that as-cast ferrite DT specimens (5/8 inch thick) require about 100 psia to break at 24 ° C. The force-time curve shows a slow tearing. In order to provide ductile iron castings with a detailed safety design data, additional studies were conducted.