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平面-应变裂纹终止断裂韧性K_(1a)是采用静态方法进行分析,由小试样予以测定的。为确定这类分析对在裂纹扩展-终止过程结束时的K作出的描述是否适切,已进行了大量研究。本文对这些研究作了评述,而且指出,目前广泛地将K_(1a)认作为材料的一种固有性能是合理的。考察了两类数据。第一类数据是在扩展-终止过程中测定的应变、裂纹速率及K测量值。据发现,在该过程的早期,裂纹速率a很高,而经过这一阶段,试样的行为仅可用动态分析予以描述。随着a的降低及裂纹自然终止,用静态分析便足以描述试样行为。(采用焦散线法对金属试样和环氧树脂试样显示大的裂纹跃进进行的测量可作为对此的解释)。应变和K值波动(一般幅度很小)持续进行到终止之时及终止后某一段时间,使得在确定K_(1a)时有某种程度的不确定性。为确定这种不确定性是否能在测定K_(1a)中造成明显的误差,对不同试验条件下进行的测量作了比较,发现K_(1a)与测量的方式无关,而且,在采用静态分析中的不确定性远小于材料的散布度。有人认为,在试样弹性区段所见的波动不通过塑性区传递到裂纹顶端的这一事实可能是静态计算的K_(1a)恒定不变的原因。本文还讨论了对动态分析中的阻尼进行适当处理的重要性。
Plane-strain crack ultimate fracture toughness K_ (1a) is analyzed by static method and measured by small test specimens. Much research has been conducted to determine the suitability of such analyzes for the K at the end of the crack propagation-termination process. The paper reviews these studies and points out that it is reasonable to recognize K_ (1a) as an intrinsic property of materials widely today. Inspected two types of data. The first type of data is strain, crack rate, and K measured during extension-termination. It was found that in the early stages of the process, the crack rate a was high, and after this stage the behavior of the sample can only be described by dynamic analysis. With the decrease of a and the natural termination of the crack, static analysis is sufficient to describe the sample behavior. (The caustic method for the measurement of large crack jumps in metal and epoxy specimens can be used as an explanation). Strain and fluctuating K values, which are typically small in magnitude, persist until termination and some time after termination, leaving some degree of uncertainty in the determination of K_ (1a). To determine whether this uncertainty can cause significant errors in the determination of K_ (1a), the measurements made under different experimental conditions were compared and it was found that K_ (1a) was independent of the mode of measurement and, in the case of static analysis The uncertainty in the far less than the spread of the material. It is believed that the fact that the fluctuations seen in the elastic section of the specimen do not propagate through the plastic zone to the tip of the crack may be the reason for the constant K_ (1a) of the static calculation. This article also discusses the importance of proper damping of dynamic analysis.