第1部分:A36钢弹塑性CTOD韧性的试样厚度效应本文描述了试样尺寸对A36钢断裂韧性行为影响的实验和分析研究结果，主要是在下过渡区。该区域超出ASTM E-399定义的平面应变极限，但在任何宏观纤维撕裂之前发生失效的区域。实验结果通过裂纹尖端张开位移（CTOD）三点弯曲试样获得，分析结果通过三维弹塑性有限元分析获得。两种试样尺寸，全厚度[31.8-mm（1.25-in.）厚度]和减薄厚度[12.7-mm（0.50-in.）使用首选的t X 2t X 8t试样尺寸对厚度进行了研究。第2部分:A36钢矩形和方形CTOD断裂试样的分析和实验比较矩形十字的分析和实验研究- 在A36钢上进行了截面（t*2t）和方截面（t*t）三点弯曲CTOD断裂试样。本研究是长期调查的一部分，旨在制定标准，以评估特定结构情况下的断裂敏感性，即压力容器和短裂纹结构钢（a/W&sime；0.15），其中必须使用方形CTOD试样。通常，矩形CTOD试样用于实验室试验，但用于可能存在浅表面裂纹的焊接件试验，或用于裂纹深度比为a/W&sime以外的其他结构应用；0.5，通常需要方形试样。本研究的目的是使用等效裂纹深度比（a/W=0.5）比较方形试样和矩形试样的CTOD断裂韧性结果。这项长期调查的下一阶段将研究浅裂纹试样的断裂行为（a/W&sime； 0.15).

Part 1: Specimen Thickness Effects for Elastic-Plastic CTOD Toughness of an A36 SteelThis paper describes the results of an experimental and analytical study of the effect of specimen size on the fracture-toughness behavior of A36 steel, primarily in the lower-transition region. This region is beyond the limits of plane-strain as defined by ASTM E-399, but in the region where failure occurs prior to any macroscopic fibrous tearing. Experimental results were obtained using Crack-Tip Opening Displacement (CTOD) three-point bend specimens, and analytical results were obtained using a 3-D elastic-plastic finite-element analysis. Two specimen sizes, full thickness [31.8-mm (1.25-in.) thick] and reduced thickness [12.7-mm (0.50-in.) thick], were investigated using the preferred t X 2t X 8t specimen size.Part 2: An Analytical and Experimental Comparison of Rectangular and Square CTOD Fracture Specimens of an A36 SteelAnalytical and experimental investigations of both the rectangular cross-section (t * 2t) and square crosssection (t * t) three-point bend CTOD fracture specimens were conducted on an A36 steel. This study is part of a long-range investigation aimed at developing criteria to evaluate the susceptibility to fracture in specific structural situations, i.e., pressure vessels and structural steels with short cracks (a/W≃ 0.15), where the square CTOD specimen must be used. Generally the rectangular CTOD specimen is used in laboratory testing, but for weldment testing where shallow surface cracks may exist or for other structural applications with crack depth ratios other than a/W≃0.5, the square specimen is often required. The objective of this study was to compare the CTOD fracture toughness results of square specimens with those of rectangular specimens using equivalent crack depth ratios (a/W = 0.5). The next phase of this long-range investigation will study the fracture behavior of specimens with shallow cracks (a/W ≃ 0.15).