A combined theoretical and experimental study of the criteria governing the failure analysis of pressure vessels with defects has been performed. The fields of fracture mechanics (linear elastic and elastic-plastic behaviour), failure governed by large scale plastic deformation and energy balance methods are critically reviewed. All three approaches are shown to have relevance in the complete failure analysis of a structure with defects. An experimental study of the failure mechanisms of precracked polycarbonate and maraging steel plates and model polycarbonate vessels is presented. Room temperature, static loading tests are performed on 85 mm wide, 5 mm thick compact specimens of polycarbonate (0.013 andle; <sup>a</sup>andfrasl;<sub>W</sub> andle; 0.810). For comparison, 51 mm wide maraging steel compact specimens are monotonically loaded at room temperature. The influence of through-thickness constraint on the fracture toughness and slow crack growth characteristics of the steel is investigated using plates of varying thickness (3.1 mm-25.4 mm) and initial crack length (0.386 andle; <sup>a</sup>andfrasl;<sub>W</sub> andle; 0.766 for 3.1 mm thick sheet); various ancillary studies (scanning electron microscopy, surface deformation studies) complement the results. The crack growth behaviour of longitudinal through (0.704 ≤ c / andradic;‾DT/2</span> ≤ 1.434) and deep part-through (<sup>d</sup>andfrasl;<sub>T</sub> = 0.700 and 0.878) cracks in 50.8mm and 102mm diameter (5mm and 6mm wall thickness) polycarbonate cylinders is also studied. Bowling and Townley's two-criteria approach to failure i.e. LEFM on the one hand and limit analysis on the other, is shown to provide a useful method for assessing the relative importance of crack initiation, in the presence of limited crack tip plasticity and general yield as failure criteria for a given sized defect. Thus, for crack tip plasticity fully contained by an outer elastic field i.e. not general yield, the LEFM parameter, K<sub>Ic</sub> (with the possibility of a plasticity correction factor for thin sheet) can be used to predict crack initiation. For the low strain-hardening maraging steel, Irwin's plane strain plasticity correction, <sup>1</sup>andfrasl;<sub>6π</sub> (K<sub>Ic/σ<sub>y</sub></sub>)<sup>2</sup> is shown to be applicable to sheet thicknesses comparable to <sup>1</sup>andfrasl;<sub>π</sub> (K<sub>Ic/σ<sub>y</sub></sub>)<sup>2</sup> i.e. twice Irwin's plane stress plastic zone radius.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:459336 |
| Date | January 1978 |
| Creators | Hodkinson, Pauline H. |
| Contributors | Ruiz, Carlos |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://ora.ox.ac.uk/objects/uuid:28499f85-1968-412e-a139-e3f6bc6af439 |
Page generated in 0.0187 seconds