Fracture analysis diagram

During the last twenty years, there has been an increasing awareness of the danger of brittle fracture of steel vessels at ambient temperatures, largely as a result of the work of Pellini and Puzak at the Naval Research Laboratory and their investigations of failures of World War II ships. Their "Fracture-Analysis Diagram" (Figure 3-1) shows that a small flaw can initiate brittle fracture at tern-... 

Figure 3-1 Fracture analysis diagram. Reprinted with permission from Naval Research Laboratory Report 5920, Fracture-Analysis Diagram Procedure For the Fracture Safe Engineering Design of Steel Structures, W.S. Pellini and P.P. Puzak, Figure 9, p 8 (March 15 1963).

Pellini, W.S., and Puzak, P.P., Fracture Analysis Diagram Procedure For The Fracture-... 

PelliniW and Puzak P (1963), Fracture analysis diagram procedures for the fracture-safe engineering design of steel structures, NRL Report 5920, Naval Research Laboratory, Washington, DC. 

ASME Code Section III at first used the fracture analysis diagram (FAD) for the prevention of brittle fracture. Linear elastic fracture mechanics was introduced in 1972 Summer Addenda, Appendix G. ASME Code Section XI Appendix A and NRC Federal Register lOCFR Part 50 were issued in 1973. In these codes and regulations, RTndt was introduced as an important index temperature to characterize the transition curve of fracture toughness. 

In testing the specimens, deflection can be limited such that the stress at failure does not exceed the yield value. Thus, a direct correlation is established between the NDT temperature and )deld stress. Such information is used in constructing the fracture analysis diagram (FAD). 

Forming Limit Analysis. The ductihty of sheet and strip can be predicted from an analysis that produces a forming limit diagram (ELD), which defines critical plastic strains at fracture over a range of forming conditions. The ELD encompasses the simpler, but limited measures of ductihty represented by the percentage elongation from tensile tests and the minimum bend radius from bend tests. 

It has been shown that fracture is a very complex process and the fracture performance depends on both the initiation and the propagation of a defect [6-10] in the material. Under impact, most polymers break in very distinct manners. Several types of fracture have been identified depending on the amount of plastic deformation at the crack tip and the stability of crack propagation. For each type, an appropriate analysis has been developed to determine the impact fracture energy of the material. These methods have also been verified in various plastics [11,12]. The different fracture behaviors in most polymers are illustrated in Figure 27.1, which shows a schematic drawing of the load-deflection diagram of Charpy tests on HIPS [13] under an impact velocity of 2 m/s at various temperatures. 

As shown above, the ZrO/Ni composites examined by disk-bend testing are found to deform in a nonlinear manner, so that composition-dependent fracture strengths cannot be obtained directly from the stress-strain diagram in Fig. 3. Under the circumstances, we now make a micromechanical analysis to estimate actual stresses to be developed by plastic deformation of the ductile constituent on the basis of an established "mean-field" model [12]. In the following, the macrostress a) is related to the microstresses and (o) such... 

Independent of the test methods applied and the respective results, a precise analysis of the failure source is required. Here, fracture-type time-diagrams are used in which an allocation of failure sources is made over the test period (adhesion fracture, cohesion fracture, adherend fracture, corrosion, q.v. Figure 7.8 and Figure 10.7). 

Figure 12. Diagram showing the analysis used in linear fracture mechanics to determine the energy input, work done, and energy stored in a linear elastic material.

They can be plotted as the so called Mohr failure envelopes in the cr-r diagram together with Mohr s circles and employed for analysis of stability of fractures or faults under given stress conditions. If the outer Mohr s circle touches the failure envelope, there is one fracture or fault which is unstable and can fail, its orientation being defined by inclination 6 of the fault fi om the maximum stress direction (see Fig. 5a). 

---