Fracture toughness test

Fig. 6. Fracture toughness test specimens (a) single-edge notch (b) center notch (c) compact tension and (d) three-point bend. Terms are defined in text.

In metals, inelastic deformation occurs at the crack tip, yielding a plastic zone. Smith [34] has argued that the elastic stress intensity factor is adequate to describe the crack tip field condition if the inelastic zone is limited in size compared with the near crack tip field, which is then assumed to dominate the crack tip inelastic response. He suggested that the inelastic zone be 1/5 of the size of the near crack tip elastic field (a/10). This restriction is in accordance with the generally accepted limitation on the maximum size of the plastic zone allowed in a valid fracture toughness test [35,36]. For the case of crack propagation, the minimum crack size for which continuum considerations hold should be at least 50 x (r ,J. 

Cutwater, J. O., Murphy, M. C., Kumble, R. G. Berry, J. T. (1974). Double torsion techniques as a universal fracture toughness test method. Fracture Toughness and Slow-Stable Cracking, ASTM Special Technical Publication 559, pp. 121-31, American Society for Testing and Materials. 

Fracture strength, of vitreous silica, 22 428 Fracture tests, 1 514 Fracture toughness ceramics, 5 619-623 of silicon carbide, 22 528t of vitreous silica, 22 429 Fracture toughness tests, 10 427 Fracture toughness values... 

Figure 2. Typical Load-Displacement (left) and Potential-Drop-Crack-Length-Measurement (right) Records Acquired During Fracture Toughness Test of Forged Stainless Steel.

Pig. 1 a and b. Fracture toughness test specimens a three-point bend and b compact tension. Pre-crack length denoted by a. Movement of crosshead is vertical for both... 

The fracture properties of foods have been extensively studied and comprehensive reviews (64 and references therein) exist that address testing and application of fracture data in the food industry. As mentioned earlier, in the food industry compression tests are viewed also as fracture tests and the yield stress is often regarded as the fracture stress. However, in this review, the discussion is confined to only those types of fracture tests that lead to estimates of the fracture toughness and not the yield stress. The fracture toughness tests are relatively recent in the food industry. 

A number of different fracture toughness tests have been applied to foods including, the microtome test (65), the wedge fracture test (66-68) and tension tests (69). The 3-point bend test was applied by Charalmabides et al (70) in testing Cheddar cheeses. 

Fracture surfaces after fracture toughness tests... 

McClintock FA, Irwin GR (1964) Fracture toughness testing and its applications. ASTM, Philadelphia, ASTM STP 381, p 84... 

A DROP TOWER METHOD FOR HIGH RATE FRACTURE TOUGHNESS TESTING... 

A Drop Tower Method for High Mte Fracture Toughness Testing of Polymers... 

Essential Work of Fracture and Cohesive Zone Fracture Toughness, Testing protocol prepared for ESIS TC4 by E. Clutton and revised by D.R. Moore (July 2002). 

In the present work, a novel experimental method was proposed to evaluate the modes I-fll fracture toughness of the adhesive interface between concrete and carbon fiber sheets. The validity of the evaluation formula was studied on the basis of the results of finite element analysis. The mixed mode fracture toughness and fracture criterion of the adhesive interface were also studied on the basis of the results of fracture toughness test using the proposed method. 

Fig. 12. Experimental apparatus of the mixed mode fracture toughness test.

The mixed mode fracture toughness tests were carried out on a universal testing machine at loading rate of 1 mm/min. The loading angle was varied to study the criterion of mixed mode fracture as = 0°, 15°, 30°, 90° (G /G=0.01, 0.31, 0.55, 0.95). 

Figure 13 shows a typical result of fracture toughness test. The abscissa shows the displacement of crosshead. The ordinate shows the load applied to the specimen. 

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