[en] The necessary and sufficient conditions for characteristic integrals of fracture mechanics to be independent of area (or integration path), without making any assumptions concerning the behavior of the material are defined. The principle of the method involves comparing the spatial variation in energy density received with that which would result from a spatial variation in strain alone. This introduces a defect vector at each point of the solid. The resultants of the total defect vectors situated within an area are the characteristic integrals of this area. The condition governing independence in a region requires that the defect vector be null at any point. This condition in set under different forms which actually state that the energy density per unit volume received must have the same form of variation in space as in time

[en] Short communication

[en] Fracture Mechanics introduces in the mechanics of solids surfaces along which displacements are discontinuous, or cracks, which result in singular solutions. The conditions for fast fracture, or crack instability, is expressed by writing that the strain energy released by a virtual extension of the crack is at least equal to the energy necessary to that extension. If calculations are limited to the first term, singular, of the stress field near the crack tip, the instability condition is written in terms of a unique parameter, the stress intensity factor, which depends on the load and geometry data. The conditions of validity of this theory are examined, with the introduction of a plastic strain zone near the crack tip, and the practical possibilities of fracture prediction. A particular application to pressure vessels is given, in plane strain for heavy walls, in plane stress for thin vessels

[en] We present an energy approach of stable crack growth problem in three dimensional situations. The associated behaviour is determined for the 2618 T6 alloy and prediction of 'four point' bending tests is performed and compared with experiment. Finally we show how the bifurcation problem can be delt with the same formalism

No abstract available

[en] The behavior of non-traversing crack in a ductile strain-hardenable material used in relatively thin structures is analyzed. The investigations dealt with the growth of cracks under the effect of fatigue and creep, and with the determination of critical conditions leading to fracture of the ligament. The principle of the method used involves localizing and then virtually eliminating the portions of the structure in a plastic state, followed by treatment of the remaining portion by means of standard elasticity equations, by imposing appropriately limited conditions at the boundaries of the eliminated plastic regions

[en] The results presented give some guidance on the selection of the toughness measurement technique for tetragonal zirconia ceramics. Two main points are concluded: for tetragonal zirconia ceramics, the toughness techniques SENB (100 μm) and CVN (280 μm) give good comparative results regardless of the degree of stress induced transformation shown by the ceramic; toughness measurement techniques using diamond indentation (DCM and ISB) are sensitive to the level of stress induced transformation. Toughness values using these techniques should be considered only for comparison in materials where a clear crack pattern is evident and the toughness is independent of the indentation load. (author)

No abstract available

[en] Dynamic fracture toughness of simulated HAZ of a structural steel(equivalent to KS D3503) was investigated by instrumented impact testing technique. According to the validity criteria of this testing method, the measured fracture toughness values of this steel were evaluated to be valid when tested at temperatures lower than -40 deg C for fine grained HAZ and lower than -10 deg C for coarse grained HAZ, respectively. Even though the coarse grained HAZ fails in brittle manner at fairly low temperatures, the specimens must be fatigue precracked to obtained valid results. (Author)

[en] Multilayer glass fiber reinforced polymer (GFRP) laminates filled with nanoclay was manufactured with compression moulding machine. In the present work, five kinds of nanoclay (Cloisite 25A) loadings viz. 2, 4, 6, 8 and 10% on weight basis of epoxy resin were employed to modify the interlaminar shear strength (ILSS), critical energy release rate (GIc) and impact energy properties of GFRP laminates. Experimental results obtained from ILSS test on clay filled GFRP confirm that the superior strength was attained at low clay content of 155.10 MPa. Furthermore, the mode I interlaminar fracture toughness test conducted on DCB specimens revealed that the commanding improvement of GIc was obtained at 2 wt.% clay content level. On the other hand, both ILSS and fracture toughness was getting reduced at higher clay loadings. At last, the impact strength of the test samples was investigated by using Izod impact test apparatus and observed that the impact energy was increased by 44.39% for 2 wt.% and followed by 24.87% for 4 wt.% clay loadings. (paper)