Crack formation Fracture mechanics

Hillerborg, A., Modeer, M. and Petersson, P.E. (1976). Analysis of crack formation and crack growth in concrete by means of fracture mechanics and finite elements. Cement Concrete Res. 6, 773-782. 

Most of the technical raw materials used in solid reactions are polycrystalhne, and these - when in solid form - undergo a range of modifications during milling. The first observation is the fracture of the solid into smaller pieces. The fracture mechanics are a topic of discussion, and fracture can be divided into two steps, namely crack formation and crack propagation . Depending on the ability of the material to undergo plastic deformation before fracture, either brittle or ductile fracture can be defined ... 

The question rise whether the behaviour described can be evaluated on a fracture mechanics basis. The critical energy release rate associated with the formation of a transverse crack is technically difficult to measure. As a first approximation, it is possible to use the critical energy release rate obtained from a double cantilever beam fracture mechanics test (DCB). This test concerns the growth of a delamination between two layers (mostly oriented ai 0°) in opening mode I. Tests performed on the same carbon-polyetherimide at 0°/0° interface as in this study were reported recently [9] and gave a value of 1200 J/m. ... 

Fracture surfaces of the cyclically deformed fatigue specimens were observed at low magnification in order to identify the zones of fatigue initiation and final failure, at higher magnifications in order to identify the regions of microscopic crack formation and growth and microscopic plastic mechanisms. 

Of the layers mentioned above, the thin films showing the widest range of stress are the PECVD oxides. The stress state of the oxide layers becomes important when such films are used as part of a membrane or as a passivation layer. Membranes that are under considerable compressive stress tend to buckle, severely changing their mechanical properties. In contrast, considerable tensile stress in membranes can lead to crack formation and fracture. The passivation properties of PECVD oxide layers, for example, towards humidity, depend sensitively on their composition, which, in turn, has a great influence on the stress. 

Crack Formation and Fracture of a Material in Terms of Fracture Mechanics... 

Karimov, I., Mechanics of Crack Formation at Fracture of a Concrete (literature review) http //www.masterbetonov.ru/content/view/528/239. 

The failure of an adhesive joint can be considered to involve the initiation and propagation of naturally occurring (intrinsic) flaws or defects. Fracture mechanics is the field of mechanics concerned with the study of the formation and propagation of cracks in materials. The objective of using fracture mechanics is to determine the bond durability of a specific adhesive and provide a basis for estimating the fracture, fatigue, and service life of the adhesive joints. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the resistance of a material to fracture. 

---