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The paper addresses special features of nonlocalized and localized fatigue damage in metals and alloys. The sizes of maximum fatigue cracks at a fatigue limit in metals and alloys of various grain sizes and strengths are analyzed. The authors discuss the linear and nonlinear fracture mechanics criteria that relate the fatigue crack sizes and the fatigue limits. The experimental values of the fatigue crack size are compared to those calculated by different criteria. Special features of initiation of nonpropagating fatigue cracks in the presence of stress concentrators are studied. [ABSTRACT FROM AUTHOR]

Polymer nanocomposites are particle-filled polymers in which at least one dimension of the dispersed particles is in the nanometer range. Dispersing nanosize particles in a polymer matrix induces superior mechanical properties compared to traditional macro fillers. Nanolevel reinforcement also affects the tribological properties and needs to be clearly understood before using in practical applications. Friction and wear characteristics of Nylon 6 nanocomposites under dry sliding conditions are reported in this paper. Nylon 6 with 5% organoclay was prepared by melt intercalation technique. The tensile behaviour is evaluated according to ASTM standards. A pin-on-disc type tribometer is used for evaluating the friction and wear behaviour. It is found that the Nylon 6 nanocomposites have superior tribological properties than unfilled polymer. Formation of uniform tenacious transfer layer by Nylon 6 nanocomposite on the counterface contributes to the reduction in coefficient of friction and specific wear rate. Nylon Nancomposites exhibited high wear resistance compared with the neat Nylon. [ABSTRACT FROM AUTHOR]

Mechanical behavior of ceramics and glass under local loading of specimens by an indentor is studied experimentally by a proposed test procedure. The effect of scratching on fracture resistance is assessed by comparing the test results obtained by two methods - edge fracture under scratching (S+EF method) and without scratching (EF method). Based on the analysis of experimental findings, the fracture mechanism of these brittle materials under such test conditions is discussed. [ABSTRACT FROM AUTHOR]

The tear resistance of polyethylene terephthalate film is characterized by the essential work of fracture method in mode I as a function of test speed and temperature. Attempts to extrapolate tearing resistance found by the method of essential work to commercial slitting processes are discussed. Limitations of the essential work of fracture method with regards to specimen size are evaluated. Based on the findings modifications to the test protocol are suggested. [ABSTRACT FROM AUTHOR]

A framework for damage mechanics of concrete is applied to simulate the nonlinear elastic deformation behavior of concrete using finite element method (FEM). A rather simple isotropic damage model containing essentially no adjustable parameters is shown to produce results in remarkably good agreement with sample experimental data: the damage law requires only the fracture energy to be defined completely. The model is achieved by introducing a damage surface that is similar to the yield function in the conventional theory of plasticity. A special form of damage surfaces is constructed to illustrate the application of the model. A new damage criterion, defined as an equivalent strain norm, is proposed, in order to take into consideration the asymmetric behavior of concrete. For verifying the FEM program including the model, deformations predicted by this model are compared with both the experimental ones for the concrete structural model and the ones calculated without application of the continuum damage mechanics. [ABSTRACT FROM AUTHOR]

The reinforced and toughened PP/PA66 in situ composites were prepared via extrusion-drawing-injection method. The relationship among composition, phase morphology and mechanical properties, together with their functional mechanism, was investigated. The results show that in the range of PA66 weight fraction (fw) from 0 to 20% and under the experimental processing conditions, the main changes in phase morphology of the composites with fw are that the number of in situ formed PA66 microfibers and remained PA66 particles increases with fw whereas the fiber transverse size and its dispersity decrease till fw = 15% and then increase. This can be attributed to the combined effect of break-up, coalescence and deformation of the PA66 phase in the PP phase in the course of extrusion and drawing. The tensile strength of composites has a maximum value at fw of 15% and Young's modulus increases with fw up to a plateau level, while impact strength continuously rises with fw, an effect which can be ascribed to the distinct dependence of these properties on the phase-morphological factors mentioned above. [ABSTRACT FROM AUTHOR]

The relation between flaw density and strength of ceramic or brittle materials were derived and applied to a commonly used testing method of four-point bending for determining the strengths of ceramic or brittle materials. Previous analysis failed to include the failures outside or at the inner loading positions for four-point test data. The present approach elevates such a constrain so that the relation applies to failures occurs at any points between the outer loading positions for four-point test data. [ABSTRACT FROM AUTHOR]