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Layered composites composed of two or more dissimilar metals can be easily created with precisely controlled layer thickness (to within one atomic layer) by various vapor deposition techniques. For equithickness composites with layer thicknesses greater than 100 nm, typically, flow strengths display a Hall-Petch type dependence on layer thickness, i.e., σ_Y = kh^−1/2 + σ_0, where h is the layer thickness, k the Hall-Petch constant and 0, a background strength or friction stress. For composites with thinner layers this relation is no longer obeyed, but instead the strength becomes less dependent on h and reaches a maximum at an h of about 1 – 5 nm, as shown in Figure 1, Misra, et al [ 1 ]. Although, at maximum, the strength is lower than predicted by Hall-Petch, these materials are still very strong, with flow strengths exceeding 1 GPa and, in some cases, approaching the theoretical shear strengths of the constituents. Even at these high strength levels the materials are deformable, plastically. Cu/Nb, for example is easily rolled to large reduction in thickness except as noted below, Misra [ 2 ].

We have examined the effect of dislocation sources introduced on the surface of single-crystal and polycrystalline tungsten on the plastic flow and fracture behavior at temperature in the range 77 K to 590 K. The experiments utilize the phenomenon of surface film softening observed in many body-centered cubic metals, such as observed by Sethi and Gibala [ 1 – 3 ]. In investigations like these, it is observed that application of surface films of approximately 50–200 nm in thickness to bcc metal substrates can decrease the yield and flow stress, increase the ductility, and correspondingly reduce the large temperature dependence of the yield and flow stress at homologous temperatures T below approximately 0.15T_m, where T_m is the absolute melting temperature. The large temperature dependence of the yield and flow stress at T/T_m < 0.15 is associated with the high Peierls-Nabarro stress of screw dislocations in the bcc structure. By contrast, edge dislocations in bcc metals have high mobility at low temperatures. Mechanistically, it has been shown that for the coated materials under applied stress, large densities of mobile edge dislocations can be generated in the substrate metal at the film-substrate interface. These edge dislocations can move into the substrate and effect plasticity at the reduced flow stresses observed. In this investigation, additional use is made of surface modification (roughening) of the substrate surface to afford control over the density of potential dislocation sources at the film-substrate interface in coated materials. The results are described below.

It is well known that segregation of impurity elements at grain boundaries can facilitate intergranular fracture. However, it is not so widely recognised that segregation of major alloying elements in some materials, e.g. lithium and magnesium in aluminium alloys, may also be embrittling. Moreover, it appears that certain structural arrangements may be required in addition to segregation, and that ‘two-dimensional’ grain-boundary phase transitions are probably responsible for ductile-to-brittle fracture transitions with decreasing temperature (e.g. Hart [ 1 ], Lynch et al. [ 2 ]). For a given testing temperature, ductile-to-brittle fracture transitions may also occur with increasing ageing time due to increasing levels of segregation. Intergranular chemistry and structure can influence fracture resistance via effects on decohesion or dislocation emission from crack tips or via effects on slip transmission across boundaries, but the relative importance of these effects is not well established.

Dynamic photoelastic experimental method [ 1 , 2 ] and photoelastic experimental analysis for othotropic material [ 3 , 4 ] have been widely studied [ 1 , 2 ] since 1950. Photoelastic experimental method has been widely applied to the static and dynamic fracture mechaics [ 5 , 6 ] since 1970. During this time, R.J. Sanford [ 7 ] suggested the non-linear least square method using Newton-Raphson numerical method with Gaussian elimination method. We have used this method and this conception for determination of stress intencity factor using photoelastic experimental method [ 8 ]. The non-linear least square method have been applied to the photoelastic experimental hybrid method which can be used to obtain the static and dynamic stress intensity factor and stress concentration factor [ 9 , 10 , 11 ]. The Newton-Raphson numerical method with Gaussian elimination method have been used in the non-lineal least square method for the photoelastic experimental method. In this research, the photoelastic experimental hybrid method with Newtion-Raphson numerical method is called old technique. However, old technique is often diverged and unstable in high stress distribution as vicinity of crack tip.

Delamination in composite laminates is basically an interfacial crack between two orthotropic materials possibly oriented in different directions. One of the characteristics of interfacial cracks between two dissimilar materials is the oscillatory behavior of the stress field near the crack tip [ 1 ]–[ 2 ]. Classical fracture mechanics has been adopted for modeling delamination in composite materials; stress intensity factors are commonly used to characterize delamination fracture toughness. In using fracture mechanics with the stress intensity factors, one must make sure that the near tip singular stress field be dominant in the fracture process zone

This paper derives analytically the stress intensity factors (SIFs) of a frictional interfacial pennyshaped crack in a viscoleastic bimaterial subject to the action of a center of dilatation (see Fig. 1). This work is an extension of the 2-D problem considered by Chau and Wong [ 1 ].The standard linear viscoelastic solid or “three-parameter-viscoelastic-model” is adopted. Using the correspondence principle, the problem is formulated in Laplace transform space. The problem is decomposed into two Auxiliary Problems: (I) a bimaterial containing a center of dilatation; and (II) an interfacial crack in the bimaterial subject to tractions that cancel those induced by the Auxiliary Problem I. The elastic solution of Auxiliary Problem I has been given by Yu and Sanday through the use of Galerkin vector in 3-D space, which can easily be extended to that of a viscoelastic bimaterial subject to a sudden applied center of dilatation. Auxiliary Problem II can be solved by a Fourier transform technique proposed by Shifrin et al. [ 2 ] through the solution of a pseudodifferential equation subject to an arbitrary boundary traction condition. The applied traction from Auxiliary Problem I is first approximated by polynomials, and balancing coefficients yield a system simultaneous equations. The stress intensity factors can then be obtained. The approximate inverse of Laplace transform of Schapery is used to obtain the solutions in time. Creeping tests for the Swiss Central Alps shales have been adopted for viscoelastic parameter calibration. Frictional and overburden effects are also incorporated. For the limiting case of homogenous material, our solution agrees with the isotropic case [ 3 ]. When the number of terms needed for polynomials interpolation equal 15, the solutions converge to steady solution. In contrast to the 2-D cases, all mode I, II and III may appear.

Moisture-induced cracking during the solder reflow process is a critical reliability problem for plastic packages. Figure 1 shows the schematic diagram of a plastic ball grid array (PBGA) package with either a crack at the die attach or at the interface between solder mask and copper. These types of internal cracking are mainly resulted from a combination of thermal expansion mismatch of the package and the moisture-vaporized pressure acting on the crack surface inside the package. Such a phenomenon is known as the “popcorning” problem (Kuo et al. [ 1 ]).

There are many factors that influence at the mechanical behavior of gears. The gear’s mechanical phenomenons are greatly conditioned by teeth’s profile. One of the values that is most important and influential is the addendum modification coefficient value ( x _1, x _2).

Part-through cracks such as corner or surface cracks are one of the most common cracks in structural components. The paper focuses to develop analytic expresses for the stress intensity factor (SIF) for the surface crack in 3-D solid type structural components and crack growth. For this purpose three-dimensional finite-element analyses were used to develop an analytic equation for the stress-intensity factors. Traditionally, damages in structural components are assumed to have an elliptic shape that are loaded with cyclic loads and load spectra. Semi-elliptic surface cracks frequently initiate and grow in the vicinity of high stresses, stress concentrations, thermal stresses and other non-linear stress fields. Accurate stress intensity factors for such cracks are necessary for reliable prediction of fatigue crack growth rates or fracture. The slice synthesis approach used herein to computation of surface flaw stress intensities. To validate the analytic derived tress intensity facors for semi-elliptic surface cracks, finite element method is used. Three-dimensional finite elements were used to model a plate containing a semi-elliptic surface crack. The propagation of semi-elliptical surface initiated fatigue cracks has been considered. Analytic model for the stress intensity factors, derived in this work, are used for crack growth analyses and fatigue life predictions. Fatigue life under a load spectrum was predicted using these analytic stress intensity factors.. The finite element analyses were made using MSC/NASTRAN, with 20-noded isoparametric three-dimensional solid elements. In order to model the square root singularity at the crack tip, three-dimensional prism elements with four mid-side nodes at the quarter points (a degenerate cube with one face collapsed) were used and the separate crack tip nodal points were constrained to have the same displacements [ 1 ].

Based on theoretical preposition from reference Xiao et al . [ 1 ], concerning The subspace identification method as one of the possible variants of inverse dynamic analyses, behaviour of real structural systems with real load and really noise contaminated input/output data were investigated in this work.