Catálogo de publicaciones - libros

Damage accumulation in laminated composite is a major concern in the design and use of composite structures. Accumulated damage can affect laminated response and ultimate strength, which are critical to design of load-carrying structural components. For the optimal design of composite structures, laminate response beyond the point of initial matrix cracking must be known, and subsequent damage and failure modes induced by accumulated matrix crack must be understood.

Recently Shodja and Kamali [ 1 ], and Kamali and Shodja [ 2 ], introduced a 3D semi-analytical approach for determination of the electro-mechanical fields of piezoelectric solids with material singular surfaces. The proposed methodology is particularly effective for problems involving external and internal boundaries with complex geometries, which have closed form expressions, and not necessarily in the form of polynomials. The previous formulations are devoted to material singular surfaces with perfect bonding. Due to the promising features of the formulation, the authors have continued to study various capabilities as well as convergence rate and accuracy of the approach. The present work extends the formulation to solids in which the material discontinuity surfaces may have one of the following six conditions: (1) perfect bonding; (2) pure debonding; (3) in-plane pure sliding; (4) out-of-plane pure sliding; (5) full debonding; or (6) partial debonding. Moreover, the interface is electroded in the sense that the interface is subjected to an arbitrary electric potential function, Φ = f(x, y). One of the advantages of the proposed method is that all of the above-mentioned cases are treated in a unified manner.

Ceramics have many important applications one of them being in gas turbine engines, where they operate under high temperatures (about 1300 °C). The mechanical behavior of ceramic materials under high temperature is complex with the following main characteristics: nonlinear rate-dependent behavior and asymmetric behavior in tension and compression.

A numerical study of growing elliptical cracks in a unit cube is undertaken with the help of an FEM simulation.

The effect of microstructure as a consequence of precipitation aging on the fracture behavior, deformation mechanisms, mechanical properties, and microstructures of aluminum-lithium was studied. The alloy studied was an aluminum-lithium-zirconium alloy. The precipitation response with aging time and temperature was studies in order to correlate the deformation response to the alloys to the heat treating, microstructure, and fracture surface characteristics and features. The primary focus of this study was to relate the variation in ductility with aging to the microstructural parameters and fracture mechanisms. An aluminum alloy containing 2.6wt.%Li and 0.09wt.% Zr exhibited very low tensile ductility consistently prior to the peak-aged strength independent of thermal treatment. A transition was characterized by very low ductility in the slightly underaged condition up to the near peak-aged condition, then followed by a substantial increase in ductility with aging after the peak-aged treatment. Based on the quantitative microscopy of the size of the precipitates, it was proposed that the increase in the ductility of the alloy after aging was a consequence of particle coarsening with aging and resulting in Orowan looping due to the transition from dislocation particle shearing to dislocation particle bypassing with increasing precipitate size. As the interparticle spacing increased with overaging, and the dislocations were impeded by and thus bypassed the larger particles, the amount of plastic deformation increased as was reflected by the strength and ductility experimental data.

The paper is dedicated to the development of methods for solving one-dimensional singular and hypersingular integro-differential equations with generalized Cauchy kernels. Using the means of the theory of special functions, constructive methods of direct (without regularization) numerical solution of such equations are suggested. One-dimensional singular integro-differential equation (SIDE) with standardized integration interval in sufficiently general case is considered: (1) $$ \begin{gathered} A\phi '(\eta ) + B\phi (\eta ) + C\int\limits_{ - 1}^1 {\frac{{\phi '(\xi )d\xi }} {{\xi - \eta }}} + D\int\limits_{ - 1}^1 {\frac{{\phi '(\xi )d\xi }} {{\xi - \eta }}} + \int\limits_{ - 1}^1 {K(\xi ,\eta )} \phi '(\xi )d\xi + \hfill \\ + \int\limits_{ - 1}^1 {L(\xi ,\eta )} \phi (\xi )d\xi = p(\eta ),{\text{ }} - 1 < \eta < 1,{\text{ }}\phi '{\text{(}}x{\text{) = }}\frac{{d\phi (x)}} {{dx}} \hfill \\ \end{gathered} $$ Here φ ( ξ ) is unknown function, p ( η ) is bounded continuous function known on the interval [−1, 1], and kernels K ( ξ, η ) and L ( ξ, η ) can have “fixed” singularities on the end points of integration interval, i.e. becomes unbounded only if ξ and η approach simultaneously to one of end point of the interval[−1, 1] ( ξ = η → ± 1 ). In the latter it is assumed, that K ( ξ, η ) and L ( ξ, η ) are generalized Cauchy kernels, i.e. their singularities have form ρ ^−1 ( ρ → 0) (Erdogan et al . [ 1 ]). A, B, C , and D are constants, which may be functions of η under certain assumptions (see Muskhelishvili [ 2 ]). Constants and functions K ( ξ, η ), L ( ξ, η ) and p(η) and are real or complex

.Life assessment of aircraft or aerospace fracture critical parts, through the linear elastic fracture mechanics approach, needs to have fatigue crack growth rate (FCGR) data for the material under consideration. These tests are costly and time consuming. In many cases, the time required to complete the standard FCGR test exceeds the deadline set forth by the customers. In other cases, due to the budget constraint, the analyst is forced to select a similar material, which in many cases life estimation results can be too conservative or incorrect. The proposed method is capable of generating the regions I, II, and III of the FCGR curve without conducting the ASTM-E647 testing standards. The ASTM FCGR tests include machining the C(T) or M(T) specimens, pre-fatiguing, measuring crack growth, gathering data, and interpreting of the data. Moreover, in region I of the FCGR, the load shedding technique is commonly used to capture the threshold stress intensity factor, which can be tedious and time consuming. The proposed analytical method can independently estimate each region of the curve. These regions will also be connected to establish the total FCGR curve through the well known fatigue crack growth rate equation established by Forman and Newman [ 1 ]. The final failure in the accelerated region (region III), where Δ K≈Kc , can be estimated through the Griffith energy balance equation by using the full stress-strain curve, established from a reliable source, for the material [ 2 ]. The Paris region can be established by selecting two points on the curve (the two points are both situated before the threshold and accelerated regions, where Δ K th<Δ K < Kc ). For these two points, the ratio of Δ K / Δ K th and Δ K / Kc were found to be a constant for many metallic alloys. The threshold values for Aluminium and Titanium alloys were found to be related to the material plane strain fracture toughness, KIc (Figure 1), and were falling between the KIc/4π and KIc/3π as shown in Figures 2a & b for the 2000 series aluminums, respectively.

The numerical analysis of ductile damage and failure in engineering materials and metal matrix composites is often based on a micromechanical description of the damage and failure process (Gurson [ 1 ], Needleman and Tveergard [ 2 ], Tveergard and Needleman [ 3 ]). In heterogeneous metal matrix composites, ductile crack extension occurs only in the ductile metallic phase, whereas cracks of rigid inclusions and decohesion is not necessarily experimentally observed.

A hybrid boundary element method (BEM) for transient problems in elastodynamics is developed here [ 1 ] as a means for investigating ground motion phenomena in geological regions with complex geometry, variable material properties and in the presence of both interface and internal cracks. Two different aspects of the problem are considered, namely computation of (a) ground motions in the form of synthetic seismograms that are manifested at the free surface of the geological region as it is swept by a seismically-induced pressure wave and (b) evaluation of the near crack-tip stress concentration field (SCF) that develops around cracks buried within the deposit for the same type of loading. The present method combines both displacement and regularized traction BEM in the Laplace transformed domain [ 2 ] for the crack-free and cracked states, respectively, while the transient nature of the wave scattering phenomenon is reconstructed through use of the numerical inverse Laplace transformation. Furthermore, plane strain conditions are assumed to hold and the response of the geological region remains within the linear elastic range. The basic strategy, whereby the aforementioned two states are superimposed, has been successfully used in the past for problems in fracture mechanics. Following numerical implementation of the hybrid BEM, validation-type examples serve to calibrate the methodology. Finally, the method is used for solving the seismic response of a complex geological region so as to reach some conclusions regarding the relative influence of various key parameters of the problem (such as layering, surface canyon, crack interaction, etc.) on the scattered displacement field and on the SCF. Further extension of the method to cover mildly inhomogeneous continua is also planned [ 3 ].

An engineering problem is considered in which an axisymmetric crack initiates from the inside of a piston crown due to both thermal and mechanical load from the combustion as shown in Fig.1. To study the crack propagation the boundary element method is well suited because discretization only occurs at the boundary.