The paper addresses the analytical determination of vibrodiagnostic parameters that describe the presence of normal-rupture
flat through-the-thickness and surface semi-elliptical central cracks in a rectangular homogeneous plate of constant thickness
for various plate fixing conditions and vibration modes. It is shown that the most sensitive vibrodiagnostic damage parameter
of a plate is the variation of the logarithmic decrement in the case of a through-the thickness crack and the second-harmonic
ratio of the vibration process in superharmonic resonance in the case of a surface crack.
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Translated from Problemy Prochnosti, No. 5, pp. 27–47, September–October, 2006. 相似文献
This paper develops a closed-form solution for anti-plane mechanical and in plane electric and magnetic fields in a magnetoelectroelastic
layer of finite thickness. Explicit expressions for the stresses, electric fields, and magnetic fields, together with their
intensity factors are obtained for the extreme cases for impermeable and permeable cracks. Solutions for some special cases,
such as a magnetoelectroelastic layer with infinite thickness, are also obtained. Applicability of the crack face electromagnetic
boundary conditions is discussed. It is found that the crack profile is important in obtaining the correct electromagnetic
fields and their intensity factors. The stress intensity factor, however, does not depend on the crack face electromagnetic
boundary condition assumptions. 相似文献
The paper focuses on debonding propagation along an interface, notably on the major influence of the interlocking between
the two faces of the debonding interface. The aim of the study is to obtain the data necessary for relevant and efficient
debonding modelling. The work associates experiment and simulation with the purpose of quantifying the interlocking along
the interface. The overlay material investigated was a fibre reinforced mortar (FRM). Direct tension tests of notched FRM
specimens were firstly conducted to obtain the tensile strength and the residual normal stress—crack width relationship. Its
Young's modulus was determined from compression tests. The substrate-overlay interface was investigated by direct tension
tests and flexure tests performed on composite substrate-overlay specimens. The direct tension tests provided the interface
tensile strength and the relationship between debonding-opening and residual normal tensile stress. Three point flexural static
tests informed on the structural behaviour of the interface. The debonding interface propagation was monitored using a video-microscope
with a maximum enlargement of ×175.
Using the identified and quantified parameters, modelling of the above mentioned static tests was carried out by the finite
elements method using CAST3M code developed in France by CEA (Centre for Atomic Energy). The comparison of modelling and experiment
results shows a good coherence and proves the important role of interlocking on the debonding mechanism. 相似文献
Technological advancements have led to an increase in demand for fabrication of small and cheap miniature components or parts, especially in the medical and electronic fields. In this research work, micro-rods of varying lengths and diameters were molded using a specially designed tabletop injection molding machine. The main purpose was to investigate whether complete filling of the microcavities was possible and whether small cavity openings will restrict melt flow into the cavities.
Process parameters, such as injection pressure, mold temperature and melt temperature were varied. The micro-rods obtained were analyzed with Scanning Electron Micrographs (SEM). The results showed that injection pressure was the most important parameter for microinjection molding. The use of a vacuum system also yielded better results. 相似文献
For composites to compete in vehicle suspension applications, it is essential to control their failure by utilising their strength in principal direction instead of shear. This can be achieved efficiently by employing a new configuration instead of existing one. This study marries between an elliptical configuration and the woven roving composites.
In this paper, the influence of ellipticity ratio on performance of woven roving wrapped composite elliptical springs has been investigated both experimentally and numerically. A series of experiments was conducted for composite elliptical springs with ellipticity ratios (a/b) ranging from one to two. Typical failure histories of their failure mechanism are presented and discussed. In general, this study demonstrated that composites elliptical spring can be used for light and heavy trucks and meet the requirements, together with substantial weight saving. The results showed that the ellipticity ratio significantly influenced the spring rate and failure loads. Composite elliptic spring with ellipticity ratios of a/b 2.0 displayed the highest spring rate. 相似文献
This paper describes elastic–plastic crack growth resistance simulation in a ceramic/metal functionally graded material (FGM)
under mode I loading conditions using cohesive zone and modified boundary layer (MBL) models. For this purpose, we first explore
the applicability of two existing, phenomenological cohesive zone models for FGMs. Based on these investigations, we propose
a new cohesive zone model. Then, we perform crack growth simulations for TiB/Ti FGM SE(B) and SE(T) specimens using the three
cohesive zone models mentioned above. The crack growth resistance of the FGM is characterized by the J-integral. These results show that the two existing cohesive zone models overestimate the actual J value, whereas the model proposed in the present study closely captures the actual fracture and crack growth behaviors of
the FGM. Finally, the cohesive zone models are employed in conjunction with the MBL model. The two existing cohesive zone
models fail to produce the desired K–T stress field for the MBL model. On the other hand, the proposed cohesive zone model yields the desired K–T stress field for the MBL model, and thus yields JR curves that match the ones obtained from the SE(B) and SE(T) specimens. These results verify the application of the MBL model
to simulate crack growth resistance in FGMs. 相似文献
We review, unify and extend work pertaining to evaluating mode mixity of interfacial fracture utilizing the virtual crack
closure technique (VCCT). From the VCCT, components of the strain energy release rate (SERR) are obtained using the forces
and displacements near the crack tip corresponding to the opening and sliding contributions. Unfortunately, these components
depend on the crack extension size, Δ, used in the VCCT. It follows that a mode mixity based upon these components also will
depend on the crack extension size. However, the components of the strain energy release rate can be used for determining
the complex stress intensity factors (SIFs) and the associated mode mixity. In this study, we show that several—seemingly
different—suggested methods presented in the literature used to obtain mode mixity based on the stress intensity factors are
indeed identical. We also present an alternative, simpler quadratic equation to this end. Moreover, a Δ-independent strain
energy release based mode mixity can be defined by introducing a “normalizing length parameter.” We show that when the reference
length (used for the SIF-based mode mixity) and the normalizing length (used for Δ-independent SERR-based mode mixity) are
equal, the two mode mixities are only shifted by a phase angle, depending on the bimaterial parameter ε. 相似文献
In this paper, the non-local theory solution of a Griffith crack in functionally graded piezoelectric materials under the anti-plane shear loading is obtained for the permeable electric boundary conditions, in which the material properties vary exponentially with coordinate parallel to the crack. The present problem can be solved by using the Fourier transform and the technique of dual integral equation, in which the unknown variable is the jump of displacement across the crack surfaces, not the dislocation density function. To solve the dual integral equations, the jump of the displacement across the crack surfaces is directly expanded in a series of Jacobi polynomials. From the solution of the present paper, it is found that no stress and electric displacement singularities are present near the crack tips. The stress fields are finite near the crack tips, thus allows us to use the maximum stress as a fracture criterion. The finite stresses and the electric displacements at the crack tips depend on the crack length, the functionally graded parameter and the lattice parameter of the materials, respectively. On the other hand, the angular variations of the strain energy density function are examined to associate their stationary value with locations of possible fracture initiation. 相似文献
Crack growth along an interface between two adjacent elastic–plastic materials in a layered solid is analysed, using special
interface elements to represent the fracture process ahead of the crack-tip. These interface elements account for ductile
failure by the nucleation and growth of voids to coalescence. In these elements the stress components normal to the interface
and the shear stresses are given by equilibrium with the surrounding material, and the stress component tangential to the
interface is determined by the requirement of compatibility with the surrounding material in the tangential direction. It
is assumed that the layers are sufficiently thick, so that the plastic regions around the crack-tip are much smaller than
the thickness of the nearest layers. The analyses focus on the effect of initial residual stresses in the layered material,
or on T-stress components induced during loading. The results show that the value of the T-stress component in the softer
material adjacent to the interface crack plays the dominant role, such that a negative value of this stress component gives
a significant increase of the interface fracture toughness. 相似文献