Papers by Keyword: Delamination Growth

Abstract: The delamination growth may occur in delaminated piezoelectric shell subjected to external load and it will further cause structural failure. Based on the variational principle of moving boundary and considering the contact effect between delamination regions, in this paper, the nonlinear governing equations for the delaminated piezoelectric shell under electro-thermo-mechanical loadings are derived, and the corresponding boundary and matching conditions are given. At the same time, according to the Griffith criterion, the formulas of energy release rate along the delamination front are obtained and the delamination growth is studied. In the numerical calculation, the energy release rate and delamination growth of axisymmetrical piezoelectric cylindrical shell are analyzed, and the effects of voltage, temperature and humidity, mechanical load, delamination length and depth on delamination growth are discussed.

Abstract: One of the most critical aspects of composite structures is indeed associated to delamination phenomenon, especially with reference to their fatigue behavior. As a matter of facts, delaminations are strongly influenced by the fatigue induced degradation phenomena which can lead to a significant increase of delaminated area with the number of cycles, reducing the structural load carrying capability. In the present paper, an advanced numerical approach, very similar to the Paris Law formulation and based on the Energy Release Rate, is presented. The proposed formulation, in the frame of a geometrical non-linear analysis, is able to take into account the local damage accumulation along the delamination front in order to evaluate the delamination growth under fatigue loading conditions. In order to test the effectiveness of the proposed numerical approach, the fatigue behavior of a delaminated panel with a central hole has been simulated and the obtained numerical results have been compared with literature experimental results.

Abstract: The present study involves an experimental and analytical investigation of the Mode II delamination propagation and the fibre bridging effects incorporated in the Fracture Process Zone (FPZ). End Notch Flexure (ENF) specimens from a unidirectional glass/epoxy composite material have been fabricated and tested. In order to construct the fracture resistance curve (R-curve) of the ENF tests, three different data reduction schemes have been utilized. The fibre bridging effects in the FPZ have been addressed with the use of traction-separation laws, as extracted from the corresponding calculated R-curves. These laws can be used to describe the constitutive relationship in interface finite elements, for the numerical modelling of delamination growth in laminated composite structures.

Abstract: Compression tests are conducted on composite laminates consisting of 16 unidirectional carbon/epoxy layers with two through-width delaminations. Two types of delamination length and location are considered. One is that a short delamination is located at the middle surface along the thickness direction and a long delamination is positioned between the second layer and the third layer. The other is that a long delamination is located at the middle surface and the position of the short elamination is between the second layer and the third layer. The results indicate that if the long delamination is close to the surface of the laminate, the inner, short delamination has no effect on the critical buckling stresses. However, the presence of inner, short delamination may significantly change the critical delamination growth stresses. If the short delamination is above the long delamination that is located on the middle surface, the presence of the short delamination may significantly reduce the critical buckling stresses. But its effects on the critical delamination growth stresses are minor.