Three-dimensional elastic deformation of functionally graded isotropic plates under point loading

Acknowledgement Financial support of this research by The Royal Society (UK) under grant number JP090633 is gratefully acknowledged.Peer reviewedPostprin

Delamination growth in buckled composite struts

Existing analytical models dealing with buckling and postbuckling phenomena of delaminated composites comprise one limitation: the restriction to stationary delaminations. In the current work, an analytical framework is presented which allows to model the postbuckling response of composites without such limitation. Therefore, the well-known problem of a composite strut with a through-the-width delamination is studied. The system is fully described by a set of I generalized coordinates. The postbuckling response for a stationary delamination is modelled using the conventional total potential energy approach. The postbuckling response for a non-stationary delamination, i.e. once delamination growth occurs, is modelled using an extended total potential energy functional in which the delamination length is expressed by the generalized coordinates and the load parameters. By solving the underlying variational principle the postbuckling response is obtained. Implementing the Rayleigh–Ritz method yields a set of non-linear algebraic equations which is solved numerically. Postbuckling responses for a cross-ply laminate are provided until the strut fails. Depending on delamination depth and length additional load bearing capacities of such composite struts are documented before failure due to unstable delamination growth occurs

Delamination buckling in composite plates: an analytical approach to predict delamination growth

An analytical modelling approach is presented which is capable of determining the post-buckling responses as well as the onset of delamination growth of multi-layered composite plates with an embedded circular delamination. In order to overcome current drawbacks of analytical models regarding embedded delaminations, the model employs a problem description in cylindrical coordinates and a novel geometric representation of delamination growth in conjunction with a Rayleigh-Ritz formulation and the so-called crack-tip element analysis. The modelling approach is applied to study the compressive response of composite plates with thin-film delaminations loaded under radial compressive strain. Post-buckling responses and the onset of delamination growth are determined for several layups. The results are in very good agreement with finite element simulations while requiring low computational cost

Experimental and numerical investigation on pre-stressed lattice structures

The effect of pre-stress on the buckling behaviour of geometric unit cells of collinear square lattices is investigated experimentally and numerically. The geometric unit cells are manufactured using fused deposition modelling. Manufacturing strategies are presented which incorporate fibres subjected to pre-stress within the unit cell. The effect of pre-stressed fibres is analysed by comparing the compressive behaviour of unit cells with and without fibre reinforcement. The buckling behaviour of the unit cells is also investigated numerically by employing a parametric study within Abaqus varying the pre-stress in the fibres. The experimental test series shows that the addition of pre-stressed fibres to the system results in an increase in buckling and maximum load of 260%–480% and 220%–350% respectively. The increase strongly relates to the manufacturing quality, i.e. the bonding between the lattice material and the fibres, where a sufficient bonding yields significantly larger loads. The experimental findings on the qualitative and quantitative buckling behaviour correspond well with results obtain from the numerical study

Overload effects on a ferritic-baintic steel and a cast aluminium alloy: two very different behaviours

Load controlled fatigue tests were performed up to 107 cycles on flat notched specimens (Kt =2.5) under constant amplitude and variable amplitude loadings with and without periodical overloads. Two materials are studied: a ferritic-bainitic steel and a cast aluminium alloy. These materials have a very different cyclic behaviour: the steel exhibits cyclic strain oftening whereas the Al alloy shows cyclic strain hardening. The fatigue tests show that, for the steel, periodical overload applications reduce significantly the fatigue life for fully reversed load ratio (Rr = – 1), while they have no influence under pulsating loading (Rr = 0). For the Al alloy over-loads have an effect (fatigue life decreasing) only for variable amplitude loadings. The detrimental effect of overloads on the steel is due to ratcheting at the notch root which evolution is overload's dependent