1,354,348 research outputs found
Improvement of a cohesive zone model for fatigue delamination rate simulation
No full textThe cohesive zone model (CZM) has found wide acceptance as a tool for the simulation of delamination in composites and debonding in bonded joints and various implementations of the cohesive zone model dedicated to fatigue problems have been proposed in the past decade. In previous works, the authors have developed a model based on cohesive zone to simulate the propagation of fatigue defects where damage acts on cohesive stiffness, with an initial (undamaged) stiffness representative of that of the entire thickness of an adhesive layer. In the case of a stiffness that is order of magnitude higher than the previous one (for instance, in the simulation of the plyto- ply interface in composites), the model prediction becomes inaccurate. In this work, a new formulation of the model that overcomes this limitation is developed. Finite element simulations have been conducted on a mode I, constant bending (constant G)-loaded double cantilever beam (DCB) joint to assess the response of the new model with respect to the original one for varying initial stiffness K0 and cohesive strength σ0. The results showed that the modified model is robust with respect to changes of two orders of magnitude in initial stiffness and of a factor of two in σ0
Microstructural, multilevel simulation of notch effect in ferritic ductile cast iron under low cycle fatigue
Full text linkTriaxiality of stress affects damage and failure of ductile metals. In mechanical components, triaxiality increases in the proximity of a notch, or, at the microstructural level, due to inclusions or voids. In this work, the effect of triaxiality on the LCF of ductile cast iron is investigated by a multilevel approach, homogenizing the response of a microstructural model which feeds a notched specimen. Moving from micro- to macro-scale, results indicate that triaxiality shorten the fatigue life. Thus, the notch effect on fatigue life of cast iron can be explained in terms of the combined effects of microstructure and applied triaxiality
Erratum to: A procedure for the simulation of fatigue crack growth in adhesively bonded joints based on the cohesive zone model and different mixed-mode propagation criteria
No full textDEVELOPMENT OF A WORKFLOW FOR THE VIRTUAL OPTIMIZATION OF A NANOFIBER-INTERLEAVED COMPOSITE LAMINATE SUBJECTED TO IMPACT LOADING
Full text linkDelamination is one of most common failure mechanisms for composite materials. By interleaving nanofibers between laminate plies, the authors showed that it is possible to control the interlaminar fracture toughness. In particular, either a toughening or an embrittlement of the interface could be obtained by varying fibre diameter, fiber arrangement (random, aligned) and mat thickness. The modification induced by the nanomat can be therefore exploited in order to tailor the delamination strength of the laminate. The aim of this work is to identify a way to optimize the impact strength of a composite laminate with interleaved nanomats with respect to the maximization of the energy dissipated by delamination under impact. Impact damage is simulated using the Finite Element Method (FEM) with the Abaqus software. Cohesive elements are placed at the interfaces between groups of plies with different orientation of a plain weave composite laminate. Each interface can be assigned three different cohesive properties. The cohesive zone properties of virgin and nanomodified interfaces were identified in a previous work. The optimization workflow took into account also the possibility of changing the initial ply orientation. A multiobjective optimization was run for the counteracting objectives of max damage-dissipated energy and minimum decrease of composite stiffness
Assessment of load ratio effect on fatigue crack growth using partial crack closure
No full textAccording to a damage-tolerant approach, fatigue life becomes virtually infinite if the ΔK due to service loads is lower than the threshold for fatigue crack growth (FCG). For this motivation, a proper evaluation of ΔKth is very important. On the other hand, for a given material this parameter appears to be strongly influenced by material microstructure and R=Kmin/Kmax ratio. At high propagation velocity this influence is explained by classical closure concept introduced by Elber, but this approach does not always work at threshold. Recently, new methods to account for microstructure and R-ratio effects at low propagation rates were proposed. The aim of this work is to evaluate the effectiveness of those methods testing very different materials: (i) a case hardened steel and (ii) an aluminium matrix particulate composite
Hybrid joints: Evaluation of the increase of the mechanical performances with respect to simple joints
No full textHybrid joints allow to bring together the advantages of bonded joints (i.e. lightweight design, cost reduction and higher energy absorption in case of impact loading) with the confidence, the high specific strength and well know production process of traditional mechanical joining technologies like welding, riveting and clinching. In this way, higher performances in terms of strength, stiffness and energy absorption are achieved with respect to simple adhesive, welded or fastened joints, while costs can be reduced with respect to welding or fastening and the manufacturing process is facilitated with respect to adhesive bonding. Many works deal with the static [1-4] and fatigue [5, 6] characterization of hybrid joints, and they point out higher mechanical properties in comparison with simple joints. The reason is found in a synergistic effect of the joining techniques [7] and in a more favourable stress distribution [8, 9]. In this work an extensive experimental campaign was carried out in order to compare the strength of weld-bonded, clinch-bonded and rivet-bonded joints with that of the related non-hybrid joints, evaluating also the influence of geometrical and environmental factors. The experimental analysis was conducted using the Design of Experiments (DoE) methodology, taking the maximum load (F max), the stiffness (K) and the energy absorption prior to the failure (E n) as objectives
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