1,721,074 research outputs found
DBEM and FEM analysis on non-linear multiple crack propagation in an aeronautic doubler-skin assembly
No full textThe performance of a riveted patch repair, applied on a cracked panel, is simulated by using both a commercially available Boundary Element code (BEASY) and a Finite Element code (ANSYS). A two-dimensional stress analysis on a single-sided repaired configuration is performed by both methodologies; consequently, the occurrence of out-of-plane bending and its effect on the through-thickness SIF (Stress Intensity Factor) variation is neglected. The connection between the two layers (patch and panel) is realised by 32 rivets, with through-cracks initiated on the most loaded holes. Special elements are used to model the crack: discontinuous elements in the DBEM (Dual Boundary Element Method) approach or quarter point elements in the FEM (Finite Element Method) approach. Different loading configurations are considered depending on the presence of a biaxial or uniaxial remote load and the non linear hole/rivet contact is simulated by gap elements. The most stressed skin holes are highlighted, and the effect of a through crack from such holes is analysed in terms of SIFs and stress redistribution. The accuracy in SIFs assessment by DBEM and FEM and the respective computational and pre-processing efforts are determined. Such a two-dimensional analysis allows us a straightforward pre-processing phase, and very short run times are needed. A peculiar arrangement of the pin configuration in the DBEM analysis allows us to take into account the real in-plane plate stiffness and the transversal pin stiffness, even in a 2D analysis (this is straightforward by using FEM)
Experimental and Analytical Investigation of the Shear Fracture Behavior of Bonded Joints
No full textThe demand of adhesive bonding as technique for the strengthening of existing structures is currently increasing in many engineering fields. Therefore, the prediction of bonded joints fracture behavior is an open issue for the structural safety of repairs. With this aim, a cohesive zone approach is adopted to determine the shear fracture behavior of epoxy resin interface layer of end notched flexure (ENF) specimen. Experimental tangential slip displacements of adherends are evaluated by digital image correlation (DIC) analysis. The identified traction-separation law can be implemented in a finite element (FE) code to predict the decohesion of adhesively bonded joints
Mode I Fracture Toughness Evaluation of Adhesively Bonded Joints via J-Integral and DIC
No full textAmorphous polymers, such as epoxy resins, are commonly used in the realization of adhesively bonded joints. In this paper an evaluation of mode I fracture toughness of bonded joints is presented. Moreover, an identification of cohesive zone model parameters via Rice's J-integral is described. Experimental tests are performed on double cantilever beam specimens and relative displacements between adherends are acquired by using the digital image correlation technique. The obtained interface law can be implemented in a finite element code for simulating the decohesion process of complex bonded structures
Stress Relaxation Behavior of Additively Manufactured Polylactic Acid (PLA)
Full text linkIn this work, the stress relaxation behavior of 3D printed PLA was experimentally investigated and analytically modeled. First, a quasi-static tensile characterization of additively manufactured samples was conducted by considering the effect of printing parameters like the material infill orientation and the outer wall presence. The effect of two thermal conditioning treatments on the material tensile properties was also investigated. Successively, stress relaxation tests were conducted, on both treated and unconditioned specimens, undergoing three different strains levels. Analytical predictive models of the viscous behavior of additive manufactured material were compared, highlighting and discussing the effects of considered printing parameters
Redesign of Structural Elements of Passenger Seat Based on Circular Economy Principles
Full text linkA product's environmental impact spans its entire lifecycle, from creation to disposal. The circular economy aims to eliminate this impact and resource waste by closing resource flow loops. In this perspective, circular design strategies are essential in achieving this goal. The end-of-life products should allow for easy material separation to enable reintegration into production cycles. In this work, design strategies that favor circularity, such as design for disassembly and design for recovery, were considered. The modular redesign of a passenger vehicle seat armrest was conducted with the purpose to achieve modularity, lightness, comfort improvement, easy maintenance, and reconfigurability of the armrest assembly. Finite element virtual tests were performed by using Ansys Workbench, in order to simulate, respectively, a loading condition according to NF F31-119 standard and an act of vandalism to separate the coupled parts of the new armrest. The results obtained in terms of strength and stiffness of the redesigned train seat armrest were considered satisfactory
Effect of fracture energy estimation on the predictions of mode II behavior of bonded joints using cohesive zone models
Full text linkFracture behavior of adhesive joints is an important topic in structural design of new structural elements or in retrofitting of existing ones. The mechanical models available in literature capable of predicting the failure mode of these junctions are mainly formulated within the cohesive zone model (CZM). Direct approaches for identification of CZM parameters in pure mode II of bonded joints, based on different modelling of strain energy release rate (SERR), are presented. The mode II SERR was determined from experimental results on end notched flexure (ENF) tests. Digital image correlation (DIC) analysis was used to evaluate the shear slip displacements of adhesive layer. The mode II cohesive traction-separation law was identified by numerical differentiation of SERR and best fit equation systems were adopted for an analytical description of cohesive interface behavior. Moreover, the obtained CZM laws were used for predicting the decohesion process by finite element analyses. Global and local responses of ENF test were compared with experimental data in terms of load-displacement and adhesive tangential displacement-time curves, respectively. A more accurate modelling of fracture energy resulted in a sounder agreement of prediction with experimental dat
Evaluation of energy release rate for delamination defects at the skin/stringer interface of a stiffened composite panel
No full textThis paper deals with numerical investigation on a stiffened composite panel under longitudinal compression load, in presence of artificial delamination defects between skin/stringer interface layers.
At first, both the experimental and numerical non-linear equilibrium paths were determined, until the failure load value of the structure was reached. Then local evaluation of the energy release rate parameter was performed at defect front, by means of a hybrid (FEM/analytical) procedure based on a particularized virtual crack closure technique. The same FE shell model was used to perform both global and local calculations by means of a single analysis
- …
