1,721,041 research outputs found
Design of a prototipe of servo hydraulic multiaxial testing machine for specimens, structural elements and structures
No full textA fracture toughness identification method for the debonding test of DCB specimens accounting for three-dimensional effects
Full text linkThe fracture toughness of adhesive joints and laminated composites subjected to opening load is commonly evaluated using Double Cantilever Beam (DCB) specimens according to ISO or ASTM standards. The formulations of these standards are based on two-dimensional (2D) elastic beam models, although a three-dimensional (3D) effect, related to the curvature of the crack front in DCB specimens and affecting the measured fracture toughness, is present and reported in literature. In this paper, a novel test set up is proposed to evaluate the energy release rate by revisiting a recently published decohesion model that implicitly considers the presence of 3D effects, without measuring the crack propagation length. The elastic behaviour of adherends in terms of Young's modulus and only load and macroscopic angular displacements response are necessary. Using the finite element code Ansys APDL, several decohesion test simulations of 3D DCB specimen models were performed. The fracture surfaces were modelled using cohesive elements and the adherends as isotropic material. The results obtained from the simulations were used to evaluate the accuracy of the fracture toughness obtained both through the active standards and via the novel approach, by comparison with that imposed in the cohesive law. The results showed that the standardized data reduction schemes were affected by systematic errors up to 30%, whilst the proposed methodology gave a negligible error in the fracture toughness evaluation compared to that imposed in the cohesive law
Stability of cruciform specimens for fracture tests under compression
No full textCruciform specimens have been developed in the last decades in order to evaluate the fatigue and fracture material behaviour under biaxial stress fields. These evaluations have been generally conducted under positive load ratios, so as to prevent the potential buckling of these generally thin specimens. This paper reports a numerical investigation on the stability of two cruciform specimens in order to provide useful information for the design of biaxial fracture tests under both tension and compression. Two cruciform geometries were selected among those widely accepted in literature and slightly modified so as to apply equal boundary conditions. FEM simulations were performed under tensile and compressive loading conditions by considering geometric imperfections based on the superposition of the buckling modes. Results were cross-compared in terms of stress fields, load–displacement curves, stress intensity factors and critical loads along crack propagation. Guidelines of general validity were derived
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
Numerical and Experimental Investigation on the Influence of Tightening in a Hybrid Single Lap Joint
No full textHybrid mechanical joints are achieved by the simultaneous use of multiple connection mechanisms such as bolting and bonding. This technique allows to obtain advantages in terms of mechanical properties compared to simple joints such as longer fatigue life and operability in critical environmental conditions. Many parameters influence the structural behavior of the hybrid junctions in this perspective numerical simulation can play a decisive role to the cause. Using hybrid joints allows generally to obtain a more homogeneous stress distribution than bolted ones which is why, over the years, such type of joint is widely used in the automotive and naval industries as well as in the avionics, with particular reference to the residual strength in partially damaged components. In the present work, a numerical model representative of tensile tests on single lap joints characterized by adherends of different nature is presented
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Robust design of a polygonal shaft-hub coupling
Full text linkIn this work, the Taguchi method is applied for the optimal choice of design parameter values for a
polygonal shaft-hub coupling. The objective is to maximize a performance function, minimizing, at the same
time, its sensitivity to noises factors (robust design). The Design of Experiments (DoE) is adopted to set up a
plan of numerical experiments, whose different configurations are simulated using the Boundary Element
Method (BEM)
From test data to FE code: A straightforward strategy for modelling the structural bonding interface
Full text linkA straightforward methodology for modelling the cohesive zone (CZM) of an adhesively bonded joint is developed, by using a commercial finite element code and experimental outcomes from standard fracture tests, without defining a damage law explicitly. The in-house developed algorithm implements a linear interpolated cohesive relationship, obtained from literature data, and calculates the damage at each step increment. The algorithm is applicable both to dominant mode I or dominant mode II debonding simulations. The hypothesis of unloading stages occurrence is also considered employing an irreversible behaviour with elastic damaged reloading. A case study for validation is presented, implementing the algorithm in the commercial finite element method (FEM) software Abaqus®. Numerical simulation of dominant mode I fracture loading provides with satisfactory results
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