1,721,095 research outputs found
Torsion shear strength of ceramics joined by brittle or ductile materials
No full textAssessing the shear strength of a joined ceramic or CMC is an essential task in components design. Indeed, what is needed for design purposes, is the true shear strength, while several standard tests only give conventional values, disregarding multiaxiality and non-uniformity of the actual stress distribution. If used under proper conditions, torsion test has the advantage of producing a state of pure shear stress with a known distribution in the joint section. A distinction must be done whether the joining material is brittle or ductile. In case of brittle behavior, the stress concentration factor due to the specimen geometry must be taken into account; moreover, since the stress state is intrinsically biaxial, failure may occur out of the joint section. In case of ductile behavior, the non-linear effect of plasticity must be included. The talk discusses these aspects and proposes a procedure suitable to assess the pure shear strength of joined ceramics
Failure Criteria for Adhesive Bonds and their Relevance to Design: A Review
No full textA unique, generally accepted, methodology to predict the failure conditions and load of adhesive bonds is still lacking. The primary distinction that needs to be done is between: i) rupture conditions, which inevitably involve material non-linearity; ii) design conditions, within linearity limits. Typically, the research is focussed on i), and this excludes the numerous solutions or numerical models based on linear elasticity. A first research line on bond failure relies on adhesive plasticity. Hart-Smith [1] obtained design charts admitting that at the ends of the overlap the adhesive yields plastically. Later, Crocombe and co-authors [2] assumed global yielding of the adhesive to be the key phenomenon. A second research line, appeared since early 1970‘s [3], is based on fracture mechanics; the related tests are focussed on the adhesive strength by using ad hoc specimens (double cantilever beam, end notched flexure). In a design perspective, the problem in applying fracture mechanics is that the existence of a crack must be assumed somehow. A synthesis of these two approaches, likely the most popular today, is given by damage mechanics, in particular by the cohesive zone used to describe the failure of the adhesive [4]. Clearly, all these methodologies require numerical modelling. On the other hand, in a simpler perspective oriented to joint design, criteria based on adhesive elastic stresses have been also proposed [5], to help dimensioning the joints. These are based on conventional stresses, for which a limit combination can be easily assessed experimentally, under both static and dynamic (impact) conditions. The proposed presentation aims at giving an overview of the available approaches, trying to identify merits, lacks and needs for future developments. [1] L.J. Hart-Smith, Tech. Rep. CR-112235,112236 (1973). [2] A.D. Crocombe, Int. J. Adhes. Adhes., 9, 145 (1989). [3] E.J. Ripling, S. Mostovoy, H.T. Corten., J. Adhesion, 3, 107 (1971). [4] J.W. Hutchinson, A.G. Evans, Acta Mater., 48, 125 (2000). [5] L. Goglio, M. Rossetto, E. Dragoni, Int. J. Adhes. Adhes., 28, 427 (2008
Chapter 5. Continuum Mechanics Modelling by Finite Elements
No full textThe chapter reports in brief the principles and several cases of application of the FEM to the analysis of bonded joints. The topics are presented under the light of selected papers of the related scientific literature. The main topics treated are failure prediction based on continuum analysis, model size reduction (efficient modelling), stress singularities and geometric non-linearity
Static lateral compression of aluminium tubes: strain gauge measurements and discussion of theoretical models
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Comparison of fatigue data using the maximum likelihood method
No full textThe paper describes procedures to compare the fatigue behaviour of two populations corresponding to batches that differ for a factor on the basis of fatigue data of two samples. Fatigue data are elaborated by means of the maximum likelihood method to obtain the SNP curves and their confidence intervals. The likelihood ratio test is used to identify the most adequate distribution and model. To analyse the influence of the factor, two integrated procedures are adopted: the first one is based on the LR test, the second is an empirical procedure, based on the comparison of the confidence intervals of the curves
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