Constitutive Modelling And Failure Prediction For Silicone Adhesives In Fa Ade Design
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Constitutive Modelling Of Structural Adhesives Experimental And Numerical Aspects
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Author :
language : en
Publisher:
Release Date : 2010
Constitutive Modelling Of Structural Adhesives Experimental And Numerical Aspects written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
Structural adhesives are recognized by the industry as a powerful alternative solution to traditional fastening methods such as welding or riveting. As a new technological solution, they introduce requirements in terms of the evaluation of their mechanical performances. In particular, enhanced safety guarantee requires not only to know the material performance in standard laboratory tests but to be able to predict it under real conditions, for complex shaped parts. This may be done by finite element simulation. Nevertheless, the small thickness and the specific material behaviour of the adhesive bonded joint make modelling difficult using available numerical tools. This Ph-D work focuses on the assessment of structural adhesive joints bonded with the structural adhesive SikaPower-490 using finite element analysis. Both strength and damage aspects are evaluated under quasi-static loadings. First, experimental tests required to measure the mechanical properties of structural adhesives are investigated. The former group of experiments is devoted to the assessment of the elastoplastic behaviour of the adhesive up to its maximal strength and for different loading paths. The experiments consist of butt-bonded hollow cylinders, classical and modified Thick Adherend Shear Tests, and modified Arcan specimens. The latter group of experiments composed of Double Cantilever Beam and End Notched Flexure specimens is devoted to the study of the damage and fracture behaviour of the adhesive. Second, material constitutive models for the finite element simulation of structural adhesives are investigated. Standard constitutive models such as von Mises and Exponent Drucker-Prager model are reviewed, but their lack of accuracy lead to the implementation of a pressure-dependent constitutive model inspired from Mahnken and Shlimmer. The identification of material constitutive parameters is an important step: The non-homogeneity of stresses in the adhesive layer requires the implementation of a specific inverse identification procedure. Using this method, a set of material parameters can be identified which describes nicely the non linear behaviour of the adhesive under multi-axial loadings. In order to meet requirements of the automotive industry in terms of modelling and computation time, the constitutive model developed so far with solid elements is validated using interface elements. For the study of quasi-static damage and failure in the adhesive layer, a constitutive traction-separation elasticdamage model is tested with interface elements. The advantages and drawbacks of the two elastoplastic and damage constitutive models are compared and the extension of the elastoplastic model to take damage and fracture into account is considered. Third, the constitutive models investigated so far are validated for the finite element simulation of industrial case studies representative of bonded parts in a car's body in white. A T-joint submitted to two different loading and a closed hat profile bonded to a plate and submitted to flexion loading configurations are simulated.
Electrical Thermomechanical And Reliability Modeling Of Electrically Conductive Adhesives
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Author : Bin Su
language : en
Publisher:
Release Date : 2006
Electrical Thermomechanical And Reliability Modeling Of Electrically Conductive Adhesives written by Bin Su and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with Adhesives categories.
The first part of the dissertation focuses on understanding and modeling the conduction mechanism of conductive adhesives. The contact resistance is measured between silver rods with different coating materials, and the relationship between tunnel resistivity and contact pressure is obtained based on the experimental results. Three dimensional microstructure models and resistor networks are built to simulate electrical conduction in conductive adhesives. The bulk resistivity of conductive adhesives is calculated from the computer-simulated model. The effects of the geometric properties of filler particles, such as size, shape and distribution, on electrical conductivity are studied by the method of factorial design. The second part of the dissertation evaluates the reliability and investigates the failure mechanism of conductive adhesives subjected to fatigue loading, moisture conditioning and drop impacts. In fatigue tests it is found that electrical conduction failure occurs prior to mechanical failure. The experimental data show that electrical fatigue life can be described well by the power law equation. The electrical failure of conductive adhesives in fatigue is due to the impaired epoxy-silver interfacial adhesion. Moisture uptake in conductive adhesives is measured after moisture conditioning and moisture recovery. The fatigue life of conductive adhesives is significantly shortened after moisture conditioning and moisture recovery. The moisture accelerates the debonding of silver flakes from epoxy resin, which results in a reduced fatigue life. Drop tests are performed on test vehicles with conductive adhesive joints. The electrical conduction failure happens at the same time as joint breakage. The drop failure life is found to be correlated with the strain energy caused by the drop impact, and a power law life model is proposed for drop tests. The fracture is found to be interfacial between the conductive adhesive joints and components/substrates. This research provides a comprehensive understanding of the conduction mechanism of conductive adhesives. The computer-simulated modeling approach presents a useful design tool for the conductive adhesive industry. The reliability tests and proposed failure mechanisms are helpful to prevent failure of conductive adhesives in electronic packages. Moreover, the fatigue and impact life models provide tools in product design and failure prediction of conductive adhesives.