1,721,052 research outputs found
A coupled cohesive zone model for transient analysis of thermoelastic interface debonding
No full textA coupled cohesive zone model based on an analogy between fracture and contact mechanics is proposed to investigate debonding phenomena at imperfect interfaces due to thermomechanical loading and thermal fields in bodies with cohesive cracks. Traction-displacement and heat flux–temperature relations are theoretically derived and numerically implemented in the finite element method. In the proposed formulation, the interface conductivity is a function of the normal gap, generalizing the Kapitza constant resistance model to partial decohesion effects. The case of a centered interface in a bimaterial component subjected to thermal loads is used as a test problem. The analysis focuses on the time evolution of the displacement and temperature fields during the transient regime before debonding, an issue not yet investigated in the literature. The solution of the nonlinear numerical problem is gained via an implicit scheme both in space and in time. The proposed model is finally applied to a case study in photovoltaics where the evolution of the thermoelastic fields inside a defective solar cell is predicted
Numerical modelling of microcracking in PV modules induced by thermo-mechanical loads
Full text linkAbstract Micro-cracking in polycrystalline Silicon is a serious concern for the durability of photovoltaic (PV) modules due to the resulting electrical power-loss. In this contribution, a thermo-mechanical cohesive zone model is proposed to predict the evolution of micro-cracks under the action of mechanical and thermal loads. The classical nonlinear cohesive zone approach, used in fracture mechanics to depict the phenomenon of cracking as a result of progressive breakage of atomic bonds, is extended to thermo-elastic fields. The additional thermal resistance of micro-cracks due to imperfect bonding is estimated according to an analogy with a contact mechanics formulation, where the dependency on the crack opening is suitably accounted for. A numerical example shows the applicability of the proposed approach to practical problems
Free vibration analysis of a von Koch Beam
No full textAbstractIn this paper, the free undamped motion of a cantilever von Koch beam is investigated. The reduction of the stiffness and mass matrices leads to simple analytical recursive relationships depending on the fractal dimension of the structure. Results are then extended to perform a detailed modal analysis, which suggests peculiar scaling laws for the natural frequencies and modal shapes of the structure. Energy considerations are also provided. Finally, the potentiality of the von Koch beam as a fractal antenna is examined in terms of resonant frequencies
Analytical Stress Intensity Factors for cracks at blunted V-notches
Full text linkAbstractAn analytical expression for the Stress Intensity Factor (SIF) related to a crack emanating from a blunted V-notch root is put forward. Different notch amplitudes, ranging from 0° to 180°, and different crack length to root radius ratios, ranging from 0 to 10, are taken into account. The analysis is limited to mode I loading conditions, as long as the crack length is sufficiently small with respect to the notch depth. The proposed formula improves significantly the predictions of the relationships available in the Literature, by considering a notch amplitude dependent parameter: its values are estimated through a finite element analysis (FEA)
An Accurate Thermoviscoelastic Rheological Model for Ethylene Vinyl Acetate Based on Fractional Calculus
Full text linkThe thermoviscoelastic rheological properties of ethylene vinyl acetate (EVA) used to embed solar cells have to be accurately described to assess the deformation and the stress state of photovoltaic (PV) modules and their durability. In the present work, considering the stress as dependent on a noninteger derivative of the strain, a two-parameter model is proposed to approximate the power-law relation between the relaxation modulus and time for a given temperature level. Experimental validation with EVA uniaxial relaxation data at different constant temperatures proves the great advantage of the proposed approach over classical rheological models based on exponential solutions
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