Search results for "fracture mechanic"
showing 10 items of 108 documents
Slow crack propagation in polyethylene: determination and prediction
1991
Abstract A model is developed connecting the stress intensity factor KI with the propagation rate d h d t of slow cracks. The model is based on the concept of the chain relaxation capability. Experimental KIversus d h d t data are reported for polyethylenes of varying molecular mass M, density ϱ, initial notch length h0 and at different stress levels σ. Predictions of the theory concerning the effect of each of these parameters on crack propagation are confirmed by the experimental results. In particular, the equation for KI as a function of d h d t does not contain h0 nor σ. Experimental plots of KIversus d h d t for common M but different h0 values coincide into a single curve. Also plots…
The effect of a circular hole on the tensile strength of neat and filled rigid PUR foams
2015
Abstract In order to elucidate the effect of stress concentration on the tensile strength of rigid polyurethane (PUR) foams, specimens with open circular holes and different ratios of hole diameter to specimen width were tested in tension. The reduction in the net-section strength of the specimens with a center hole ranged from 1% to 18% for neat foams and from 18% to 28% for foams produced from a nanoclay-filled PUR. The finite fracture mechanics approach, based on simultaneous application of the strength and fracture mechanics criteria of failure, yielded a reasonably accurate prediction of foam strength in the presence of stress concentration.
Fatigue delamination experiments on GFRP and CFRP specimens under single and mixed fracture modes
2011
This paper deals with the experimental analysis of the delamination phenomena in composite materials under different loading conditions. Quasi-static and fatigue tests are performed on specimens made of glass-fibre (GFRP) and carbon-fibre (CFRP) reinforced plastic. In particular, experiments have been carried out under single fracture modes I and II (using standard DCB and ENF test configurations) and mixed modes I+II (using the MMB test configuration) with several mode mixtures. Results obtained for the two materials have been compared paying attention on the relationship between the parameters that describe the fatigue behaviour and the mode mixture acting during the crack propagation. © …
A theoretical and experimental study to point out the notion of loading mode in damage mechanicsApplication to the identification and validation of a…
2002
A model of fatigue-induced intralaminar cracking in strongly anisotropic laminates is presented. The features of the microscopic phenomenon are explicitly taken into account at the macroscopic level by the use of two variables, which define a new concept in Damage Mechanics that results not only in a coherent model of crack density evolution, but also in a coherent treatment of damage deactivation. Damage evolution indeed is strongly dependent on the local loading mode in each ply where cracking occurs. Experiments on complex lay-ups provided sufficient data for complete calibration of the model. These tests also allowed to validate the theoretical choice of the damage variable. Finally, nu…
A model for predicting the mixed-mode fatigue crack growth in a bonded joint
2013
Bonded joints are highly sensitive to the presence of defects and to the degradation phenomena, and this aspect represents the primary obstacle to their use in different structural engineering applications. Delamination in a bonded joint represents, in fact, one of the primary, most common and insidious causes of damage. In this paper, a numerical–experimental study on the crack propagation along the adhesive layer of a bonded joint specimen is carried out. Experimental study is focused on the evaluation of the damage modalities of a bonded joint when the specimens are subject to fatigue load. Experimental tests are compared with the results of several numerical analysis performed in ANSYS …
Fatigue crack growth of new FML composites for light ship buildings under predominant mode II loading condition
2019
The use of light but strong materials is largely studied in various area of the shipbuilding, this because the need of reducing the weight, and especially the weight of all the structures above the main deck assume primary importance for the stability. Traditionally in fast boats like fast ferries, hydrofoils, patrol boats, the typical materials are Aluminum alloy or composites, both those materials have advantages and disadvantages, but the new development of technologies made possible to combine them, in order to have a new material, combining the advantages of both, in terms of fatigue resistance, firefighting characteristics. In this paper, predominant mode II fatigue delamination tests…
Modeling the Fatigue Damage Evolution in Welded Joints
2017
The present paper presents a two-phase model for the fatigue damage evolution in welded steel joints. The argument for choosing a two-phase model is that crack initiation and subsequent crack propagation involve different damage mechanisms and should be treated separately. The crack initiation phase is defined as the number of cycles to reach a crack depth of 0.1 mm. This phase is modelled based on the Dang Van multiaxial stress approach. Both a multiaxial stress situation introduced by the acting loads and the presence of the multiaxial welding residual stresses are accounted for. The local notch effect at the weld toe becomes very important and the irregular weld toe geometry is character…
Modelling of the fracture toughness anisotropy in fiber reinforced concrete
2015
Steel fiber reinforced concrete is potentially very promising material with unique properties, which currently is widely used in some applications, such as floors and concrete pavements. However, lack of robust and reliable models of fiber reinforced concrete fracture limits its application as structural material. In this work a numerical model is proposed for predicting the crack growth in fiber reinforced concrete. The mixing of the steel fibers with the concrete usually creates nonuniform fibers distribution with more fibers oriented in horizontal direction, than in vertical. Simple numerical models of fiber reinforced concrete require a priori knowledge of the crack growth direction in …
Hybrid equilibrium element with interelement interface for the analysis of delamination and crack propagation problems
2020
This article proposes a formulation for the analysis of delamination and fracture propagation problems at the interelement interface, with perfect adhesion at the pre-failure condition and with linear softening at the post-failure regime. The proposed formulation is based on the hybrid equilibrium element (HEE) model, with stress fields which strongly verify the homogeneous equilibrium equations and interelement equilibrium equations. The HEE can easily model high-order stress fields and can implicitly model the initially rigid behavior of an extrinsic interface at the element sides. The interface model is defined as a function of the same degrees of freedom of the HEE (generalized stresses…
Water-Dependent Blending of Pectin Films: The Mechanics of Conjoined Biopolymers
2020
Biodegradable pectin polymers have been recommended for a variety of biomedical applications, ranging from the delivery of oral drugs to the repair of injured visceral organs. A promising approach to regulate pectin biostability is the blending of pectin films. To investigate the development of conjoined films, we examined the physical properties of high-methoxyl pectin polymer-polymer (homopolymer) interactions at the adhesive interface. Pectin polymers were tested in glass phase (10&ndash