Search results for "Ultima"
showing 10 items of 396 documents
23.1: Invited Paper: Models and Experiments of Mechanical Integrity for Flexible Displays
2008
Flexible displays present a challenging problem in terms of mechanical integrity, a result of the considerable hygro-thermo-mechanical contrast between the inorganic, brittle device layers and the compliant polymer substrates. This paper reviews the main approaches to study and identify the key factors, which control the mechanical stability of this class of displays. Focus is put on the analyses of residual stress and damage under tensile loading. Novel electro-mechanical methods are used for accurate insight into critical phenomena. An important result is that the thickness and stiffness of the substrate control the critical strain for failure of the device layers.
Behaviour of concrete deep beams with openings and low shear span-to-depth ratio
2012
Abstract The goal of this study is to experimentally and analytically evaluate the influence of circular openings in reinforced concrete deep beams with low shear span-to-depth ratio. Twenty reinforced concrete small-scale deep beams with or without openings were tested in flexure under four-point loading. The beams had a small shear span-to-depth ratio in order to stress the shear behavior. The specimens had different reinforcement arrangements and opening positions. The load was transmitted to the specimen with bearing plates having the same side length as the beam. Two LVDT’s were arranged to record the transverse and axial strain of the theoretical struts forming in the beam. Additional…
Simple Plastic Model for Shear Critical SFRC Beams
2010
A simple physical model, for prediction of ultimate shear strength of steel fiber reinforced concrete (SFRC) beams is developed on the basis of a plastic approach originally proposed for reinforced concrete (RC) beams without stirrups. It is founded on the hypothesis that cracks can be transformed into yield lines, and thus is know as Crack Sliding Model (CSM). First, the CSM is improved in order to take into account the shear strength increase for deep beams, due to the arch effect. Then, the effectiveness factors for fibrous concrete under biaxial stresses are evaluated, taking into account the post-cracking tensile strength of SFRC and its ability to control slippage along shear cracks. …
Damage accumulation under variable amplitude loading of welded medium- and high-strength steels
2004
Abstract The paper presents the calculation of cumulative damage for two types of welded joints (butt weld and transverse stiffeners) of four steels (medium to high strength): S355N, S355M, S690Q and S960Q. This calculation is based on experimental data obtained under axial loading and bending with constant and variable amplitudes (Gaussian distribution and Gauss with overload spectrum). The experiments were performed under fully reversed ( R =−1) and pulsating ( R =0) loading. The fatigue life is calculated using the modifications of the Palmgren–Miner–Original rule, according to the Palmgren–Miner–Elementary method, as well as to Haibach’s suggestion. The fatigue life does not depend on t…
Residual stresses in friction stir welded parts of complex geometry
2011
Residual stresses play a key role on the mechanics underlying the fatigue crack growth propagation of welded joints. Indeed, compressive residual stresses may induce a beneficial enhancement of the fatigue life under loading condition whereas tensile residual stresses may act to increase the stress distribution at crack tip, resulting in a life-threatening condition of the welded structure. In-process distortion and final geometry of welded joints are also affected by residual stresses. In this paper, the longitudinal residual stress distributions in friction stir welding (FSW) joints were investigated for butt and skin–stringer geometries, including lap and T configurations. To measure res…
Critical Planes in Multiaxial Fatigue
2005
The paper includes a review of literature on the multiaxial fatigue failure criteria based on the critical plane concept. The criteria were divided into three groups according to the distinguished fatigue damage parameter used in the criterion, i.e. (i) stress, (ii) strain and (iii) strain energy density criteria. Each criterion was described mainly by the applied the critical plane position. The multiaxial fatigue criteria based on two critical planes seem to be the most promising. These two critical planes are determined by different fatigue damage mechanisms (shear and tensile mechanisms).
A Cap-Model for Masonry-Like Material Constitutive Laws
1995
An accurate description of the constitutive behaviour of masonry-like materials is an essential target for obtaining an effective analysis-tool of masonry structures. In this paper an idealized constitutive model of such materials is proposed taking into account some peculiar features of masonry: -i) a limited strength in compression; -ii) a very limited ability to withstand tensile stresses; -iii) a softening behaviour due to a progressive reduction of the tensile strength during a monotonically increasing loading.
Study of the Formability of Light Metallic Materials
2015
There is a continuing interest in using laminated materials for the production of lightweight parts, the resulting parts having the same functionality and even an increased stiffness and length of operation compared to conventional materials. The present paper aims to study the forming behavior of the laminated materials that requires the unfolding of tests to determine the tensile mechanical properties and the intrinsic properties, determining the forming limit curves by means of the Nakajima test and the analysis of the behavior at unconventional incremental forming.
Tensile behaviour of patch-repaired CFRP laminates
2011
The present study examines the tensile behaviour of composite structures repaired by bonding external patches. Various patches of different stacking sequences placed on both sides of the parent plate were considered. Damage development and the failure process of the repaired plates were analyzed and a parent plate fracture model has been proposed. Optimised patch repairs were calculated by finite element modelling. It was found that high stress concentration along the longitudinal edges of circular patches and/or at the transverse edges of the hole leads to early damage initiation in the parent plate. However, the position of damage initiation and the process of damage progression depend pa…
Parametric study of laser welding of copper to austenitic stainless steel
2018
Abstract Welding of copper to stainless steel is challenging because of sharp difference in thermophysical properties of materials and the presence of miscibility gap in Fe-Cu system. The parametric study of continuous Yb:YAG laser welding between copper and austenitic stainless steel 316L has been performed. The influence of laser power, welding speed and beam offset from joint line on weld composition, microstructure and tensile properties was studied. The corrosion behaviour of the welds was evaluated in 0.1M NaCl with the potentiostatic pulse testing method, salt fog and immersion tests. In function of copper dilution in the melted zone, different types of microstructure were observed: …