Amirkabir University of Technology

About: Amirkabir University of Technology is a education organization based out in Tehran, Iran. It is known for research contribution in the topics: Nonlinear system & Fuzzy logic. The organization has 15254 authors who have published 31165 publications receiving 487551 citations. The organization is also known as: Tehran Polytechnic & Tehran Polytechnic University.

Failure mode transition in AHSS resistance spot welds. Part I. Controlling factors

Abstract: Failure mode of resistance spot welds is a qualitative indicator of weld performance. Two major types of spot weld failure are pull-out and interfacial fracture. Interfacial failure, which typically results in reduced energy absorption capability, is considered unsatisfactory and industry standards are often designed to avoid this occurrence. Advanced High Strength Steel (AHSS) spot welds exhibit high tendency to fail in interfacial failure mode. Sizing of spot welds based on the conventional recommendation of 4t0.5 (t is sheet thickness) does not guarantee the pullout failure mode in many cases of AHSS spot welds. Therefore, a new weld quality criterion should be found for AHSS resistance spot welds to guarantee pull-out failure. The aim of this paper is to investigate and analyze the transition between interfacial and pull-out failure modes in AHSS resistance spot welds during the tensile–shear test by the use of analytical approach. In this work, in the light of failure mechanism, a simple analytical model is presented for estimating the critical fusion zone size to prevent interfacial fracture. According to this model, the hardness ratio of fusion zone to pull-out failure location and the volume fraction of voids in fusion zone are the key metallurgical factors governing type of failure mode of AHSS spot welds during the tensile–shear test. Low hardness ratio and high susceptibility to form shrinkage voids in the case of AHSS spot welds appear to be the two primary causes for their high tendency to fail in interfacial mode.

Fabrication and characterization of polyurethane electrospun nanofiber membranes for protective clothing applications

Abstract: Received 18 July 2011; accepted 25 November 2011DOI 10.1002/app.36611Published online 20 March 2012 in Wiley Online Library (wileyonlinelibrary.com).ABSTRACT: Electrospun nanofibrous webs are impor-tant in nanotechnology applications due to their high sur-face area and interconnected porosity. In this study, theeffect of electrospinning duration on some physical andmechanical properties of polyurethane (PU) electrospunwebs is investigated for potential applications such as pro-tective clothing and membranes. The results show that thethickness and weight of webs and subsequently their ten-sile strength increase linearly with the electrospinning du-ration. Air permeability of nanofibrous webs decrease andhydrostatic pressure increases nonlinearly while watervapor permeability remains constant. This work showsthat air permeability of PU webs follows Fick’s law of dif-fusion. Some regression models have been proposed todescribe electrospun membranes behavior. The results ofthis investigation indicate that this new generation ofnanofibrous materials has a good potential for applicationas membrane in protective clothing.