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In automotive industry, the FE fatigue analysis of mechanical structures made of steel thin walled parts and seam welded assemblies uses a dedicated technique based on shell element modelling for components and on 1D rigid elements for welds. This method has been validated with several intensive fatigue test campaigns using gas metal arc welded samples with different assemblies, for both bending and torsional loads. The fatigue results are relative to crack initiation at the weld toe with bending normal stress or with longitudinal shear stress for several load ratios. The purpose of the current work is the transposition of the initial method to another FE welded model. In a recent IIW guideline for the assessment of weld root fatigue, a shell element weld model has been proposed for seam weld fatigue assessment in case of weld root crack initiation. The idea is to analyse the possible extension of this FEA weld element model for weld toe fatigue analysis and several comparisons of stress results are detailed and discussed. Different fatigue criteria are used to verify the correlation with the fatigue test results. First, the approach is based on maximum shear stress, then structural stress is calculated and results are compared to IIW S/N curves.

Abstract: In this article, we illustrate the main advanced magnetic resonance imaging (MRI) techniques used for imaging of the spine and spinal cord in children and adults. This work focuses on daily clinical practice and aims to address the most common questions and needs of radiologists. We will also provide tips to solve common problems with which we were confronted. The main clinical indications for each MR technique, possible pitfalls and the challenges faced in spine imaging because of anatomical and physical constraints will be discussed. The major advanced MRI techniques dealt with in this article are CSF, (cerebrosopinal fluid) flow, diffusion, diffusion tensor imaging (DTI), MRA, dynamic contrast-enhanced T1-weighted perfusion, MR angiography, susceptibility-weighted imaging (SWI), functional imaging (fMRI) and spectroscopy.Teaching Points: • DWI is essential to diagnose cord ischaemia in the acute stage.• MRA is useful to guide surgical planning or endovascular embolisation of AVMs.• Three Tesla is superior to 1.5 T for spine MR angiography and spectroscopy.• Advanced sequences should only be used together with conventional morphological sequences. [ABSTRACT FROM AUTHOR]

Industrial structures undergo complex loading often unsuitable for the design and validation phases of their development. Engineers seek simplified signals to replace them, yet equivalent in terms of fatigue. A general framework for the construction of fatigue equivalent loads is presented, intended to take into account some uncertainty on the structure to which it will apply. The guiding idea is to describe this uncertainty thanks to parameters of a model of the structure, and then to assure the equivalence of damage or failure behavior over the whole range of expected parameters. The approach is applied in the case of structures undergoing multiple inputs of concentrated force.

Relations between existing spot-weld finite element models and the mechanical behaviour of spot-weld are investigated for fatigue design application. Specifically, the different zones that constitute the numerical model are interrogated with respect to physical observation. In order to identify the Mechanical Influence Area of the Spot-Weld here designated as “MIASW” we propose a methodology to determine numerically its size. Hence, we develop a finite element coupon representing a spot-weld under a basis of four unit load cases. The coupon provides mechanical quantities of interest that allows us to characterize the spot-weld response that shell element are unable to represent. This response is crucial to be captured for further fatigue analysis.