Blog posts

Rajat Arora       Amit Acharya

We present a framework which unifies classical phenomenological J2 and crystal plasticity theories with quantitative dislocation mechanics. The theory allows the computation of stress fields of arbitrary dislocation distributions and, coupled with minimally modified classical (J2 and crystal plasticity) models for the plastic strain rate of statistical dislocations, results in a versatile model of finite deformation mesoscale plasticity. We demonstrate some capabilities of the framework by solving two outstanding challenge problems in mesoscale plasticity: 1) recover the experimentally observed power-law scaling of stress-strain behavior in constrained simple shear of thin metallic films inferred from micropillar experiments which all strain gradient plasticity models overestimate and fail to predict; 2) predict the finite deformation stress and energy density fields of a sequence of dislocation distributions representing a progressively dense dislocation wall in a finite body, as might arise in the process of polygonization when viewed macroscopically, with one consequence being the demonstration of the inapplicability of current mathematical results based on $\Gamma$-convergence for this physically relevant situation. Our calculations in this case expose a possible 'phase transition'-like behavior for further theoretical study. We also provide a quantitative solution to the fundamental question of the volume change induced by dislocations in a finite deformation theory, as well as show the massive non-uniqueness in the solution for the (inverse) deformation map of a body inherent in a model of finite strain dislocation mechanics, when approached as a problem in classical finite elasticity.

Paper can be found at link Finite_Deformation_Dislocation_Mechanics.

Dear Colleagues,

We invite you to submit your relevant work to a mini-symposium on “Damage And Thermo-Chemo-Mechanical Coupling In Polymers” (full description below) at the 2020 Society of Engineering Science. SES 2020 will be held at the University of Minnesota in Minneapolis, September 28-30th.

We also like to announce that Prof. Ellen Arruda will give the keynote of this symposium. 

Adhesive contact of a rigid flat surface with an elastic substrate having Weierstrass surface profile is numerically analyzed using the finite element method. In this work, we investigate the relationship between load and contact area spanning the limits of non-adhesive normal contact to adhesive contact for various substrate material properties, surface energy and roughness parameters. In the limit of non-adhesive normal contact, our results are consistent with published work.

Arc welding based additive manufacturing or WAAM techniques are attracting interest from the manufacturing industry because of their potential to fabricate large metal components with low cost and short production lead time. This process exists alongside other high deposition rate metal AM technologies such as powder and wire based DED. While these use either laser or an electron beam as energy source to melt a metal powder or wire, WAAM technologies melt metal wire using an electric arc.

Over the last years, UGent-MMS has developed the stand-alone BladeMesher software for generating finite element models of large wind turbine blades. The software reads in the material data and airfoil data of the wind turbine blade, and automatically constructs the geometry and finite element mesh for the blade. In a next step, the nodal and element information of the finite element mesh is written out to an input file for a commercial finite element solver (Abaqus in this case).

Thermoplastic composites are gaining more and more interest in automotive, aerospace and sports applications, because of the short cycle times and recycling possibilities. Besides short fibre-reinforced thermoplastics, also continuous fibre-reinforced thermoplastic composites are being considered for load-carrying structures. However, their behaviour during manufacturing and during in-service use is very different from the traditional thermoset composites (typically epoxy-based). The mechanical properties of thermoplastic composites are much more sensitive to temperature and loading rate.