School of Mechanical Engineering Seminar
Wednesday, November 7, 2018 at 14:00
Nearly Mode I Fracture Toughness and Fatigue Delamination Propagation in a Multi-Directional Laminate Fabricated by a Wet-Layup
Tomer Chocron
Student of Professor Banks-Sills
School of Mechanical Engineering, Faculty of Engineering,
Tel Aviv University, Ramat Aviv, 69978, Israel
tomerchocron@mail.tau.ac.il
Double cantilever beam (DCB) specimens were first tested quasi-statically to obtain a 
resistance curve. In addition, fatigue delamination propagation tests were also carried out to obtain a Paris-type relation, which describes the delamination propagation rate 
, where 
is the delamination length and 
is the cycle number. The tests were performed for two cyclic displacement ratios 
of 0.1 and 0.48. Finite element analyses were carried out to obtain results of the energy release rate. The specimens were fabricated by means of a wet-layup from carbon fiber reinforced polymer plies. The interface containing the delamination was between a unidirectional fabric and a woven ply.
Results will be presented with an expression for determined. Moreover, the fatigue data will be described including techniques for calculating and in each cycle of the tests. Furthermore, a method for obtaining threshold values will be presented. Finally, master-curves which eliminate the dependence on the -ratio will be described and a back-calculation of values in a range greater than that in the tests will be shown, as well. These results shed light on the behavior of delamination propagation in multi-directional laminate composites for nearly mode I deformation.
Ballistic penetration analysis in soft laminated composites
Raz Chricker
MSc Student of Prof. Rami Haj-Ali
High strength and high stiffness materials such as Dyneema® and Kevlar® fiber based composites are often used in protective armor applications. The latter require energy absorption and penetration resistance against threats, such as metallic projectiles. The high strength to weight ratio is one of the main reasons for using these soft composites in ballistic impact applications.
Experimental testing along with finite element (FE) modeling are the two major approaches for investigating ballistic behaviors of composite targets. The present study combines these two approaches, in part by introducing new multi-scale FE parametric analyses aimed at predicting experimental ballistic tests previously conducted at Plasan Inc. Two distinct material models are presented. The first is a meso-scale sublaminate model of the Dyneema [0/90] cross-ply laminate. The second is a discrete model used to describe the woven Kevlar system at the yarn level. The sublaminate model is implemented within an explicit-dynamic FE code and represents the material points within each element assuming a periodic stacking of repeated cross-ply configuration through the thickness. The orthotropic layers in the sublaminate are held by a cohesive layer. Once critical values of stresses are reached, the model allows failure of an element in three major mechanisms: fiber tensile fracture, delamination, and out of plane shearing of the layer.
Quantitative results of ballistic impact simulations show good correlation compared to the experiments. Moreover, the simulations include evidence of capturing the main energy absorption mechanisms under high velocity impact. The proposed modeling approach can be used as an effective armor design tool.
