Impact modeling of foam cored sandwich plates with ductile or brittle faceplates

This paper reports numerical results of low velocity impact on open-face sandwich plates with an impactor of 2.65 kg mass hitting with 6.7 m/s velocity. The numerical simulation is done using 3D finite element models in LS-DYNA. The sandwich plates used for the present work have a core made of commercial aluminum alloy foam (Alporas) with faceplates made of either ductile aluminum (Al) or brittle carbon fiber reinforced plastic (CFRP). Selection of suitable constitutive models and erosion criterion for the failure analysis is investigated. A simplified analytical model for the peak load prediction under punch-through failure mode is presented. Numerically predicted contact force versus time, energy absorbed versus time along with the failure modes are compared with the experimental measurements and observations. Within experimental scatter, there is a good agreement between the numerical predictions and experimental measurements. Further more, the analytically predicted peak load values are in excellent agreement with the experimental measurements

Comparative study of composite scarf and strap joints for equivalent repair signature under uniaxial tension

Scarf joints are preferred in aerospace composite repairs that offer better strength, flushed surface and nearly uniform shear and peel stress distribution along the bond length. However, a shallow scarf angle repair of 2° to 3° as practiced requires significant parent material removal thus increasing the repair signature and cost. Scarfing the single side accessible, multi-layered composite structures is difficult. Herein, different repair designs based on 8.6° scarf, thin CFRP strap (0.5 mm and 1.1 mm), 0.5 mm thin Ti-6Al-4V straps (with and without pins) are used in bonding CFRP composites, their repair strength is measured through tensile testing. Results show that the failure load of the scarf and Ti-6Al-4V strap joints are similar implicating that the higher scarf angle designs can be replaced with Ti-6Al-4V straps for better repair efficacy. Failure analysis depicts that delamination due to the inner edge peel stresses is a critical failure mode of the strap repaired joints.This work was conducted within the Rolls-Royce@NTU Corporate Lab under the project “ARMS 1.3 Repair of Composite Aero-engine Structures” with support from the Industry Alignment Fund (IAF) Singapore under the Corp Lab@University Scheme

Influence of stiffener configuration on post-buckled response of composite panels with impact damages

In this paper, the effect of T, I and J stiffer configurations on post-buckling response of composite stiffened panels with impact damage is investigated through experiments and numerical simulations. Two identical panels in all three configurations were designed and manufactured. Each panel has four stringers of the same type. All panels were designed to have a skin buckling load of 92 kN ± 5 kN and weight of 1.45 kg ± 0.05 kg to separate the effect of impact damage irrespective of stiffener type. One panel from each configuration is impacted with 50 J energy above stiffener flange from skin side to create a Barely Visible Impact Damage (BVID) and followed by a compression test till collapse. A comparative study between pristine and impacted panels is presented. The effect of impact damage on buckling load, post-buckling response, collapse load and end-shortening were investigated. Moreover, finite element numerical models were developed for all panels which include intra-laminar and inter-laminar damage initiation and growth models. Impact damage area measured from ultrasonic C-scan was modelled in commercial finite element software Abaqus®. Failure modes in pristine and impacted panels such as disbond, tearing of stiffener web and locations from experiments are discussed and validated by numerical simulations