Showing papers by "Paul Robinson published in 2013"

Failure Models and Criteria for Frp Under In-Plane or Three-Dimensional Stress States Including Shear Non-Linearity

Abstract: A set of three-dimensional failure criteria for laminated fiber-reinforced composites, denoted LaRC04, is proposed. The criteria are based on physical models for each failure mode and take into consideration non-linear matrix shear behaviour. The model for matrix compressive failure is based on the Mohr-Coulomb criterion and it predicts the fracture angle. Fiber kinking is triggered by an initial fiber misalignment angle and by the rotation of the fibers during compressive loading. The plane of fiber kinking is predicted by the model. LaRC04 consists of 6 expressions that can be used directly for design purposes. Several applications involving a broad range of load combinations are presented and compared to experimental data and other existing criteria. Predictions using LaRC04 correlate well with the experimental data, arguably better than most existing criteria. The good correlation seems to be attributable to the physical soundness of the underlying failure models.

A detailed finite element investigation of composite bolted joints with countersunk fasteners

Abstract: This paper presents a very detailed FE model of a single lap composite bolted joint, with countersunk fasteners, under static tensile load. The stress states of the CFRP plates and titanium bolts are discussed, the evolution of the contact between the bolts and the holes is analysed, and the numerical results are compared to experimental data. Parametric studies have been performed to study the influence of bolt clamping force, coefficient of friction and bolt–hole clearance on the joint behaviour. It has been found that the model is able to identify correctly the critical locations in the joint (head–shank transition and first thread in bolts and edges of the holes at the faying surface for the plates) and reproduce with accuracy the experimental load–displacement test curves (including an unloading–reloading loop) up to the point where bearing damage occurs. A correlation between the joint stiffness and the contact status between bolts and holes has been found. Five stages have been identified in the joint behaviour: (i) No-Slip, (ii) Slip, (iii) Full Contact, (iv) Damage and (v) Final Failure. The results show that the joint stiffness is higher in the No-Slip stage than in the Full Contact stage, and that this is independent of coefficient of friction and bolt clamping force. The clearance controls the length of the Slip stage and modifies the joint stiffness in the Full Contact stage.

High Performance Composites with Active Stiffness Control

Abstract: High performance carbon fiber reinforced composites with controllable stiffness could revolutionize the use of composite materials in structural applications. Here we describe a structural material, which has a stiffness that can be actively controlled on demand. Such a material could have applications in morphing wings or deployable structures. A carbon fiber reinforced–epoxy composite is described that can undergo an 88% reduction in flexural stiffness at elevated temperatures and fully recover when cooled, with no discernible damage or loss in properties. Once the stiffness has been reduced, the required deformations can be achieved at much lower actuation forces. For this proof-of-concept study a thin polyacrylamide (PAAm) layer was electrocoated onto carbon fibers that were then embedded into an epoxy matrix via resin infusion. Heating the PAAm coating above its glass transition temperature caused it to soften and allowed the fibers to slide within the matrix. To produce the stiffness change the carb...

Response and damage propagation of polymer-matrix fibre-reinforced composites: Predictions for WWFE-III Part A

Abstract: This paper showcases the authors’ predictions for the 13 challenging test cases of the third World Wide Failure Exercise. The cases involve the prediction of lamina biaxial stress–strain curves, ma...