OPTIMAL DESIGN OF A COMPOSITE SCARF REPAIR PATCH UNDER TENSILE LOADING

ABSTRACT Mechanics of the composite scarf repair under tensile loading with and without overlay plies was examined for nontraditional patch ply orientations. Three-dimensional nonlinear analysis was performed for repair failure prediction and good baseline comparison for open-hole scarfed panels and panels repaired by using standard ply-by-ply replacement patch composition was achieved. Multidimensional optimization was performed to calculate the repair patch ply orientations which minimize the von Mises stresses in the adhesive. These optimal stacking sequences achieved significant reduction of the stress levels and resulted in predicted up to 75% and 85% strength restoration for flush and single ply thickness over-ply repair. These results are intended to illustrate additional design variables available for efficient composite repair design, namely the composition of the repair patch

Optimal Design of a Composite Scarf Repair Patch Under Tensile Loading

Mechanics of the composite scarf repair under tensile loading with and without overlay plies was examined for nontraditional patch ply orientations. Three-dimensional nonlinear analysis was performed for repair failure prediction and good baseline comparison for open-hole scarfed panels and panels repaired by using standard ply-by-ply replacement patch composition was achieved. Multidimensional optimization was performed to calculate the repair patch ply orientations which minimize the von Mises stresses in the adhesive. These optimal stacking sequences achieved significant reduction of the stress levels and resulted in predicted up to 75% and 85% strength restoration for flush and single ply thickness over-ply repair. These results are intended to illustrate additional design variables available for efficient composite repair design, namely the composition of the repair patch.</jats:p

Simulation of Discreet Damage Evolution in Laminated Composite Compact Tension Specimens

Damage progression in laminated Overheight Compact Tension specimens was modeled using discrete representations of individual cracks and delaminations. Matrix cracking and delamination initiation, propagation, and interaction, without any prior knowledge and/or meshing of matrix cracking surfaces, is accomplished by combining stress and fracture mechanics-based constitutive modeling within a mesh independent crack-modeling framework. Simulation results including only matrix damage for specimens with [452/902/−452/02]s and [04/904]2s stacking sequences were compared with load-displacement curves and 3D X-ray micro computed tomography results from tested specimens. Excellent correlation was shown between the simulated and experimental load-displacement curves including statistical variations and proper representation of both the curve non-linearity and peak load. Similarly, remarkable correlation between simulated and experimental damage extent was shown. Additionally, a [45/90/−45/0]2s specimen exhibiting significant fiber fracture was modeled and results compared with experiment. Fiber fracture was simulated using a continuum damage mechanics approach in addition to the discrete cracking and delamination damage representations of matrix damage. The simulated load displacement curve and damage extent compared favorably with experimental results.</jats:p

Optimal design of a composite scarf repair patch under uniaxial tension load

An optimal design algorithm was used to determine the repair fiber angles that minimize the stress in the adhesive of the repair joint. The strength was predicted by analysis using the Critical Failure Volume (CFV) approach for fiber failure. Excellent agreement was seen between predicted and tested strengths

Optimization of a composite scarf repair patch under tensile loading

Mechanics of the composite repair under tensile loading with and without overlay plies was examined for nontraditional patch ply orientations. Three-dimensional nonlinear analysis was performed for repair failure prediction and good baseline comparison for open hole scarfed panels and panels repaired by using standard ply-by-ply replacement patch composition was achieved. Multidimensional optimization was performed to calculate the repair patch ply orientations which minimize the von Mises stresses in the adhesive. These optimal stacking sequences achieved significant reduction of the stress levels and resulted in predicted up to 85% and 90% strength restoration for flush and single ply thickness over-ply repair. These results are intended to illustrate additional design variables available for efficient composite repair design, namely the composition of the repair patch

Selected topics in modeling and simulation of inelastic behaviors of polymer matrix composite materials at AFRL

The Composites and Hybrid Materials Branch, Materials and Manufacturing Directorate of the Air Force Research Laboratory (AFRL/RXBC), is concerned with development, characterization and application of organic and hybrid materials for challenging aerospace service environments. This talk will describe highlights of efforts concerning the modeling and experimental characterization of composite materials associated with both present and future applications involving reactive degradation and damage. Polymer composites applied to extreme temperature environments such as experienced by engine components and extreme lifetimes as would be anticipated from the extended use of current platforms, provide examples of situations requiring modeling of the described types for purposes of performance and life prediction. In general, the described behaviors involve coupled influences and responses, and thermodynamic bases for the models, when available, permit the solution space to be restricted to physically meaningful results to problems specified in these complex conditions. Features of: thermodynamic mixture theory for anisotropically reacting materials; micromechanical approaches; experimental characterization of thermo-oxidative behaviors of polymer composites at high temperatures; and developments in discrete crack-based modeling of the damage and failure processes of materials with complex failure modes and statistical inhomogeneities, and possibly complex architectures, will be highlighted. © AES-Advanced Engineering Solutions