Carbon Fiber Reinforced Polymer Facesheets Research Articles

On the impact damage resistance and tolerance improvement of hybrid CFRP/Kevlar sandwich composites

This work presents an experimental demonstration of the significant improvement in the damage resistance of carbon fiber reinforced polymer (CFRP) Kevlar sandwich composite laminates under impact and compression after impact loads. A core of Kevlar plies was sandwiched between two face sheets of CFRP, representing two-third the global laminate thickness. Hand lay-up and vacuum bagging were used to manufacture the sandwich composite structure. Tests of low velocity impact and compression after impact (CAI) were performed to characterize the damage resistance. The different damage modes and their sequence during low velocity impact were visualized using microcomputed tomography. The results showed different damage levels in CFRP/Kevlar core laminates at low and high impact energies. At low impact energy, 10 J, few matrix cracks and delaminations were the main damage modes inside CFRP/Kevlar core laminate, however, extensive delamination, matrix cracks and fiber cut at the lower part of the laminate were appeared inside the fully CFRP laminate. At high impact energy, 70 J, fiber cut was observed inside the whole CFPR laminate, however, for CFRP/Kevlar core laminate, the lower CFRP face sheets did not suffer from any kind of damage. This allowed CFRP/Kevlar core laminate to sustain large load after the load drop occurred when the maximum load capacity of the laminate is reached. Moreover, it allowed CFRP/Kevlar core laminate to sustain larger compressive load during CAI tests resulting in improved residual CAI strength. Owing to the low density of Kevlar fibers and lower damage level during impact (better damage resistance), CFRP/Kevlar core laminate showed up to 51% larger specific CAI strength than CFRP laminate (better damage tolerance).

The flexural behavior of the epoxy and polyester based composite sandwich structures at subzero temperatures

The present work aims at characterizing the 3D woven spacer composites with carbon fiber reinforced polymer face-sheets under the 3-point flexural test at subzero temperature conditions. For this purpose, sandwich composite panels are manufactured using vacuum assisted resin infusion method for epoxy and polyester matrix materials with 2, 3, and 4 layered face-sheets. The 3-point flexural test was performed for warp and weft direction on liquid nitrogen temperature (−40 °C). Macroscopic fracture morphology was examined to understand the deformation and failure mechanism. The results show that the flexural properties were significantly affected by the number of face-sheets and then from matrix material and finally from the composite direction at subzero temperatures.

X-ray micro-computed tomography analysis of impact damage morphology in composite sandwich structures due to cold temperature arctic condition

In this study, X-ray micro-computed tomography is employed to characterize the impact damage mechanisms in foam core sandwiched composites, paying particular attention to the influence of extreme low temperature effects. Investigation on impact response reveals that more energy absorption with lower impact damage force occurs at lower temperature. Results evidently show that test temperature has a significant influence on the impact damage behavior. Post-mortem inspection portrays clear relationships between damages in both foam core and carbon fiber reinforced polymer facesheets, as well as exposed test temperature. Specimens impacted at extreme low temperature (−70℃) exhibit less strength, and higher susceptibility to damage, verified by severer penetration of the impactor. Micro-computed tomography is exploited to examine cross-sectional views of the impacted specimens, showing detailed damage mechanisms of the carbon fiber-reinforced polymer facesheets and the foam core, thereby evidently revealing multiple complex impact damage modes such as fiber breakage, delamination, core shearing and crushing, facesheet-core debonding, which are all strongly influenced by arctic low temperature. The findings of this work will lead to improved design for advanced composite structures with enhanced impact resistance and damage tolerance in extreme cold environment particularly in the arctic region.

Low-Velocity Impact Properties of Sandwich Structures with Aluminum Foam Cores and CFRP Face Sheets

Within this contribution, the low-velocity impact behavior of sandwich structures was investigated. The sandwich structures consisted of carbon fiber reinforced polymer (CFRP) face sheets in various setups, and different core structures, including an open-cell and a closed-cell aluminum foam. The matrix of the face sheets was foamed polyurethane, which also acts as the adhesive connecting the face sheets to the core. Low-velocity indentation tests were carried out with multiple sandwich configurations. The indentation behavior was further examined by additional quasi-static indentation tests, and in situ indentation tests sequentially recorded by X-ray computed tomography. Both the low velocity indentation tests and the quasi-static tests were supported by digital image correlation measurements of the lower specimen surfaces. The overall indentation behavior was described consistently to sandwich structures with different material combinations in literature. The influence of each sandwich configuration parameter on the indentation behavior was determined and described in detail.

Cohesive zone modeling for mode I facesheet to core delamination of sandwich panels accounting for fiber bridging

A new cohesive zone traction-separation law, which includes the effects of fiber bridging, has been developed, implemented with a finite element (FE) model, and applied to simulate the delamination between the facesheet and core of a composite honeycomb sandwich panel. The proposed traction-separation law includes a standard initial cohesive component, which accounts for the initial interfacial stiffness and energy release rate, along with a new component to account for the fiber bridging contribution to the delamination process. Single Cantilever Beam tests on aluminum honeycomb sandwich panels with carbon fiber reinforced polymer facesheets were used to characterize and evaluate the new formulation and its finite element implementation. These tests, designed to evaluate the mode I toughness of the facesheet to core interface, exhibited significant fiber bridging and large crack process zones, giving rise to a concave downward/concave upward pre-peak shape in the load–displacement curve. Unlike standard cohesive formulations, the proposed formulation captures this observed shape, and its results have been shown to be in excellent quantitative agreement with experimental load–displacement results, representative of a payload fairing structure, as well as local strain fields measured with digital image correlation.

Experimental study on the flexural properties of 3D integrated woven spacer composites at room and subzero temperatures

The flexural behavior of the 3D integrated woven spacer composites with carbon fiber-reinforced polymer face sheets are performed with epoxy and polyester matrix in the warp direction. The static loading of foam core carbon/epoxy and carbon/polyester composite sandwich panels in three-point flexural test was characterized at room temperature (23℃) and at liquid nitrogen temperature (−40℃). Macro-fracture morphology and progress have been examined to understand the deformation and failure mechanism. Significant increases in the flexural strength with brittle type core shear failure were observed at low temperatures as compared with the corresponding room temperature behavior. The performance of the epoxy-based composite is compared to the polyester one. Significant changes in the flexural properties of the composites have been found, first related to the temperature and then to the resin type. The flexural properties of the epoxy-based composites were affected greatly by temperature and exhibited higher flexural performance than polyester-based composites at low temperatures.

Response of sandwich structures with pyramidal truss cores under the compression and impact loading

In this paper, the pyramidal truss core sandwich structures consisting of carbon fiber reinforced polymer (CFRP) facesheets and aluminum alloy cores were manufactured based on the slot-fitting method. This hybrid concept is to maximize the specific bending stiffness/strength as well as obtain excellent energy absorption ability. Quasi-static compression tests were conducted to get the stress–strain curves and to evaluate the energy absorption mechanism. Low velocity impact tests were carried out to investigate the damage resistance of such structures. The compressive measurements show that the low density aluminum alloy pyramidal truss cores have superior energy absorption ability compared with other lightweight lattice cores. In the impact tests, the failure of matrix cracking, fiber breakage, delamination of CFRP facesheets and buckling of truss members occurred and the extent of damage was significantly affected by the impact site. In addition to experimental testing, finite element models for compression and impact simulations have been developed using ABAQUS software. The numerical results were validated compared with the experimental tests.