Papers by Keyword: Compression after Impact (CAI)

Abstract: Composite stiffened panels are widely used in the modern aircraft structure with the advantages of light weight, structural efficiency and good crack performance. But the stiffened panels have poor performance at thickness direction, especially for low-velocity impact. First of all, compressive tests were investigated and analyzed for two types of composite stiffened panels, which are integrated specimens and post-impact specimens. And the effect of low-velocity impact to the supporting capacity of composite stiffened panels was researched. Secondly，the finite element model was established to simulate the CAI (Compression After Impact)strength with the equivalent hole method. It is found that the analyze results match the experimental results well. According to the experimental results, structural damage and the maximum load caused by impact energy are scattering. Then the imperfect factors were introduced to reflect the initial imperfection, namely the initial deflection at thickness direction. The effect of different imperfect factors to the maximum load was discussed.

Abstract: Fiber-reinforced plastic is attractive as a material that can replace metal. It has been widely used in various engineering fields involving aircraft, ships, and automobiles. Currently, personal safety is an important automobile issue. Improvements in pedestrian safety technology, particularly, are required in order to improve vehicles' impact-absorbing performance. In this study, materials with good impact properties that are lightweight and easy to design with will be considered. In other words, a composite is required that has high toughness and high fracture energy while not being brittle. A method for evaluating the compressive strength after impact using a compression after impact (CAI) test has been adopted. New hybrid FRPs that are lightweight and have good impact properties can now be developed.

Abstract: This paper presented the effect of constituent materials on impact damage and strength reduction of sandwich structure, composed of laminated woven E-glass facesheets and polypropylene thermoplastic honeycomb core. Effect of low-velocity impact was the main interest in a variety of layered configurations. Compression after impact (CAI) has been carried out to determine the residual strength of impacted sandwich structures. Three different thicknesses of core of 20, 40 and 60mm subjected to three different levels of impact energy of 15, 30 and 45J were investigated. Impact response of the panel was recorded and analyzed in terms of peak load, indentation, energy absorbed and time. A profile analysis using optical 3D surfaces profiler was carried out to attain the indentation depth and damage area of the samples. The tested samples were then sectioned into halves to capture the failure mode or damaged sequence of the polypropylene thermoplastic honeycomb core. The dominant failure modes of the core indicated that polypropylene thermoplastic honeycomb core is a high strength material which can absorb higher impact energy and retain a higher degree of structural integrity.

Abstract: The influence of nanoclay on the impact damage resistance of carbon fiber-epoxy (CFRP) composites has been investigated using the low-velocity impact and compression after impact tests. The load-energy vs time relations were analyzed to gain insight into the damage behaviors of the materials. Compression-after-impact (CAI) test was performed to measure the residual compressive strength. The CFRPs containing organoclay brought about a significant improvement in impact damage resistance and damage tolerance. The composites containing organoclay exhibited an enhanced energy absorption capability with less damage areas and higher CAI strengths compared to those made from neat epoxy. A 3wt% phr was shown to be an optimal content with the highest damage resistance.

Abstract: A finite element model is proposed to determine the residual strength and the evolution of damage area of indented sandwiches structures with Nomex honeycomb core and metallic skins indented by a spherical indenter under longitudinal compression load (CAI). The honeycomb is represented by a grid of non-linear springs which its behavior law is obtained by performing simple transverse uniform compression test on a block of honeycomb alone.The comparisons between computation and test result show that the model can simulate accurately the form of damage geometry during indentation, its residual print when the load is relieved (relaxation) and the residual strength and the evolution of damage geometry during CAI.

Abstract: The objectives of this study are to evaluate the internal damage and compressive residual strength of composite laminate by impact loading. To investigate the environmental effects, as-received and accelerated-aged glass/phenolic laminates are used. UT C-Scan is used to determine the impact damage characteristics and CAI tests are carried out to evaluate quantitatively the reduction of compressive strength by impact loading. The damage modes of the woven glass/phenolic laminates are evaluated. In the case of the accelerated-aged laminates, as aging time increases, initial failure energy and residual compressive strength decrease.