Abstract
Carbon fiber-reinforced polymer (CFRP) laminates, a key composite material, are widely used in aircraft structures and are susceptible to low-velocity impact (LVI) damage from bird strikes, lightning strikes, hail impacts and other situations. Therefore, finding a method that repairs the damaged structure and detects the effect of these repairs under LVI is a very important goal. In this work, the repair effect of LVI damage in CFRP laminates repaired with patches of various sizes is investigated via experimental and numerical nonlinear Lamb wave analyses. An integrated numerical procedure that combines LVI with nonlinear Lamb wave detection is developed to predict the nonlinear Lamb wave behavior in LVI-damaged patch-repaired CFRP laminates. The CFRP laminate damage in the nonlinear Lamb wave simulation is evaluated based on relative acoustic nonlinearity parameters (RANPs). As a result, the integrated numerical procedure is validated with drop-weight impact tests and RAM-5000 SNAP nonlinear ultrasonic detection system. An optimal patch design is established via interpolation to optimize the absorbed energy, delamination surface area, second RANP and third RANP with different patch repair sizes. These parameters exhibit consistent curve fitting trends, indicating that they can be used as important indicators of impact damage. The optimal circular patch design with a radius of 2.5 r has better impact resistance behavior and repair performance.
Highlights
Carbon fiber-reinforced polymer (CFRP) laminates are key materials for the development of science and technology in aerospace, national defense, biomedical and other high-tech fields due to their excellent performance [1,2]
The three-dimensional (3D) Hashin damage criteria [34,35] and damage evolution are effectively applied in many numerical simulations to predict the intralaminar damage initiation and progressive failure process of CFRP laminates that were repaired with patches of various sizes
According to the experimental and numerical results, the nonlinear Lamb wave propagation behaviors of the low-velocity impact (LVI)-damaged CFRP laminates that were repaired with patches of various sizes are discussed, and the correctness of the finite element (FE) model strategy is verified by comparing these results
Summary
Carbon fiber-reinforced polymer (CFRP) laminates are key materials for the development of science and technology in aerospace, national defense, biomedical and other high-tech fields due to their excellent performance [1,2]. With the extensive use of composite materials in aircraft structures, many impact-related accidents will inevitably occur, such as bird strikes, lightning strikes, hail impacts and other situations. These impact energies are small but result in barely visible impact damage (BVID), posing a substantial potential threat to the safety of aircraft composite structures [4]. To satisfy the production requirements and reduce the maintenance costs, especially for large and expensive equipment, composite structures that have sustained small impact damage are usually repaired rather than replaced [5,6,7]. In daily routine maintenance and within their service lives, CFRP laminates repaired with external patches are still vulnerable to LVI damage from other foreign objects. The SHM method based on nonlinear Lamb waves is currently considered to be a promising method for use in the aviation field [9]
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