Low velocity impact analysis on CFRP
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Low Velocity Impact Analysis on CFRP
Introduction to Low Velocity Impact on CFRP
Carbon Fiber Reinforced Polymers (CFRP) are widely used in various industries due to their high strength-to-weight ratio and excellent mechanical properties. However, their susceptibility to damage under low-velocity impacts poses significant challenges. Understanding the impact behavior, damage mechanisms, and ways to enhance impact resistance is crucial for the safe and efficient use of CFRP materials.
Analytical Models for Low Velocity Impact
Analytical models play a vital role in predicting the behavior of CFRP under low-velocity impacts. A new model, building on Olsson's analytical framework, has been developed to estimate the critical load for delamination onset and approximate the load-displacement curve. This model incorporates stiffness degradation and has shown good agreement with experimental data, offering significant improvements over previous models.
Numerical and Experimental Approaches
Patch-Repaired CFRP Laminates
The low-velocity impact response of patch-repaired CFRP laminates has been studied using both numerical simulations and experimental tests. The damage development and failure processes were analyzed using continuum damage mechanics (CDM) and cohesive zone models (CZM). The results indicated that the numerical predictions closely matched the experimental measurements, and optimal patch parameters were identified to enhance impact resistance.
Aluminum Honeycomb Sandwich Structures
The impact behavior of aluminum honeycomb sandwich structures with CFRP face sheets was investigated. The study revealed that face sheet thickness significantly influences impact resistance, while cell wall thickness and honeycomb core height affect impact load and structural stiffness. Numerical simulations using a VUMAT subroutine provided insights into the progressive failure mechanisms, aligning well with experimental observations.
Woven CFRP Composites
Finite element models have been developed to predict the low-velocity impact and compression-after-impact (CAI) behavior of woven CFRP composites. The models were validated against experimental data, showing good agreement in force-displacement relations and failure modes. Microscopic damage analysis identified fiber breakage, matrix cracking, and delamination as key failure modes.
Geometrical Effects and Repeated Impacts
Specimen Geometry
The geometry of CFRP specimens significantly affects their impact response. Short thick targets tend to exhibit top surface contact failure, while long thin laminates show lower surface flexural failure. The energy-absorbing capability of the structure plays a crucial role in damage development and perforation thresholds.
Repeated Impacts
The response of CFRP plates to repeated low-velocity impacts has been studied using numerical models. The results indicated that impact time and peak force increase with sequential impacts, suggesting changes in laminate stiffness. Most intra-laminar and interlaminar damage occurs during the initial impacts.
High Fidelity Simulations and Impact Localization
High Fidelity Simulations
High fidelity finite element models have been developed to simulate the damage extent of CFRP laminates under low-velocity impacts. These models, validated against experimental data, accurately predict damage modes such as fiber damage, matrix cracks, and delamination. The numerical results closely match experimental observations, demonstrating the model's validity.
Impact Localization
An impact area localization system using fiber Bragg grating (FBG) sensors and an extreme learning machine (ELM) algorithm has been proposed. This system accurately identifies impact areas on CFRP plates, achieving a localization accuracy of 96.9%. Such systems are crucial for detecting invisible damage induced by low-velocity impacts.
Conclusion
The analysis of low-velocity impacts on CFRP materials involves a combination of analytical models, numerical simulations, and experimental validations. Understanding the influence of structural parameters, specimen geometry, and repeated impacts is essential for improving the impact resistance of CFRP composites. High fidelity simulations and advanced localization systems further enhance the ability to predict and detect impact damage, ensuring the safe and effective use of CFRP materials in various applications.
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