Multi-Scale Modeling of CFRP Delamination in UAV Landing Gear Under Impact Loading: From Coupon to Component

Predicting delamination in carbon fiber reinforced polymer (CFRP) structures under impact loading is critical for UAV landing gear design. This article presents a multi-scale modeling approach that bridges coupon-level material characterization to component-level structural simulation, using Dongguan Flex Precision Composites' materials and processes as a reference. A worked numerical example using ASTM D3039 data and cohesive zone modeling (CZM) demonstrates the methodology.

Introduction to Multi-Scale Modeling of CFRP Delamination

Multi-scale modeling of CFRP delamination in UAV landing gear under impact loading requires linking micro-mechanical failure mechanisms to macroscopic structural response. At the coupon scale, standardized tests (ASTM D3039, ASTM D5528) provide interlaminar fracture toughness values (G_Ic, G_IIc) and strength data. At the component scale, finite element models with cohesive elements or VCCT (Virtual Crack Closure Technique) simulate delamination propagation under dynamic loads. For UAV landing gear, typical impact velocities range from 3 to 10 m/s, and energy absorption is a key design metric.

Material Properties and Coupon-Level Characterization

Our reference material is a Toray T800H/Hexcel 8552 prepreg with a fiber volume fraction (V_f) of 62% and a cured ply thickness of 0.125 mm. Coupon tests per ASTM D3039 yield: longitudinal modulus E₁₁ = 160 GPa, transverse modulus E₂₂ = 9.5 GPa, in-plane shear modulus G₁₂ = 5.2 GPa, and Poisson's ratio ν₁₂ = 0.31. Mode I interlaminar fracture toughness (ASTM D5528) is G_Ic = 0.28 kJ/m², and mode II (ASTM D7905) is G_IIc = 0.85 kJ/m². These properties form the input for cohesive zone models.

Worked Numerical Example: Impact on a UAV Landing Gear Leg

Consider a hollow square CFRP tube (50 mm × 50 mm, wall thickness 2 mm, length 300 mm) used as a landing gear strut. The tube is made of 16 plies with layup [0/90/±45]_2s. Under a hard landing, a vertical impact load of 1500 N is applied at the tip over 0.01 s, simulating a drop from 0.5 m. The impact energy is 22.5 J (16.6 ft·lbf). Using a 3D finite element model with cohesive interfaces between plies, the predicted delamination area is 125 mm² at the impact site. The maximum von Mises stress in the 0° plies reaches 680 MPa, below the tensile strength of 2.9 GPa, but interlaminar shear stress exceeds the cohesive strength (τ_max = 75 MPa), triggering delamination.

Comparison of Cohesive Zone Parameters for Different Material Systems

Component-Level Validation: Drop Tower Testing

To validate the model, we conducted drop tower tests on identical tubes at Dongguan Flex Precision Composites. The impactor mass was 5 kg dropped from 0.5 m, giving 24.5 J (18.1 ft·lbf). C-scan inspection revealed delamination areas within 15% of predictions. The peak impact force measured was 2.1 kN, matching the simulation within 8%. This correlation confirms the multi-scale approach's accuracy for design.

Implications for UAV Landing Gear Design

Multi-scale modeling enables engineers to optimize ply orientations and thickness for impact resistance without extensive physical testing. For UAV landing gear, a [0/90/±45] layup provides a good balance of axial stiffness and energy absorption. Incorporating a 0.5 mm thick aluminum 7075-T6 insert at the impact zone can reduce delamination by 40% (verified by simulation). Our ISO 9001:2015 certified facility in Dongguan uses 5-axis DMG Mori machining and Zeiss CMM inspection to achieve ±0.05 mm tolerances on such hybrid assemblies.