Modeling of Local Mesoscale Interactions in Metal-Composite Joints Based on 3D Anchors Matrix

Fikret Enes Altunok Smart Structures and Systems Lab Politecnico di Torino, Torino, Italy [email protected] Modeling of Local Mesoscale Interactions in Metal-Composite Joints Based on 3D Anchors Matrix 13/11/2025 ICCS27 27th International Conference on Composite Structures 3-6 September 2024 –Ravenna, Italy Francesco Quarta Politecnico di Torino, Torino, Italy [email protected] Prof. Giorgio De Pasquale Smart Structures and Systems Lab Politecnico di Torino, Torino, Italy [email protected] Anchors CFRP Stack #1 CFRP Stack #2 1. Introduction 13/11/2025 ICCS27 - 27th International Conference on Composite Structures –Ravenna, Italy 1 Motivation: »Lightweighting is critical for efficiency, fuel savings, and sustainability in aerospace, automotive, construction, and other sectors. Reduces operational costs and environmental impact by minimizing material usage and weight. Challenges in Joining Dissimilar Materials: »Traditional methods like adhesive bonding and mechanical fastening face limitations. »Adhesive bonding can introduce weight and may degrade over time, impacting long-term reliability. »Mechanical fastening (e.g., bolts, rivets) requires drilling, which can weaken materials, especially composites. »Both methods add complexity, cost, and potential points of failure in the assembly process. Innovative Metal-Composite Joining Technique (MIMOSA Joint): » Utilizes metal additive manufacturing to create "anchors" on the metal surface. » These anchors interlock mechanically with the composite, mimicking the function of traditional fasteners without their drawbacks. » Aims to simplify the joining process, reduce manufacturing costs, and enhance joint durability across various applications. » Potential to revolutionize how lightweight structures are assembled, offering stronger, more reliable joints. » Scalable to different sizes and materials, making it adaptable to various industrial needs. www.mimosaproject.eu 2. Model Description Simulation Approach 1: Modelling Individual Layers with Homogenized CFRP Orthotropic Properties: »CFRP adherend treated as a composite material made by layers with homogenized orthotropic properties. »Simplifies modeling by averaging the directional properties across the entire structure. Forcing the fiber directions to follow the translation caused by the anchor. »Uses Puck failure theory to predict failure of the fibers. »Cohesive Zone Modeling (CZM) applied at the metal-matrix interface to simulate debonding and progressive damage. Simulation Approach 2: Detailed Fiber Tows Incorporated into Model: »Incorporates individual fiber tows within the CFRP adherend for a more detailed analysis. »Focuses on critical layers near the anchors where stress concentrations are highest. »Other than the metal-matrix interface, Cohesive Zone Modeling (CZM) applied at the fibermatrix interface as well to capture fiber decohesion and its potential effects at failure. »Provides a more accurate representation of how the joint behaves under load, particularly in high-stress layers. Model Simulation Approach 1 Fully Bonded Interface Damage Simulation Approach 2 Fully Bonded Interface Damage Sim#1 Sim#2 Sim#1 Sim#2 13/11/2025 ICCS27 - 27th International Conference on Composite Structures –Ravenna, Italy 2 RVE Creation for Simulation Approach 1: »CFRP adherend created from individual sheet body layers and resin-rich regions. »Mesh refinement around critical areas, especially near the anchors, to accurately simulate stress distributions. »Ensures that the modeled fiber directions follow the anchor-induced translations, providing a realistic simulation of the joint's behavior. RVE Creation for Simulation Approach 2: »RVE includes detailed modeling of individual fiber tows, resin-rich regions, and fiber-matrix interfaces. »CZM applied not only at the metal-matrix interface but also at the fiber-matrix interface to model potential decohesion. 2. Model Description Approach 1 Imposed fiber orientations Metal adherend Resin rich regions CFRP adherend 0oLayer 90oLayer CFRP layers Full RVE Approach 2 10mm Imposed orientations for fiber tows Metal adherend 0oLayer 90oLayer CFRP adherend Resin rich regions Fiber tows Metal-matrix interface Fiber-matrix interface 13/11/2025 ICCS27 - 27th International Conference on Composite Structures –Ravenna, Italy 3 3. Sample Preparation and Fabrication Advanced Fabrication Techniques: Additive Manufacturing and Layup Process: »Metal adherend fabricated using additive manufacturing (laser-based bed fusion –LBPF-) with AlSi10Mg alloy. Composite adherend created by stacking prepreg layers of carbon fiber-reinforced polymer (CFRP).The composite is applied directly onto the anchor-modified metal surface, ensuring precise alignment. Autoclave curing used to enhance the mechanical properties and ensure a strong bond between the metal and composite. Validation of the RVE: Microscopic Inspection and Layer-by-Layer Analysis: »Microscopic inspection conducted to assess the quality of the joint, particularly around the anchors. Cross-sectional analysis to observe fiber translation, resin-rich regions, and potential defects. Focus on validating the RVE by comparing observed microstructures with simulated results. Ensures that the physical samples accurately represent the conditions modeled in the RVE. Sample preparation and microscopic images from different sections. 13/11/2025 ICCS27 - 27th International Conference on Composite Structures –Ravenna, Italy 4 4. Modeling Results Simulation of Anchored Joints; Predicting Behavior Under Load: »Simulations conducted to assess how the anchored joints distribute load across the composite and metal adherends. »Analysis of stress distribution patterns, particularly around the anchors, to understand load transfer mechanisms. »Comparisons made between the two simulation approaches to evaluate the impact of fiber modeling on load-bearing capacity. Trimetric sectioned view Side view 0 degree layer 90 degree layer 13/11/2025 ICCS27 - 27th International Conference on Composite Structures –Ravenna, Italy 5 Critical Stress Points: »Analysis of stress distributions across the different simulation approaches. »Simulation Approach 1 (Homogenized CFRP Layers): More uniform stress distribution across the 0-degree layers. »Simulation Approach 2 (Detailed Fiber Tows): Stress concentrations observed near the anchor and along the fiber-matrix interfaces. »Higher stress levels in translated fibers in Simulation Approach 2, particularly on the -X side of the anchor. »Comparison of how fiber orientation and layer modeling affect stress distribution and potential failure zones. 4. Modeling Results Layer 2 1% 3% 5% Strain Layer 3 Side View Sim#1 Sim#2 Sim#1 Sim#2 Sim#1 Sim#2 Approach 1 Layer 2 Layer 3 Side View Sim#1 Sim#2 Sim#1 Sim#2 Sim#1 Sim#2 Approach 2 13/11/2025 ICCS27 - 27th International Conference on Composite Structures –Ravenna, Italy 6 +X Layer 2: 0 degree layer, Layer3: 90 degree layer Fiber Failure Prediction: »Comparison of fiber failure between the two simulation approaches. »Simulation Approach 1 (Homogenized CFRP Layers): Fiber failure more uniformly distributed due to the homogenized nature of the layers. Failure tends to initiate at regions with high stress concentrations around the anchor edges. »Simulation Approach 2 (Detailed Fiber Tows): Localized fiber failure more prevalent due to detailed modeling of individual tows. Higher sensitivity to fiber orientation and placement, with failure often initiating at the fiber-matrix interfaces. »Impact of fiber translations and debonding in Simulation Approach 2 leads to earlier and more localized failure compared to Simulation Approach 1. 4. Modeling Results Layer 2 1% 3% 5% Strain Layer 3 Side View Sim#1 Sim#2 Sim#1 Sim#2 Sim#1 Sim#2 Approach 1 Layer 2 Layer 3 Side View Sim#1 Sim#2 Sim#1 Sim#2 Sim#1 Sim#2 Approach 2 13/11/2025 ICCS27 - 27th International Conference on Composite Structures –Ravenna, Italy 7 +X Layer 2: 0 degree layer, Layer3: 90 degree layer 5. Additional Critical Modeling Results Early Damage Initiation in Resin-Rich Regions: »Failure in resin-rich regions begins at strain levels as low as 0.5%. These regions are particularly vulnerable due to the presence of air pockets and inadequate fiber reinforcement. Early damage here significantly reduces the joint’s overall load-carrying capacity. Metal Adherend Failure Considerations: »Metal adherends experience early damage initiation, similar to resin-rich regions. Failure typically starts near the anchor base, where stress concentrations are highest. This early onset of failure in metal components can lead to a significant reduction in the joint's structural integrity. 0.5% 1% 2% Strain Sim#1 Sim#2 Sim#1 Sim#2 Approach 1 Resin Failure Metal Failure 13/11/2025 ICCS27 - 27th International Conference on Composite Structures –Ravenna, Italy 8