# Response Surface Optimization of Matched-Die Consolidation for BMI-Based CFRP Prepreg Laminates Toward Stiffened-Shell Manufacturing

## TL;DR

This paper optimizes the manufacturing process for BMI-based CFRP stiffened-shell structures to improve strength and reduce defects under extreme conditions.

## Contribution

A novel integrated manufacturing route and parameter optimization using response surface methodology for BMI-CFRP stiffened-shell structures.

## Key findings

- Tensile strength shows a unimodal dependence on processing parameters with B > D > A > C significance.
- Optimized conditions achieved a tensile strength of 2291 MPa with excellent agreement to predictions.
- Microstructural analysis showed tight bonding and void reduction under optimized conditions.

## Abstract

Hypersonic vehicles impose stringent requirements on lightweight structures to maintain mechanical integrity under extreme thermal environments. Bismaleimide (BMI)-based carbon fiber-reinforced polymer (CFRP) composites, featuring a high glass transition temperature and excellent thermal stability, are regarded as promising candidates for such applications. However, the high curing temperature and narrow processing window of BMI resins make it challenging to manufacture stiffened-shell structures with low defect levels and high fiber volume fractions. In this study, an integrated manufacturing route—hot-melt prepregging–filament winding–matched-metal mold forming—is proposed, and the key processing parameters are optimized via single-factor experiments and the Box–Behnken response surface methodology. The tensile strength of the laminate is selected as the response variable to evaluate the effects of the compression displacement (A), thermal consolidation/bonding temperature (B), heating rate (C), and cooling rate (D). The results reveal a unimodal dependence of the tensile strength on each parameter, with the significance ranking B > D > A > C; moreover, the A–B and A–D interactions are significant (p < 0.01). The established quadratic regression model exhibits good agreement with experimental data (R2 = 0.974; R2_adj = 0.949). The predicted optimum conditions are A = 0.07 mm, B = 114.93 °C, C = 1.35 °C·min−1, and D = 4.58 °C·min−1, corresponding to a predicted tensile strength of approximately 2287 MPa. Validation experiments yielded 2291 MPa, in excellent agreement with the prediction. Microstructural observations indicate tight interlaminar bonding and a pronounced reduction in voids under the optimized conditions. Applying the optimized process to fabricate stiffened-shell demonstrators achieves a fiber volume fraction of >60% and a void content of <1%. This work provides a quantitatively defined processing window and parameter optimization basis for the high-quality manufacturing of BMI-CFRP stiffened-shell structures, with significant engineering relevance.