Mechanical behavior and design optimization of composite and hybrid metal-composite drill pipes under combined loading conditions

This study presents a comprehensive investigation into the mechanical behavior of drill pipes under combined loading conditions, with particular focus on the complex interactions between structural configuration and multi-axial loading states. A three-dimensional elastic model is developed and validated through finite element analysis to predict stress distributions and failure mechanisms in both composite and hybrid metal-composite drill pipes subjected to simultaneous torsion, pressure, and axial load . Analysis reveals unprecedented dual-peak phenomena in axial load capacity, occurring at specific combinations of winding angles, demonstrating complex interactions between fiber orientation and combined loading. Under combined loading conditions, optimal winding angles vary significantly: 60 ° - 80 ° for internal pressure dominance, approximately 60 ° for torsional loading, and combinations of low ( 0 ° - 10 ° ) and high ( 55 ° - 75 ° ) angles for maximum axial capacity . The study establishes that optimized composite configurations can achieve load-bearing capabilities comparable to traditional metallic pipes while offering a tenfold increase in specific strength . These findings provide crucial guidelines for drill pipe design optimization, particularly significant for challenging drilling environments where the balance between structural performance and weight reduction becomes critical. The theoretical framework and design insights developed in this study contribute to advancing the fundamental understanding of multilayered structures under complex loading conditions. • A 3D elastic model captures complex stress in composite and hybrid drill pipes under combined loads. • Dual-peak in axial load capacity reveals interactions between fiber orientation and multi-axial loads. • Optimal winding angles vary: 60°-80° for pressure, ∼60° for torsion, and specific low-high angles for max axial load. • Optimized composite drill pipes match metallic ones in load-bearing, with 10x specific strength gain. • Metal core thickness in hybrids is crucial for balancing performance and weight.