Honeycomb Steel Tube Confined Concrete Target Against Multiple Projectile Impact

Literature Overview

The paper by Song Dianyi, Tan Qinghua, Shen Zhiqiang, and Jiang Zhigang from the National University of Defense Technology investigates the anti-penetration performance of honeycomb steel tube confined concrete (STCC) targets under multiple projectile impacts. Published in the journal Vibration and Shock (Vol. 40, No. 10, 2021, pp. 133-139), this study addresses a critical engineering need in protective structure design, particularly for blast and ballistic resistance applications. The research is funded by the Hunan Provincial Natural Science Foundation (2018JJ2470).

Core Technical Content

The study compares the performance of honeycomb steel tube confined concrete targets against semi-infinite concrete targets under multiple 12.7 mm armor-piercing projectile impacts. The honeycomb configuration divides the concrete into discrete cells, each confined by the steel tube walls, creating a modular damage containment system.

Key Findings and Damage Modes

The core concrete within the honeycomb cells exhibits a characteristic damage pattern described as "funnel crater + penetration tunnel + lateral cracks." This damage mode is fundamentally different from that observed in conventional confined concrete targets, where damage propagates freely beyond the immediate impact zone.

Impact Count	DOP Reduction vs. Semi-infinite	Funnel Volume Reduction	Funnel Depth Reduction
4 impacts	~18%	—	—
6 impacts	—	~78%	~55%

The equivalent penetration resistance of the honeycomb STCC target was calculated based on measured damage parameters including funnel crater volume and depth. The results demonstrate that the honeycomb steel tube effectively confines concrete damage within the struck cell, preventing damage propagation to adjacent cells.

Technical Analysis from a Steel Pipe and Welding Perspective

Steel Tube Design Considerations

From a steel pipe manufacturing standpoint, the honeycomb configuration requires precise fabrication of rectangular or polygonal steel tube sections with uniform wall thickness. The key design parameters include:

Wall thickness: Must be sufficient to confine the concrete without rupturing under high-strain-rate loading
Cell dimensions: Determined by the balance between damage containment effectiveness and overall structural weight
Material grade: Typically high-strength structural steel (Q345 or equivalent) to withstand dynamic loading

Welding Process Implications

The fabrication of honeycomb steel tubes involves multiple transverse and longitudinal welds. From a welding engineering perspective, the following considerations are critical:

Weld joint quality: Any weld defects such as incomplete fusion, porosity, or undercut could serve as crack initiation sites under dynamic loading conditions
Heat-affected zone (HAZ) properties: The microstructural changes in the HAZ must be controlled to maintain adequate toughness at room temperature and low temperatures
Residual stress management: Multi-pass welding of the honeycomb geometry introduces complex residual stress states that could influence structural response under impact

Connection with Standards

The steel tube fabrication would typically reference standards such as GB/T 3091 (welded steel tubes for general purposes) or API 5L for pipeline applications. The welding procedures should comply with NB/T 47014 or ASME Section IX qualification requirements. Non-destructive testing (NDT) of welds should include UT or MT for longitudinal seams and PT for transverse welds, following relevant acceptance criteria.

Engineering Practice Integration

Application Scenarios

The honeycomb STCC concept has direct applications in:

Military protective structures (blast walls, ammunition bunkers)
Civil infrastructure protection (bridge piers, tunnel portals)
Industrial facility hardening against vehicle-borne threats

FMEA Analysis of Potential Failure Modes

Applying Failure Mode and Effects Analysis (FMEA) to the honeycomb STCC system:

Failure Mode	Cause	Effect	Severity	Detection Method
Weld rupture	Defective weld, HAZ embrittlement	Loss of confinement, concrete spalling	High	UT, MT inspection
Cell wall buckling	Insufficient wall thickness	Reduced confinement pressure	Medium	Finite element analysis, load testing
Concrete cover spalling	Excessive dynamic pressure	Reduced structural integrity	High	Visual inspection, rebound hammer
Inter-cell damage propagation	Poor cell wall design	Cascading failure	Critical	Full-scale impact testing

Study Insights and Reflections

This research represents a significant advancement in the understanding of confined concrete behavior under repeated ballistic loading. The honeycomb configuration effectively transforms what would be a catastrophic multi-impact failure scenario into a series of localized, manageable damage events. The 78% reduction in funnel volume after 6 impacts is particularly remarkable, suggesting that the energy absorption mechanism is fundamentally different from conventional confined concrete.

From a practical fabrication standpoint, the key challenge lies in ensuring consistent weld quality throughout the honeycomb geometry. The numerous weld intersections create complex stress concentrations that are difficult to inspect and even more difficult to qualify. Engineers should consider using full-penetration butt welds with backing bars for all structural connections, and implement 100% UT coverage on critical welds.

The research opens important questions for further investigation: How does the steel tube material grade affect performance? What is the optimal cell geometry (square, hexagonal, triangular)? How does the concrete strength grade interact with the steel tube confinement? These questions warrant additional experimental and numerical studies to establish comprehensive design guidelines.

This study provides a solid foundation for the development of next-generation protective structures that combine the cost-effectiveness of concrete with the damage containment capability of steel tube confinement in a modular honeycomb configuration.