Experimental Study on Internal Explosion Tearing of Circular Steel Tubes

Literature Overview

The paper by Wang Debao, Ma Honghao, Shen Zhaowu, and Lin Moujin from the University of Science and Technology of China (2013) presents an experimental investigation on the structural response of circular steel tubes subjected to internal explosion loading. The study was supported by the National Natural Science Foundation of China (Key Project 51134012 and General Program 51174183). The research aims to understand the mechanisms of steel tube tearing under internal explosion and to provide reference for the theoretical and practical aspects of steel tube demolition by blasting.

Experimental Setup and Parameters

The experimental setup involves two key components: the internal explosion charge and the test steel tube. The following table summarizes the key parameters:

The internal explosion charge is a custom-made circular tube with grooves on the outer surface. The grooves serve as constraint weak zones to direct the tearing of the test steel tube. The test steel tube is either filled with water or air to serve as the pressure transmission medium.

Key Findings and Technical Interpretation

The experimental results reveal several important findings regarding the internal explosion tearing of circular steel tubes:

1. Shock wave dominance: The primary force responsible for tearing the steel tube is the explosion shock wave rather than the fragments from the internal explosion charge casing. This is a significant finding because it suggests that the tearing mechanism is primarily driven by the pressure wave generated by the explosion, rather than by mechanical impact from flying fragments.
2. Pressure medium effect: Using water as the pressure transmission medium produces significantly better tearing results compared to air. This is attributed to the higher density and incompressibility of water, which more effectively transmits the shock wave energy to the steel tube wall.
3. Groove effect: Pre-cutting grooves on the outer surface of the internal explosion charge casing, serving as constraint weak zones, enables directional tearing of the test steel tube. This is a critical finding for controlled demolition applications, as it allows for precise control over the tearing location and pattern.
4. Parameter influence: The study systematically investigates the effects of explosive charge quantity, pressure medium, number of grooves on the internal explosion charge casing, and charge length on the test results. Each parameter has a distinct influence on the tearing behavior, and the optimal combination of parameters is identified for effective tearing.

Engineering Practice Implications

The findings of this study have direct applications in the field of controlled demolition of steel structures:

1. Controlled demolition design: The study provides a basis for the design of controlled demolition operations for circular steel tubes. The use of pre-cut grooves on the internal explosion charge casing enables precise control over the tearing location, which is essential for safe and efficient demolition.
2. Explosive charge optimization: The systematic investigation of explosive charge quantity and configuration provides guidelines for optimizing the charge design to achieve the desired tearing effect with minimal explosive usage.
3. Pressure medium selection: The superior performance of water as a pressure transmission medium suggests that water-filled configurations should be preferred for internal explosion demolition of steel tubes.
4. Safety considerations: The understanding of the tearing mechanism, particularly the dominance of shock wave over fragment impact, has implications for safety planning during demolition operations. The shock wave propagation and its effects on surrounding structures must be considered in the safety assessment.
5. Structural assessment: The study provides data on the structural response of steel tubes under internal explosion loading, which can be used for the assessment of existing structures and the design of protective measures.

Key Questions and Reflections

Several questions arise from this study that warrant further investigation. First, the study focuses on 45# steel tubes, but the tearing behavior may differ for other steel grades, particularly high-strength steels or stainless steels. The material properties, including yield strength, ultimate tensile strength, and ductility, may significantly influence the tearing mechanism and the optimal charge design.

Second, the study does not address the effects of tube geometry beyond the circular cross-section. The tearing behavior of rectangular, oval, or other non-circular cross-sections may differ significantly, and additional research is needed to extend the findings to these geometries.

Third, the study does not discuss the residual deformation and fracture characteristics of the torn steel tube in detail. The fracture surface morphology, crack propagation pattern, and residual stress distribution in the torn tube are important for understanding the tearing mechanism and for predicting the behavior of similar structures under explosion loading.

Summary

This study provides valuable experimental data on the internal explosion tearing of circular steel tubes, with clear findings on the dominance of shock wave over fragment impact, the superior performance of water as a pressure medium, and the effectiveness of pre-cut grooves for directional tearing. The results are directly applicable to controlled demolition design, with practical guidelines for explosive charge optimization and pressure medium selection. Engineers involved in steel structure demolition should consider these findings when designing controlled demolition operations to ensure safety, efficiency, and precision.