Proactive regulation of axial crushing behavior of thin-walled circular tube by gradient grooves

• Gradient grooves are preset along the thin-walled circular tube to proactively regulate the collapse process.
• The sectionalized theory is developed to predict the quadratic upward crushing force.
• It is systemically studied the effects of non-dimensional defect parameters on buckling mode and crushing force of gradient grooved tube (GGT).
• It is demonstrated that GGT has a better stability than perfect tube when used as an absorber to protect the graphite in HTR from free-fall control rob.

The progressive buckling behavior of a gradient grooved tube (GGT) designed for high temperature gas cooled reactor (HTR) is systematically studied in this paper. Based on the plastic hinge formation process, a sectionalized theoretical model is established to predict the quadratic upward trend of crushing force of GGT. The ordered and stable energy absorbing process of GGT is examined by low-speed axial impact using drop hammer test machine. The effect of proactive regulation parameters, including non-dimensional groove width W/(h0+h)W/(h0+h), groove depth h0/hh0/h and half wavelength (H+W−h)/Dh on buckling modes and force–displacement curve is determined by experiments and FE simulation. The non-dimensional groove width W/(h+h0) is determined as π/2π/2 according to the geometry coordination of bending grooves. The non-dimensional groove depth h0/h   influences local buckling behavior and the critical value 0.6 for regular bending has been determined by numerical simulation. The quadratic trend force–displacement curves of GGT can be actively controlled by (H+W−h)/Dh within a certain range less than 1.2. Free-fall impact experiments show that GGT has a better stability than perfect tube when used as an energy absorber to protect the graphite in HTR from slender control rod impact.