Buckling and crush resistance of high-density TRIP-steel and TRIP-matrix composite honeycombs to out-of-plane compressive load

Abstract

a b s t r a c tThe mechanical and structural responses of high-density TRIP steel and TRIP-steel/zirconia composite honeycomb structures were studied under uniaxial compression in the out-of-plane loading direction over a wide range of strain rates. Their mechanical response, buckling, and failure mechanisms differ considerably from those of conventional thin-walled, low-density cellular structures. Following the linear-elastic regime and the yield limit of the bulk material, the high-density square honeycombs exhibited a uniform increase in compression stress over an extended range of (stable) plastic deformation. This plastic pre-buckling stage with axial crushing of cell walls correlates with the uniaxial compressive response of the bulk specimens tested. The dominating material effects were the pronounced strain hardening of the austenitic steel matrix accompanied by a strain-induced a'-martensite nucleation (TRIP effect) and the strengthening effect due to the zirconia particle reinforcement. The onset of critical plastic bifurcation was initiated at high compressive loads governed by local or global cell wall deflections. After exceeding the compressive peak stress (maximum loading limit), the honeycombs underwent either a continuous post-buckling mode with a folding collapse (lower relative density) or a symmetric extensional collapse mode of the entire frame (high relative density). The densification strain and the post-buckling or plateau stress were determined by the energy efficiency method. Apart from relative density, the crush resistance and deformability of the honeycombs were highly influenced by the microstructure and damage evolution in the cell walls as well as the bulk material's strain-rate sensitivity. A significant increase in strain rate against quasi-static loading resulted in a measured enhancement of deformation temperature associated with material softening. As a consequence, the compressive peak stress and the plastic failure strain at the beginning of post-buckling showed an anomaly with respect to strain rate indicated by minimum values under medium loading-rate conditions. The development of the temperature gradient in the stable pre-buckling stage could be predicted well by a known constitutive model for quasi-adiabatic heating.

Microstructure and Deformation Response of TRIP-Steel Syntactic Foams to Quasi-Static and Dynamic Compressive Loads

“…The significant decrease of the strain hardening rate when exceeding a certain plastic deformation degree can be attributed to two factors: the quasi-adiabatic heating of the specimen due to the resulting deformation heat which remains to a great magnitude (~95%) in the steel matrix and the strain rate decline during the drop weight impact test. In agreement with previous findings [ 32 , 33 , 46 ], the deformation temperature in cellular austenitic stainless steel structures being subject to strain rates of 10 2 –10 3 s −1 can go up to 100 °C (or temperature gradient of ~80 K) or even higher when the failure is localized in shear bands [ 66 ]. Batches with higher density as the reference T0 exhibit higher deformation stresses and, hence, higher deformation work.…”

Multi-cell energy-absorbing structures with hollow columns inspired by the beetle elytra

“…Foam filled thin-walled structures also play an important role in the field of energy absorption due to the mechanical properties of the foam and the interaction between the foam and the confining shell [22][23][24]. Finite Elements have also been used to compare the mechanical characteristics and energy absorption efficiency of empty and foam filled tubes, with a general satisfactory agreement observed between simulations and experimental results [25][26][27]. A type of novel thin-walled structure inspired by the topology of the bamboo stem features a peculiar rib shape and number of ribs.…”

Mechanical properties of high-density TRIP steel honeycomb structures with varying cell profiles under different loading conditions

“…2. On the other hand, dynamic strain rates resulted in quasiadiabatic sample heating, which involved material softening [16]. Thus, the dynamic and static stress-strain curves intersected at elevated strains (Fig.…”