Papers by Author: Long Mao Zhao

Abstract: The deformation/failure modes and dynamic response of fully clamped cylindrical sandwich shells with aluminum foam cores subjected to air blast loading were investigated experimentally. A four-cable ballistic pendulum system was employed to measure the impulse imparted to the blast-loaded specimen. The deformation/failure modes of specimens were classified and analyzed, the effects of face-sheet thickness, core relative density, specimen curvature and mass of charge on the structural response of metallic sandwich shells were examined. Experimental results indicate that both the deformation/failure modes and the dynamic response of the sandwich shells are sensitive to the structural configurations and blast impulse. The experimental results are useful for validating theoretical predictions, as well as in engineering applications of cellular metal sandwich structures.

Abstract: In this paper the structure response of quasi-statically loaded sandwich beams made of aluminum skins with open-cell aluminum foam cores is investigated experimentally. The experimental programme was designed to investigate the deformation and failure modes of sandwich beams, so a large number of experiments have been conducted, and the experimental results are reported and discussed systematically. It is found that sandwich beams under quasi-static punching loads can fail in several modes: face yield, face wrinkling, core shear, the bottom face fracture and interfacial failure between the core and the faces. Moreover, the effects of face thickness, cell size of foam material on the failure and deformation modes were discussed. The experimental results are of worth to optimum design of cellular metallic sandwich structures.

Abstract: In our city, 75000 m3 Wet Gasholder generated coal gas leak during the work due to the crack of tower wall , which directly endangered life and property security of the people. In the paper, the cause on the failure of gasholder was made much conjecture. Firstly, physicochemical examination and mechanics property on gasholder material component were conducted. Weld conditions between pillar and joist were observed on spot. Secondly, stress of gasholder was analyzed by using finite element code. Thirdly, field tests on the vibration of gasholder were also carried out by means of vibration apparatus. Finally, the principal cause of the failure is determined, and some propose on the maintenance and construction of gasholder is provided.

Abstract: This paper presents a study of heat treatment on the quasi-static and dynamic compressive properties of the open cell aluminum alloy foams in as-fabricated (F), age-hardened (A) and T6-strengthened (T6) conditions. Although the strain rate and heat treatment of foams are different, all exhibit similar deformation behavior in the subsequent deformation. The yield stress of foams at different strain rates are improved by heat treatment, all exhibit some strain rate sensitivity. However, the densification strain of foams is not sensitive to heat treatment.

Abstract: The static and dynamic compressive behaviors of open-cell aluminum alloy foams with virtually the same relative density of 0.4 were investigated. The foams have different cell sizes (0.5mm, 1.5mm, 2.5mm) but similar cell morphology and microstructure. The yield strength of these foams was characterized as a function of strain rate and cell morphology. The experimental results indicated that the mechanical responses of foams are sensitive to strain rate, and dependent of the cell size. The present results are compared in details with recent findings obtained from the aluminum foams.

Abstract: The dynamic buckling caused by propagation of a stress wave in single-wall carbon nanotube subjected to impact torque is investigated. The single-wall carbon nanotube is modeled by a cylindrical shell with semi-infinite length, and the dynamic buckling under impact torque is reduced to a bifurcation problem caused by the propagation of torsion stress wave. The bifurcation problem can be converted to solving a group of nonlinear algebraic equations. The numerical computation is carried out, and the effects of the different parameters on dynamic buckling are discussed. It is found that if critical buckling time of the carbon nanotube is different, the corresponding buckling model is different, too. Relation between the critical buckling stress and the critical buckling time is given. Molecular-dynamic simulations of torsional deformation of a single-wall carbon nanotube have been used to obtain the critical buckling strain, which is 0.064. In this work, the critical buckling strain obtained by the continuum model is 0.061, which is very close to the value 0.064. Single-wall carbon nanotubes have very much powerful anti-impact torque, and the critical buckling shearing stress can reach up to 132GPa.

Abstract: The dynamic compressive behavior of open-cell aluminum alloy foams with different length of specimens was investigated using the split Hopkinson pressure bar technique. Plastic strength was measured for aluminum alloy foam specimens having the three cell sizes but similar cell microstructure. Longer specimens exhibited lower mean strength and broader scattering of the strength values than the shorter ones. It can be observed that mechanical response of aluminum alloy foams appear to be dependent of the cell size for both the shorter and longer specimens.

Abstract: The compressive deformation behavior of open-cell aluminum foams with different densities and morphologies was assessed under quasi-static and dynamic loading conditions. High strain rate experiments were conducted using a split Hopkinson pressure bar technique at strain rates ranging from 500 to 1 2000 − s . The experimental results shown that the compressive stress-strain curves of aluminum foams also have the “ three regions” character appeared in general foam materials, namely elastic region, collapse region and densification regions. It is found that density is the primary variable characterizing the modulus and yield strength of foams and the cell appears to have a negligible effect on the strength of foams. It also is found that yield strength and energy absorption is almost insensitive to strain rate and deformation is spatially uniform for the open-celled aluminum foams, over a wide range of strain rates.