Finite Element Analysis on the Unloading Elastic Modulus of Aluminum Foams by Unit-cell Model
This paper presents finite element analyses (FEA) on the unloading elastic moduli of aluminum foams under uniaxial loading and bending conditions. The unit-cell model of Gibson and Ashby was utilized in the FEA with elasto-perfectly plastic material. Compression, tension, and bending tests simulations were carried out using Abaqus software. The non-linearity effect caused by structural imperfection/buckling of unit-cell was incorporated. From the compressive test simulation, it was confirmed that the results showed good agreement with the referred experimental data. This means that the developed FE model can be regarded as an RVE model of aluminum foams. Then, the deformation characteristic and elastic modulus obtained from all simulations were compared and examined. As the results, the elastic modulus obtained from bending test demonstrated higher value than that of under uniaxial loads. This discrepancy increases gradually as the relative density decreases. The mechanism responsible for generating the discrepancy in stiffness was discussed. Furthermore, this work points out the necessity of measuring both Young’s and flexural moduli for designing an engineering structure using foam materials especially when accuracy and precision are demanded.
Experimental investigation of shear stress effect on the flexural behavior of aluminum foam beam
We conducted an experimental investigation on the flexural behavior of closed-cell aluminum foam beam under shear stress effect. Three-point bending and flexural vibration tests were carried out and the shear stress effect was generated by changing the specimen’s length. From the bending test, the measured deflection was used to quantify the flexural modulus. From the vibration test, the measured natural frequencies of flexural vibration mode were used to calculate the flexural modulus. The results show that the flexural moduli obtained from both tests agree well. Then, the flexural modulus value was compared with the theoretical value estimated by Timoshenko’s beam theory. As a result, the experimental value was found to be much smaller than the theoretical value when shear stress effect is dominant. Does this mean Timoshenko’s theory cannot describe the flexural behavior of aluminum foam beam? How to fit Timoshenko’s theory with the experimental data is discussed. Moreover, the reason why the flexural modulus was remarkably degraded under shear effect is elaborated.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.