Study On Damping Property Of Aluminum Foam With Biomimetic Porous Structure

The powered exoskeleton is a wearable mobile machine powered by a system of electric motors that assists physical movement with enhanced strength and endurance,and have a wide range of applications in the military,industry,medical assistance and rehabilitation.But,the electric motors in powered exoskeleton produce a vibration that is transmitted to the operator’s body and hand,and prolonged exposure to vibration can cause injuries known as Hand-Arm Vibration Syndrome.Due to its metal characteristics and porous structure,aluminum foam has excellent energy absorption and mechanical strength,and can be used as a vibration reduction material under complex working conditions in powered exoskeleton.In this study,the determination of damping of aluminum foam has been analyzed and the potential application of aluminum foam in vibration reduction composite structure of power exoskeleton were preliminarily analyzed.The main research contents are as follows:(1)Based on the elastic strain energy and plastic dissipation energy variation of the porous structure during vibration,a simulation method of loss factor calculation is proposed.A threedimensional porous structure model was reconstructed from the CT data,and porous structure parameters such as porosity,average pore size and local thickness were calculated.The three-point bending vibration loading of a porous structure was simulated and the distribution of the elastic and plastic energy of the structure was obtained.On this basis,amplitude dependent loss factor was calculated and the results are in accordance with the experimental results in literature.The stress distribution inside the porous structure showed that when the porous structure is in elastic deformation stage,the area around the pores will deform plastically in advance,dissipate energy and cause a damping effect,indicating that micro-plastic deformation damping is an important mechanism affecting the damping performance of porous structure.(2)The damping properties and mechanical behavior of the biomimetic porous structure under three-point bending and uniaxial compression vibration loading were investigated.Three sets of aluminum foam samples with different sizes and pore structure parameters were prepared and the damping performance of the porous material was investigated by a combination of vibration experiments and finite element simulations.The results showed that the loss factor of three-point bending loading is about 43% higher than that of uniaxial loading due to the complex stress state inside the porous structure.During three-point bending loading,the damping property of the porous structure is enhanced as the thickness of the model increases due to the change in the state of force.During uniaxial loading,the loss factors of different height models are almost the same due to the force state being an overall compression.The pore structure parameters can affect the stress distribution in the porous structure,which consequently influence the damping performance.In the porosity range of 79% to 83%,the damping property of the porous structure is almost independent of the porosity.As the average pore size decreases,it intensifies the difference in elastic modulus between the matrix and the pores,enhancing the damping properties of the porous structure.(3)The damping property of porous composite structure and its potential for application in powered exoskeletons were investigated.Based on the cancellous/cortical bone composite structure,two simplistic biomimetic porous composite structures,a filled circular tube and a sandwich layers,were designed.The study showed that the interaction between the porous material and the metallic material significantly enhances the damping properties and mechanical strength of the composite structure.In view of the working conditions of riveting tool and human upper limb configuration,a porous composite structure of aluminum alloy round tubes filled with aluminum foam was designed.The vibration simulation results showed that the porous material enhances the mechanical strength and damping properties of the structural material and reduces the amplitude of vibrations in the structure by approximately 46.2%.In addition to this,vibration simulations were carried out on circular tubes filled with aluminum foam of different thicknesses.The results show that increasing the thickness of the porous material can improve the damping performance of the structure,but there is a marginal diminishing effect on the improvement.Therefore,the relationship between weight and damping performance needs to be balanced in the design of the structure.