Papers by Keyword: Smart Composite

Abstract: The single crystal Ni-Mn-Ga and Ni-Mn-Ga particulate composites have responded to mechanical stress up to 1 kHz frequencies with significant acoustic attenuation. It has been observed that in Ni-Mn-Ga polymer composites, a heavy static load on both the ends of the system increases the acoustic stress amplitude and appears to have acoustic loss drops. The attenuation, as a function of frequency shows resonances in the displacement of the vibrating particle indicating the twin boundary motions. It is inferred that the resonances beyond the principal mode are highly damped in the Ni-Mn-Ga composite samples.

Abstract: NiMnGa alloys are attractive for the magnetic induced shape memory effect, especially as promising functional elements in smart composite materials and structures. Recently, more attentions are put on NiMnGa composite materials. In this paper, NiMnGa particles have been dispersed and oriented in a polymer matrix with high content under magnetic field. The damping behavior of NiMnGa/polymer composites was investigated in by DMA, contrasting to the pure polymer.

Abstract: Smart composite material-MRF’s rheological properties such as viscosity and shear modulus can vary when subjected to different magnetic fields. This paper established the vibration model of the smart composite beam featuring MRF. The vibration analysis was finished under different magnetic field strengths using the method of complex stiffness. The experiment was performed to validate the theoretical predicted vibration responses. From both studies, the natural frequencies and loss factors of the MRF beam were shifted to a higher lever when the applied magnetic field increases. From the findings of the analysis, it is observed that MRF presents vibration control capabilities.

Abstract: A new type of smart composite developed in our group was studied in terms of shape memory behavior. The smart composites were composed of NiMnGa ferromagnetic shape memory alloy particles (FSMAP) and a polymer matrix, where NiMnGa FSMAP will bring shape memory effect and the matrix polymer enhances ductility. Two kinds of NiMnGa were selected by taking the phase constitution into account (parent or martensite state at room temperature). The shape memory properties are reported in terms of transformation temperature, powder size, applied stress and heating/cooling rate. It was found that martensitic transformation temperatures of the smart composites obtained by differential scanning calorimetry (DSC) were almost equal to those of NiMnGa FSMAPs. The shape recovery of the composites was confirmed in the strain-temperature curves obtained by dynamic mechanical analysis. Clear shape change was recognized corresponding to the martensitic transformation temperatures. The shape memory properties depend on heating/cooling rate, particle size and applied stress. Lower heating/cooling rate and smaller particle size brings better shape memory properties. This is because thermal conductivity of polymer is low and the amount of defects such as pores introduced during curing decreases with decreasing particle size. The improvement of processing is needed to reduce material defects.

Abstract: The Ti50Ni25Cu25 particle/Al composite was fabricated with 30 vol.% Ti50Ni25Cu25 particles by hot pressing and followed by extruding methods. The internal friction (IF) measurements of the composite were carried out on an inverted torsion pendulum. Ti50Ni25Cu25 particles embedded in Al matrix improve the damping capacity of the composite. The internal friction behavior of Ti50Ni25Cu25 particles is consistent to that of the Ti50Ni25Cu25 bulk material. The mismatch of thermal expansion coefficients between Ti50Ni25Cu25 and Al contributes to the damping capacity of the composite. A high damping capacity of the composite could be obtained at low vibration frequency and large vibration amplitude.