Cyclic electromechanical response of poly(vinylidene fluoride)
27 Jun 2019-International Journal of Materials and Structural Integrity (Inderscience Publishers)-Vol. 13, pp 160-171
TL;DR: In this article, the results of cyclic electromechanical experiments conducted on uniaxially stretched poly(vinylidene fluoride) (PVDF) films were carried out over a range of applied displacement amplitude, superposed on an initial stretch on the test samples.
Abstract: In this study, we present the results of cyclic electromechanical experiments conducted on uniaxially stretched poly(vinylidene fluoride) (PVDF) films. The experiments were carried out over a range of applied displacement amplitude ranging from 0.5 mm to 1.5 mm, superposed on an initial stretch on the test samples. The strains were calculated using non-contact speckle monitoring method. The hysteresis plots of mechanical and electromechanical cyclic responses are presented. Stress relaxation was observed up to 70% in orthogonal to stretch direction and 16% in the stretch direction. Observed piezoelectricity along both the directions is reported and discussed in the paper.
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TL;DR: In this article, the authors used two approaches to model cyclic stress with the number of cycles and the effect of cyclic loading on the material, in terms of entropy generation for mechanical and electrical response, is considered for modelling and this approach is adopted to model the PVDF response when subjected to cyclic load.
Abstract: Polyvinylidene fluoride (PVDF) is a piezopolymer, and it has numerous applications as sensors and actuators. Uniaxially stretched PVDF subjected to cyclic stresses finds usage in different applications. Characterising the cyclic response of PVDF through appropriate models is important. In this study, we used two approaches to model cyclic stress with the number of cycles. In the first approach, the evolution equations are used and adopted to model the variation of the cyclic mechanical response of PVDF to track the cyclic response at each time step. In the second approach, the effect of cyclic loading on the material, in terms of entropy generation for mechanical and electrical response, is considered for modelling and this approach is adopted to model the PVDF response when subjected to cyclic loading. The mean stress and voltage variation with the number of cycles are predicted.
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TL;DR: In this article, the dominant structural factors of the local residual stress in a silicon chip are investigated quantitatively based on the measurement of a chip using stress sensor chips, where piezoresistive strain gauges were embedded in the sensor chips.
Abstract: The local thermal deformation of the chips mounted by area-arrayed fine bumps has increased drastically because of the decrease of the flexural rigidity of the thinned chips. In this paper, the dominant structural factors of the local residual stress in a silicon chip are investigated quantitatively based on the measurement of the local residual stress in a chip using stress sensor chips. The piezoresistive strain gauges were embedded in the sensor chips. The length of each gauge was 2 µm and a unit cell consisted of four gauges with different crystallographic directions. This alignment of strain gauges enables to measure the tensor component of three-dimensional stress fields separately. Test flip chip substrates were made by silicon chip on which the area-arrayed tin/copper bumps were electroplated. The width of a bump was fixed at 200 µm and the bump pitch was varied from 400 µm to 1,000 µm. The measured amplitude of the residual stress increased from about 30 MPa to 250 MPa. It was confirmed that both the material constant of underfill and the alignment structure of fine bumps are the dominant factors of the local deformation and stress of a silicon chip mounted on area-arrayed metallic bumps.
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