Nonlinear and Rate-Dependent Hysteretic Responses of Active Hybrid Composites

Nonlinear electro-mechanical behaviors of piezoelectric materials and viscoelastic nature of polymers result in the overall nonlinear and hysteretic responses of active polymeric composites. This study presents a hybrid-unit-cell model for obtaining the effective nonlinear and rate-dependent hysteretic electro-mechanical responses of hybrid piezocomposites. The studied hybrid piezocomposites consist of unidirectional piezoelectric fibers embedded in a polymeric matrix, which is reinforced with piezoelectric particles. The hybrid-unit-cell model is derived based on a unit-cell model of fiber-reinforced composites consisting of fiber and matrix subcells, in which the matrix subcells are comprised of a unit-cell model of particle-reinforced composites. Nonlinear electro-mechanical responses are considered for the piezoelectric constituents while a viscoelastic solid constitutive model is used for the polymer constituent. The hybrid-unit cell model is used to examine the effects of different responses of the constituents, microstructural arrangements, and loading histories on the overall nonlinear and hysteretic electro-mechanical responses of the hybrid piezocomposites, which are useful in designing active polymeric composites.

Structural performance of flexible freeform panelssubjected to wind loads

An increased number of hurricanes and tornadoes have been recorded worldwide in the last decade,while research efforts to reduce wind-related damage to structures become essential.Freeform architecture,which focuses on generating complex curved shapes including streamlined shapes,has recently gained interest.This study focuses on investigating the potential of kerf panels,which have unique flexibility depending on the cut patterns and densities,to generate complex shapes for facades and their performance under wind loads.To investigate the kerf panel's potential capacity against wind loads,static and dynamic analyses were conducted for two kerf panel types with different cut densities and pre-deformed shapes.It was observed that although solid panels result in smaller displacement amplitudes,stresses,and strains in some cases,the kerf panels allow for global and local cell deformations resulting in stress reduction in various locations with the potential to reduce damage due to overstress in structures.For the predeformed kerf panels,it was observed that both the overall stress and strain responses in kerf cut arrangements were lower than those of the flat-shaped panels.This study shows the promise of the use of kerf panels in achieving both design flexibility and performance demands when exposed to service loadings.Considering that this newly proposed architectural configuration(design paradigm)for facades could revolutionize structural engineering by pushing complex freeform shapes to a standard practice that intertwines aesthetic arguments,building performance requirements,and material design considerations has the potential for significant practical applications.