RESUMO
Producing lightweight structures can be effectively achieved using adhesive bonding that incorporates a high-performance adhesive, eliminating the mechanical joints (rivet, bolts). Here, the proof-of-concept of tailoring the high-performance adhesive using microstructures exhibiting a negative Poisson's ratio (auxetic) is investigated using two single lap joint (SLJ) models developed in ABAQUS/Standard. The SLJ models consist of two rigid adherends that are bonded using either homogeneous or heterogeneous adhesive that produces auxetic response. In homogeneous adhesive, a negative value of Poisson's ratio is defined in the adhesive part of the models. In heterogeneous adhesive, the negative Poisson's ratio is obtained by explicitly building orthogonally-arranged elliptical voids in the adhesive part of the models. In addition, the adherend-adhesive interface is represented by cohesive elements with bi-linear traction-separation rule. The effects of using two different adhesive models and thickness on peel and shear stresses, as well as failure mechanism and joint strength, are evaluated. We found that the effect of auxetic adhesive on SLJ response is more profound in the model using heterogeneous adhesive rather than the homogeneous one, where the joint strength enhancement could achieve 45 % in reference to the baseline model. The heterogeneous adhesive embedded between adherends is able to activate ligaments, the mechanism that could not be obtained using merely homogeneous adhesive. Our proposed modeling strategy can be a starting point to further the modeling approach of bonded joints utilizing auxetic adhesive.
RESUMO
Heat stress is being exacerbated by global warming, jeopardizing human and social sustainability. As a result, reliable and energy-efficient cooling methods are highly sought-after. Here, we report a polyacrylate film fabricated by self-moisture-absorbing hygroscopic hydrogel for efficient hybrid passive cooling. Using one of the lowest-cost industrial materials (e.g., sodium polyacrylate), we demonstrate radiative cooling by reducing solar heating with high solar reflectance (0.93) while maximizing thermal emission with high mid-infrared emittance (0.99). Importantly, the manufacturing process utilizes only atmospheric moisture and requires no additional chemicals or energy consumption, making it a completely green process. Under sunlight illumination of 800 W m-2, the surface temperature of the film was reduced by 5 °C under a partly cloudy sky observed at Buffalo, NY. Combined with its hygroscopic feature, this film can simultaneously introduce evaporative cooling that is independent of access to the clear sky. The hybrid passive cooling approach is projected to decrease global carbon emissions by 118.4 billion kg/year compared to current air-conditioning facilities powered by electricity. Given its low-cost raw materials and excellent molding feature, the film can be manufactured through simple and cost-effective roll-to-roll processes, making it suitable for future building construction and personal thermal management needs.
RESUMO
Soft actuators producing large motion in a short time are mostly based on stretchable polymers actuated by pneumatic pressure; they consist of bulky components, including a motor, pump/compressor, tubes, and valves. In this study, we develop a fast-responding large-amplitude soft actuator, based on a liquid-gas phase transition, which produces a compact system. The required pressure is generated solely by the electrically induced phase transition of a fluid in a cavity, mimicking the thigmonastic movements found in plants. We discuss the critical design variables to improve the performance and propose a new design for the electrodes, which are the most critical components. Our bending actuator produces large motion in <7 s, using a low-voltage source (<50 V) that allows a much faster response than the soft actuators based on phase transition currently available.
