[en] Residual thermal stresses which develop during additive manufacturing processes are often a cause of unwanted component deformation and mechanical failure. We demonstrate that this impairment can in fact be exploited to enhance the design process for shell structures, where bistability is known to emerge in particular instances due to the presence of inelastic stresses. Multistable structures are produced through a single additive manufacturing operation by considering the inherent availability of thermal stresses in certain additive technologies. This concept is demonstrated through an analytical example, numerical simulations and a physical demonstrator produced via selective laser sintering of a titanium alloy. Our findings underline these hitherto untapped capabilities of additive processes and facilitate a deeper understanding of the thermal stresses developed during manufacture. (letter)

[en] This paper combines experimental and modelling studies to provide a detailed examination of the influence of porosity volume fraction and morphology on the polarisation-electric field response of ferroelectric materials. The broadening of the electric field distribution and a decrease in the electric field experienced by the ferroelectric ceramic medium due to the presence of low-permittivity pores is examined and its implications on the shape of the hysteresis loop, remnant polarisation and coercive field is discussed. The variation of coercive field with porosity level is seen to be complex and is attributed to two competing mechanisms where at high porosity levels the influence of the broadening of the electric field distribution dominates, while at low porosity levels an increase in the compliance of the matrix is more important. This new approach to understanding these materials enables the seemingly conflicting observations in the existing literature to be clarified and provides an effective approach to interpret the influence of pore fraction and morphology on the polarisation behaviour of ferroelectrics. Such information provides new insights in the interpretation of the physical properties of porous ferroelectric materials to inform future effort in the design of ferroelectric materials for piezoelectric sensor, actuator, energy harvesting, and transducer applications.

[en] Highlights: • BN evenly dispersed in ceramic matrix and enhanced heat transfer due to the vibrations of whole chain and phonon scattering. • The pyroelectric coefficient, thermal conductivity and dT/dt have been improved with rapid heat transfer. • The output power of the harvester boosted to 65.6% with 0.1 wt% BN. -- Abstract: Recently, recycling energy from wasted heat with pyroelectric materials has received significant attention. However, pyroelectric energy harvesters generally suffer from a low energy efficiency due to the low rates of heat transfer. Here, we report high-performance thermal energy harvesting using novel hybrid pyroelectric ceramics with greatly improved heat transfer and rate of temperature changes. This is achieved by evenly dispersing 0.1 wt% hexagonal boron nitride (hBN) nanosheets into a Pb[(Mn_1/3Nb_2/3)_1/2(Mn_1/3Sb_2/3)_1/2]_0.04(Zr_0.95Ti_0.05)_0.96O₃ (lead magnesium niobate-lead antimony-manganese-lead zirconate titanate: PMN-PMS-PZT) ceramic matrix. Due to the vibrations of whole chain and phonon scattering, heat transfer through the hybrid crystalline chain is more efficient than that of unfilled PMN-PMS-PZT. It is demonstrated that the harvested power was increased by up to 65.6%. This work paved an efficient and cost-effective way to largely improve the traditional pyroelectric ceramic for thermal energy harvesting.