Governing role of the ratio of large platelet particles to ultrafine particles on dynamic and quasistatic compressive re
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Governing role of the ratio of large platelet particles to ultrafine particles on dynamic and quasistatic compressive response and damage evolution in ice-templated alumina ceramics Mahesh Banda, Sashanka Akurati, Dipankar Ghosha) Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, Virginia 23529, USA a) Address all correspondence to this author. e-mail: [email protected] Received: 29 July 2020; accepted: 29 September 2020
This study revealed that the mass ratio of large anisometric particles (platelets) to ultrafine, equiaxed particles strongly influences dynamic and quasistatic compressive response and the process of damage evolution in icetemplated alumina materials. The improved sinterability between particles of significantly dissimilar size and morphology enabled the utilization of a high mass ratio of the particles in harnessing a markedly enhanced level of strength in highly porous ice-templated ceramics. The high volume fraction of platelets increased lamellar bridge density and resulted in dendritic morphology as opposed to lamellar morphology without platelets. All the materials showed strain rate-sensitivity, where strength increased with strain rate. Materials with highly dendritic morphology exhibited the best performance in terms of maximum strength and energy absorption capacity, and the performance improved from quasistatic to dynamic regime. Direct observation of the process of damage evolution revealed the effects of both strain rate and ratio of platelets to ultrafine particles.
Introduction The ice-templating technique enables the fabrication of directionally porous ceramics [1, 2, 3, 4, 5, 6, 7, 8]. This technique relies on the unidirectional solidification of aqueous ceramic suspensions under an applied unidirectional temperature gradient. During the solidification step, the growing ice crystals reject ceramic particles at the growth front—water interface and the rejected particles accumulate in between the growing ice crystals, whereas some particles can be entrapped within the ice crystals. From the solidified ceramic suspension, ice crystals are removed through freeze-drying (sublimation) and a directionally porous ceramic is obtained. The ceramic particles that are rejected by the ice crystals develop lamella walls, whereas the particles entrapped within the crystals form lamellar bridges between the adjacent walls [1, 2, 6, 7, 8]. All the ceramic walls and pores are oriented in the direction along which ice crystals grew during the solidification step. After the freeze-drying step, sintering is performed to impart strength to the materials.
In addition to pore directionality, another unique feature of ice-templated ceramics is that they exhibit compressive strength (along the growth direction of ice crystals) higher than that of open-cell porous ceramics [9, 10]. However, the strength advantage is diminished in highly porous ice-templated ceramics, developed from low solid loading suspensions [7, 8]. Compressive strength of ice-templated ceramics depends
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