FöRFATTARE
Carlgren, Lisa

DATUM
2001-09-11

INSTITUTION
Material- och produktionsteknik / Polymerteknik

SAMMANFATTNING
Composite Integral Armor (CIA) is a multi-layer hybrid lightweight structure developed for ground vehicles, and it includes ceramics, metals, and composites. It is widely accepted that ballistic failure involves tensile fracture of the ceramic. Inducing residual compressive stresses by confinement can delay the onset of tensile failure and provide confinement of ceramic particles after failure. The goal with the present study is to induce a compressive preload of 30 Ksi in ceramic tiles, with the purpose of improving ballistic properties of ceramic materials, by means of thermal expansion and phase transformation.

Baseline CIA targets with hexagonal alumina tiles had already been fabricated in phase one, and in this second phase, targets with confined and pre-stressed tiles will be made and tested for ballistic performance compared to the baseline armor plates. The dimensions of the ceramic tiles were studied, and the tiles were machined to the specified dimensions. For the thermal concept it was decided to make frames at room temperature and confine at cryogenic temperature. Unidirectional carbon fiber/epoxy frames were chosen as confinement material. A mandrel was designed and manufactured for producing these frames using filament winding, and a number of frames was fabricated using this technique. A first attempt to confine frames and tiles was also made. For the phase transformation concept, an important literature research was carried out. Contacts were established with different companies for the future making of shape memory alloy (SMA) confinement frames, and a confinement experiment was done with a Cryofit SMA coupling on a steel rod simulating the ceramic tile.

Tiles were measured and sent away for precision machining of sides and corners, and the result was satisfactory in about 50% of the tiles. Both the alumina ceramic and the carbon fiber/epoxy frame material proved to resist the cryogenic temperature and even the thermal shock. The mandrel proved to fill its purpose: frames were made to a good tolerance and with good reproducibility. The first attempts to test confinement by thermal means were successful but close tolerance is a problem. The SMA concept seems to be expensive and frames might have to be made with important thicknesses to achieve the desired stress levels.

Future work includes stress evaluation in confined tiles; both by thermal and phase transformation means, and a comparison of the two concepts must be made based on achieved stress levels, feasibility and economical aspects.

ISSN 1402-1617 / ISRN LTU-EX--01/251--SE / NR 2001:251