IIMEC Controlled Impact Testing Of Composites With And Without SMA wires and/or Carbon Nanotubes K. Sofocleous a, V. Drakonakis, H. Doumanidis a, S. L. Ogin b a University of Cyprus, Nicosia, Cyprus d University of Surrey, Guildford, UK

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INTRODUCTION Most important issue when studying impact damage is how to minimise the effect of impact damage on structural performance. The most important drawbacks of composite materials are their weak impact damage tolerance and low conductivity to electrical impulses. SMA wires have the capability of either imparting a compressive strain to a structure and reducing the damage due to impact or they can assist in dissipating impact energy through superelasticity. Carbon Nanotubes are used in a wide range of applications, but their mechanical, electronic and thermal properties of nanotubes make them ideal reinforcements of composite materials. Carbon Nanotubes have high electrical and thermal conductivity and high aspect ratio to produce conductive plastics with exceedingly low percolation thresholds

AIMS OF THE PRESENT WORK To carry out controlled impact test on composites with and without carbon nanotubes (CNTs) or Shape Memory Alloys (SMAs) wires. To compare the load history and energy absorption of composites containing CNTs or SMA wires, with composites without CNTs or SMA wires. To carry out controlled impact test and compare the load history and energy absorption on composites with CNTs and SMA wires.

MATERIALS Two-layer woven glass fabric reinforced composite laminates with epoxy resin matrix. Some laminates were reinforced with superelastic SMA wires or copper wire with a diameter of mm. The wires were incorporated in both 0 o and 90 o directions and placed between the two layers of woven cloth. Volume fraction of wires in the specimens is 2.4%. Four-layer carbon woven fabric reinforced composite laminates with epoxy resin matrix. Some laminates were reinforced with CNTs which were mixed in the resin and spread around the whole panel. Volume fraction of CNTs in the specimens is 2%. Circular specimens140 mm in diameter, were used as impact specimens (CRAG specimen geometry).

A servo-hydraulic testing machine was used for the impact testing, with the specimen clamped in a specially manufactured cage. Specimens were clamped over an annulus of 20 mm and the area exposed for impact was a panel of diameter 100 mm. A spherical glass impactor of 16 mm diameter was driven into the specimen with a constant control speed in the range 0.08 mm/sec to 200 mm/sec. Most tests have been carried out at 4 mm/sec. A video camera was used to record the sequence of damage during impact. IMPACT RIG Schematic of impact rig.

EXPERIMENTAL METHOD Two related types of impact test have been carried out. Multiple impact test: the impactor was driven into the specimen to a certain displacement at a constant speed and then returned to its initial position. Then the impactor was driven to a higher displacement and again back to initial position. Single impact test: the impactor was driven into the specimen without interruptions.

EXPERIMENTAL RESULTS – LOAD-DISPLACEMENT RESPONSE OF SINGLE IMPACT SPECIMENS WITH SMA, COPPER AND WITHOUT WIRES

Specimens without wires. The response of multiple impact test is similar to the response of single impact test. Energy absorbed during multiple impact test is about 5.4 J. Energy absorbed during single impact test is about 5.5 J. LOAD-DISPLACEMENT RESPONSE OF SINGLE AND MULTIPLE IMPACT TESTS

LOAD-DISPLACEMENT RESPONSE OF SINGLE AND MULTIPLE IMPACT TEST Specimens with copper wires have a similar response for multiple and single impact response. Energy absorbed for multiple impact test is about 6J and for single test is about 6.2 J. Specimens with SMA wires have also similar response for multiple and single impact test. Energy absorbed for multiple impact tests is about 7.3 J and single tests is about 7.4 J.

MACROSCOPIC DAMAGE DEVELOPMENT FOR SPECIMENS WITH SMA WIRES

EXPERIMENTAL RESULTS – LOAD-DISPLACEMENT RESPONSE OF SINGLE IMPACT SPECIMENS WITH AND WITHOUT CNTs.

Specimens without CNTs. The response of multiple impact test is similar to the response of single impact test. Energy absorbed during multiple impact test is about 3.31 J. Energy absorbed during single impact test is about 3.35 J. LOAD-DISPLACEMENT RESPONSE OF SINGLE AND MULTIPLE IMPACT TESTS

LOAD-DISPLACEMENT RESPONSE OF SINGLE AND MULTIPLE IMPACT TEST Specimens with CNTs have also similar response for multiple and single impact test. Energy absorbed for multiple impact tests is about 5.1 J and single tests is about 5.5 J.

COMPARISON OF ENERGY ABSORBTION FOR SPECIMENS WITH AND WITHOUT CNTs About 35% increase in energy absorption, for the specimens with SMA wires About 31% increase in energy absorption, for the specimens with CNTs. Type ofEnergyIncreased impact specimen(J) energy absorption (J) Glass specimens5.45- Glass specimens with SMA wires Carbon specimens Carbon specimens With CNTs

CONCLUSION AND FUTURE WORK Controlled impact test of glass fabric with epoxy specimens with and without SMA wires and woven carbon fibres with epoxy specimens with and without CNTs using a servo-hydraulic test rig. Specimens reinforced with SMA wires or CNTs absorb more energy than specimens without SMA wires or CNTs on impact. Further into the project SMA will be introduced into specimens with CNTs and impact tested. These specimens are expected to show even higher increase in the energy absorption. Also, another aim is to model the impact of carbon fibre/epoxy specimens with and without SMA and/or CNTs using finite element. Collaboration needed.

Acknowledgment This work was co-funded by the European Regional Development Fund and the Republic of Cyprus through the Cyprus Research Promotion Foundation (Project ΔΙΔΑΚΤΩΡ/0609/33)

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