For crashworthiness applications, hollow composite tubes have been proposed and studied as impact-bearing members in earlier studies to replace metal tubes and beams which resisted impact by bending. This study focusses on the effect of the addition of hollow glass microballoons (GMB) in composite tubes for compressive loading. Epoxy containing 0 to 0.3 volume fraction of GMB is used with woven glass fabrics to fabricate the specimens. The mean load and energy absorbed while progressively crushing the tubes are experimentally obtained. The variation of these properties with the addition of GMB is analyzed. It is found that the compression properties improve with the addition of hollow glass particles. To explain the different modes of energy dissipation, the basic mechanical properties of the GMB-filled composites are obtained by various mechanical tests. These results are also used in an energy-based model to predict the properties of the tubes under compression. © 2019

R. Velmurugan

Department of Aerospace Engineering

Daniel Paul

Bending (forming)

Crashworthiness

Crushing

Energy dissipation

Foams

Glass

COMPRESSION PROPERTIES

Compressive loading

ENERGY-BASED MODELS

HOLLOW GLASS MICROBALLOONS

MEAN CRUSH LOAD

PETAL FORMATION

PROGRESSIVE COMPRESSION

SYNTACTIC FOAMS

Tubes (components)

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Thin-Walled Structures

This paper examines the effect of mode I interlaminar fracture toughness (GIc) on the specific energy absorption of stitched glass/polyester composite cylindrical shells under axial compression. The laminated composite cylindrical shells used as energy absorbers, absorb large amount of impact energy during collision. Since mode I delamination in the thin wall of axially collapsed shell is one of the major energy absorbing modes, contribution of GIc to specific energy absorption (SEA) of tubes is significant during collision. The GIc values are determined through double cantilever beam (DCB) test with stitched and unstitched planar specimens. The four and six-layered cylindrical tubes of D/t ratios 29.27 and 20, respectively, with GIc values ranging from 1.68 to 8.09 kJ/m2 are prepared by stitching and are subjected to quasi-static axial compression. Increasing GIc up to certain value leads to controlled progressive crushing, which is a good energy absorbing mechanism, beyond which failure is uncontrolled. Cylindrical tubes having GIc up to 6.34 kJ/m2 leads to 40% increase in SEA for four-layered tubes and 6.6% for six-layered tubes comparing with the corresponding unstitched tubes. When the tubes have GIc of 8.09 kJ/m2, four-layered tubes undergo unstable failure, but six-layered tubes undergo stable progressive crushing with 22% increase in SEA. Transition from stable to unstable failure depends upon the thickness of tubes. An analytical model is developed based on energy approach to predetermine the steady state mean crush load of cylindrical composite shells under axial compression. The model results are validated by experimental results, and show good agreement. © 2006 Elsevier Ltd. All rights reserved.

Composites Science and Technology

Progressive crushing of stitched glass/polyester composite cylindrical shells

This paper examines the effect of plain stitching by untwisted fibre rovings in the in-plane mechanical properties and Mode I interlaminar fracture toughness of glass/polyester composites. The traditional FRP laminated composites with two dimensional fibre architecture have poor interlaminar fracture resistance and suffer extensive damage by delamination cracking when subjected to out of plane loading. Through-the-thickness reinforcement is done by stitching with twisted fibre yarns in sewing machine to increase the delamination strength, but, it degrades the in-plane mechanical properties. In this work glass woven roving mats (WRM) are stitched in the thickness direction with untwisted kevlar, glass and carbon fibre rovings of various Tex by the plain stitch. It is observed that in plain stitch, no thread cross is formed and thus no resin rich pockets are seen. Uniform distribution of fibres in the stitch roving, absence of resin rich region and lesser amount of fibre damage result in increased in-plane tensile, lap shear, flexural, transverse shear and impact strengths. Effect of stitching on Mode I delamination toughness (GIc) of glass/polyester laminates has been investigated by performing double cantilever beam (DCB) test. It is observed that stitching increases the Mode I delamination toughness up to 20 times higher than that of unstitched specimen. © 2006 Elsevier Ltd. All rights reserved.

Improvements in Mode I interlaminar fracture toughness and in-plane mechanical properties of stitched glass/polyester composites

FRP composites have usually poor through-thickness mechanical properties and, therefore, are able to sustain more loads in tension than in compression and fail as a consequence of buckling. The through-thickness reinforcement is carried out by stitching to improve the delamination strength and to reduce the in-plane crack growth rate. Experiments were performed on both stitched and unstitched laminated plates which were prepared by using woven roving glass fibre mat and chopped strand glass fibre mat with polyester resin, and the effect of stitching was studied. It is observed that stitching increases delamination strength to a great extent. There are losses in the in-plane mechanical properties due to in-plane fibre damage and creation of resin-rich pockets. Various energy-absorbing modes observed during progressive crushing of both stitched and unstitched FRP cylindrical shells under axial compression were studied both experimentally and theoretically. Analytical expressions for the calculation of energy absorption in various modes and average crush stress were derived, and the results thus obtained were compared with the experiments. © 2004 Elsevier Ltd. All rights reserved.

International Journal of Impact Engineering

The effect of stitching on FRP cylindrical shells under axial compression

Theoretical study of absorbed energy by empty and foam-filled composite tubes under lateral compression

Axial splitting of composite columns with different cross sections

Improvements in the crushing behaviour of glass fibre-epoxy composite tubes by the addition of hollow glass particles

Journal	Data powered by TypesetThin-Walled Structures
Publisher	Data powered by TypesetElsevier Ltd
ISSN	02638231
Open Access	No