Off-axis Crashworthiness Characteristic of Woven Glass/Epoxy Composite Box Structures

Abstract

This study investigates the influence of off-axis loading on the fracture mechanism and specific energy absorption (SEA) of glass/epoxy twill/weave composite box structures. In this regard, the off-axis angles of 5°, 10°, 20°, and 30° of loading direction with respect to the composite box axis is studied experimentally under quasi-static crushing process. At the off-axis angle of 5°, the crushing process behavior is similar to that of the axial crushing and fracture mechanisms, such as bundle fracture and interlaminar crack propagation in Mode-II are observed. These are characteristic of brittle fracture crushing mode. For crushing at an off-axis angle of 10°, additional interwall crack propagation at one side of the box is also found. This increases the energy absorbing capability of glass/epoxy composite box at this angle. The sidewall crack is a mixed-mode crack. To characterize this crack, the mixed-mode interlaminar fracture toughness, G I/IIC, is measured using asymmetric double cantilever beam (ADCB) test method. For other angles, the non-symmetrical fracture mechanisms are found at four sides of the composite boxes. The arriving of sustained crushing stage is delayed by increasing the off-axis crushing angle. Owing to this fact, the energy absorbing capability is reduced by increasing the off-axis loading angle. An analytical solution is proposed to predict the mean force of axial crushing in brittle fracture crushing mode. The off-axis crushing process of composite boxes is also simulated by finite element software LS-DYNA and the results are verified with the relevant experimental results.

Laminate Tailoring of Composite Tubular Structures to Improve Crashworthiness Design at Off-Axis Loading

“…However, according to previous studies on axial crushing behaviour and oblique loading [10] [12] [14] [15], at oblique loading, the absorbers could experience an initial peak load followed by catastrophic failure which results into low energy absorption. Extensive studies have concerned with this phenomenon [17] [18] [19].…”

Controllable Crack Propagation in Off-Axis Crushing of Stitched Composite Absorbers

“…It was found that the foam filling in a thin-walled tubes increased the amount of energy absorbed compared with empty tubes. Ghasemnejad and Hadavinia [5] have extensively investigated the axial and off-axis crashworthy behavior of CFRP and GFRP composite box structures. In their work, the inclination angles of 5˚, 10˚, 20˚, and 30˚ of loading direction with respect to composite box axis were studied experimentally under quasi-static crushing process.…”

Progressive Crushing of Polymer Matrix Composite Tubular Structures: Review

“…Progressive failure mode and Figure 9. Comparison of axial and off-axis crushing process, (a) axial crushing and (b) off-axis crushing [143]. Figure 10.…”

“…In general a tougher matrix result into a higher G IC in composites, this is beneficial in crashworthiness design [138]. Cauchi Savona et al [139] Ghasemnejad et al [142] Ghasemnejad and Hadavinia [143] studied the off-axis crashworthy behaviour of woven GFRP composite box structures. They concluded that two fracture mechanisms of bundle fracture and crack propagation delamination in Mode-II for all composite boxes at various off-axis loading was observed.…”

“…Figure 10. Various crushing stages of woven glass/epoxy composite box in axial crushing (θ = 0) and off-axis loading at (θ = 5˚) [143].…”