Numerical assessment of the effect of composite stacking sequence on low-velocity impact damage and residual static strength in metal-to-composite adhesively bonded joints

This study is primarily based on a numerical modeling framework, supported by experimental validation, to investigate the sensitivity of damage distribution and residual strength in metal – to – composite adhesively bonded joints to both the composite material system and laminate stacking sequence following low-velocity impact. To this end, three main specimen groups were considered. In the first group, the bonded joint consisted of a metal adherend and a glass fiber – reinforced polymer (GFRP) laminate with different stacking sequences, including unidirectional [0]8, [90]8, [0/45/−45/0]s, and [45/0/−45/90]s configurations. In the second group, the composite adherend was a unidirectional carbon fiber – reinforced polymer (CFRP) laminate, while in the third group a hybrid carbon/glass laminated composite with a unidirectional stacking sequence of [C/G/C/G]s was employed. The experimental validation was conducted using the baseline configuration corresponding to the unidirectional GFRP (Uni-G) specimen group. The numerical framework adopted in this study integrates a three-dimensional Hashin damage model for the composite adherends with a cohesive zone model (CZM) for the adhesive layer, enabling accurate simulation of impact-induced damage evolution within the composite plies and the adhesive layer, as well as the subsequent lap-shear loading response. For specimens subjected to an impact energy of 2.5 J, the results indicate that GFRP laminates with stacking sequences of [90]8, [45/0/−45/90]s, and [0/45/−45/0]s exhibited 57.5%, 25.4%, and 26.5% reductions in post-impact residual strength, respectively, compared to the [0]8 laminate. Moreover, under the same impact conditions, the use of a unidirectional CFRP substrate and the hybrid carbon/glass laminate composite led to 31.5% and 30.5% improvements in post-impact strength compared to the unidirectional GFRP substrate, respectively. Damage analysis results revealed that, for each impact energy level, matrix compression damage was dominant in CFRP composites and minor in multidirectional ones, while the opposite trend was observed for fiber tensile damage.