Control of delamination via crack growth plane design
Topic(s) : Special Sessions
Co-authors :
Ping HU (DENMARK), Marcelo A. DIAS , Michal K. BUDZIK (DENMARK)Abstract :
Understanding the behavior and failure mechanisms of composites under load is crucial. Unlike homogeneous isotropic materials, failure in composites tends to be more complex. Among various degradation modes, delamination significantly influences the service life of co-cured composite and adhesive-bonded structures, primarily due to weak interlaminar properties. Delamination typically results in reduced stiffness and strength of the structure. However, such critical issues could be mitigated during the design phase by altering geometrical or material properties [1,2].
This study investigates an effective strategy to bolster interlaminar resistance by altering interface geometry to control crack propagation. We focus on developing analytical formulas to understand and control the growth of planar cracks at width-varying interfaces in laminated materials. Two analytical models—an approximate and a semi-analytical—are introduced, considering parameters like the effective rate of interface geometry change and shape factor of the crack growth plane.
The semi-analytical and approximate analytical models were both assessed against numerical studies employing a cohesive zone model and experimental data from carbon fiber laminates. The comparisons revealed a good agreement between the analytical models and the numerical, as well as experimental outcomes. However, the approximate analytical model displays limitations when dealing with large values of the effective width rate, necessitating the use of the semi-analytical model in such scenarios due to its superior handling of significant width variations. Although the approximate model offers substantial insights into load response behaviors, the semi-analytical model proves to be more intricate in interpreting load responses. Our observations indicate that an initial width approaching zero at the loading point is beneficial in preventing a reduction in force for a given displacement. In contrast, a larger initial width results in a higher peak load, but the force diminishes as displacement increases. Furthermore, increasing both the rate of the width change and a shape factor different from unity can enhance the force along with increasing displacement during crack propagation.
Generally, the force-displacement curve is controlled by two asymptotic lines defined by the shape factor and effective width rate of the width-varying samples. This work enhances understanding of fracture phenomena in composite materials and offers insights for designing composites with unique shapes and improved crack resistance. It also addresses practical issues in composite repairs, potentially enhancing the performance and longevity of composite structures.
This study investigates an effective strategy to bolster interlaminar resistance by altering interface geometry to control crack propagation. We focus on developing analytical formulas to understand and control the growth of planar cracks at width-varying interfaces in laminated materials. Two analytical models—an approximate and a semi-analytical—are introduced, considering parameters like the effective rate of interface geometry change and shape factor of the crack growth plane.
The semi-analytical and approximate analytical models were both assessed against numerical studies employing a cohesive zone model and experimental data from carbon fiber laminates. The comparisons revealed a good agreement between the analytical models and the numerical, as well as experimental outcomes. However, the approximate analytical model displays limitations when dealing with large values of the effective width rate, necessitating the use of the semi-analytical model in such scenarios due to its superior handling of significant width variations. Although the approximate model offers substantial insights into load response behaviors, the semi-analytical model proves to be more intricate in interpreting load responses. Our observations indicate that an initial width approaching zero at the loading point is beneficial in preventing a reduction in force for a given displacement. In contrast, a larger initial width results in a higher peak load, but the force diminishes as displacement increases. Furthermore, increasing both the rate of the width change and a shape factor different from unity can enhance the force along with increasing displacement during crack propagation.
Generally, the force-displacement curve is controlled by two asymptotic lines defined by the shape factor and effective width rate of the width-varying samples. This work enhances understanding of fracture phenomena in composite materials and offers insights for designing composites with unique shapes and improved crack resistance. It also addresses practical issues in composite repairs, potentially enhancing the performance and longevity of composite structures.