# Shape Memory Alloy Reinforced Self-Healing Metal Matrix Composites
## 5 Healing Assessment of Shape Memory Alloy Reinforced Self-Healing Metal Matrix Composites
### Healing Assessment Results
Their investigation into fatigue behavior demonstrated promising outcomes in the healing of fatigue cracks, with consistent reductions in crack length observed across all conducted fatigue tests as a result of the healing cycle and the subsequent bonding of the matrix to itself. Additionally, the healing process led to a decrease in the fatigue crack growth rate. [PERSON] et al. [72] employed a combination of low melting point alloy and SMA as healing agents in the matrix to demonstrate self-healing in hybrid SHMMCs. The investigation focused on an AA2014 matrix reinforced with NiTi SMA wires and Sn60 Pb40 solder alloy. They utilized the Taguchi L8 mixed orthogonal array technique to identify the influential design factors such as the volume percent of SMA wires, specimen size, and diameter of SMA wires on the healing response. The healing duration was found to be the most influential design factor. The researchers reported a 100% recovery in crack width, 96.95% recovery in crack depth, and 73.76% recovery in flexural strength. Another study [73; 108] on the same hybrid SHMMC demonstrated a 100% recovery in crack width, 87.85% recovery in crack depth, and 75.40% recovery in flexural strength. The studies involved the utilization of a highly sensitive eddy current test at various frequencies to measure the crack depth in SHMMCs. Additionally, apart from employing the Taguchi L8 mixed orthogonal array and analysis of variance, the researchers developed a predictive Fuzzy model based on S/N ratio to identify the optimal design factors combination for effective healing in damaged SHMMCs. [PERSON] et al. [75] investigated the self-healing behavior of a metal-matrix composite prepared using the semi-solid metal processing technique known as rapid slurry formation. They analyzed the recovery rate and microstructure of the self-healing material, confirming successful integration of the reinforcement within the matrix. Random dispersion of NiTi wires and the conversion of alpha aluminum's dendritic microstructure into a globular form through RSF improved the alloy's strength and facilitated partial crack closure. The integration of A356 alloy with NiTi wires enabled shape-memory effects, allowing the material to regain its original shape upon exposure to heat. Crack closure analysis showed a positive recovery of 44.277% on the deformed surface, highlighting the potential of this approach for designing self-healing metallic materials. However, optimizing wire distribution and orientation could further enhance mechanical properties such as strength, stiffness, and toughness. The conclusion can be drawn that the utilization of SMA reinforcements holds promise in enhancing the healing capability of metal matrix composites, with certain composites exhibiting significant recovery of mechanical properties after healing. However, limitations exist, including challenges in manufacturing at higher volume fractions of SMA reinforcement and potential instability of the composite structure at higher healing temperatures. Other challenges include poor wettability between the reinforcement and matrix, oxidation, insufficient capillary pressure, and achieving healing of macroscopic damage without compromising strength or functionality. Further research is imperative to optimize the design and processing parameters of SMA-reinforced SHMMCs and to explore their potential for practical applications.