Structural integrity is the cornerstone for safe and reliable technology development. It demands a deep understanding of how materials behave under extreme loading and harsh environments such as high temperature, humidity, high strain rates, etc. The influence of the material microscopic structure and the power of newly developed advanced experimental and computational tools in the recent past has opened new avenues to understanding structural integrity using muti-scale and multi-physics approaches.

Material failure mechanisms are different in different classes of materials under diverse loading scenarios, such as ductile failure in alloys and brittle failure in amorphous materials, fatigue, creep, and corrosion for high-temperature applications. Investigations on void growth and coalescence allow us to understand the fundamental insights into the susceptibility of materials to ductile failure under muti-axial loading. Localized necking, where the deformation in a stressed material concentrates in a specific area and leads to premature fracture, provides a certain mechanistic understanding of ductile failure. Appropriate material models are crucial for knowing the material behavior under ductile failure and the sensitivity of voids and their interactions with each other.

Fatigue, the repeated application, and removal of stress, even at low-stress levels, can eventually lead to material failure. Understanding fatigue behavior for real-world structures requires consideration of factors like the applied stress ratio and the fatigue spectrum loading, i.e., the range of stress levels as per the actual environmental loading. These parameters are vital for designing structures that can withstand cyclic loading without succumbing to fatigue cracks.

Beyond bulk material properties, the material behavior at lower length scales provides crucial perceptions of material deformation and failure mechanisms. The microstructure and the inhomogeneities at the lower scales influence how the material responds to stress, as explored by the field of damage mechanics. By delving into this intricate relationship between the structure–property relationships, engineers can design materials that are not only strong but also resistant to various damage mechanisms.

Advanced computational tools play a significant role in analyzing and predicting structural behavior. Techniques such as phase field methods allow engineers to virtually simulate the evolution of the interfaces in the material's microstructure under stress, providing valuable insights into deformation and potential failure. The coupling of smoothed finite element method (SFEM) with Continuum Damage Mechanics (CDM) is a crucial tool for analyzing and predicting structural behavior under diverse loading conditions. SFEM allows for the virtual modeling of complex structures, while CDM incorporates damage evolution models, providing a more realistic prediction of structural response under repetitive loading.

The increasing use of composite materials and adhesively bonded structures presents new challenges. While these structures offer superior properties, potential failure mechanisms are quite complex and different from conventional structural materials. For example, material interfaces such as inter- and intra-laminar adhesive interfaces are different. Cohesive zone models and interface fracture mechanics can be employed to analyze and mitigate these potential failure mechanisms. Cohesive zone models offer promising approaches but also have limitations. They are mesh-dependent and rely on the mesh to define the crack path.

In conclusion, structural integrity is a complex concept that necessitates a multifaceted approach. By considering various mechanisms of material failure, the influence of microstructure, and the power of advanced computational tools, engineers can design safe and reliable structures. This ongoing journey of unraveling the fabric of structural integrity is essential for the development of robust infrastructure, ensuring the safety and reliability of technological advancements.

This special issue focuses on Fracture, Fatigue, and Composite Damage. The contributing authors presented their recent findings on the current advances in ductile and brittle fracture, fatigue, and microstructural damage with a variety of approaches. The importance of adhesive interface failure in composites is also emphasized in a few articles. This collection of 9 invited articles is presented in Volume 247, Issue 2.