https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1048&context=usnavyresearch

Review of fracture toughness (G, K, J, CTOD, CTOA) testing and standardization

Defects in additive manufactured metals and their effect on fatigue performance: A state-of-the-art review

Influence of defects, surface roughness and HIP on the fatigue strength of Ti-6Al-4V manufactured by additive manufacturing

Additive manufacturing of industrially-relevant high-performance parts and products is today a reality, especially for metal additive manufacturing technologies. The design complexity that is now possible makes it particularly useful to improve product performance in a variety of applications. Metal additive manufacturing is especially well matured and is being used for production of end-use mission-critical parts. The next level of this development includes the use of intentionally designed porous metals - architected cellular or lattice structures. Cellular structures can be designed or tailored for specific mechanical or other performance characteristics and have numerous advantages due to their large surface area, low mass, regular repeated structure and open interconnected pore spaces. This is considered particularly useful for medical implants and for lightweight automotive and aerospace components, which are the main industry drivers at present. Architected cellular structures behave similar to open cell foams, which have found many other industrial applications to date, such as sandwich panels for impact absorption, radiators for thermal management, filters or catalyst materials, sound insulation, amongst others. The advantage of additively manufactured cellular structures is the precise control of the micro-architecture which becomes possible. The huge potential of these porous architected cellular materials manufactured by additive manufacturing is currently limited by concerns over their structural integrity. This is a valid concern, when considering the complexity of the manufacturing process, and the only recent maturation of metal additive manufacturing technologies. Many potential manufacturing errors can occur, which have so far resulted in a widely disparate set of results in the literature for these types of structures, with especially poor fatigue properties often found. These have improved over the years, matching the maturation and improvement of the metal additive manufacturing processes. As the causes of errors and effects of these on mechanical properties are now better understood, many of the underlying issues can be removed or mitigated. This makes additively manufactured cellular structures a highly valid option for disruptive new and improved industrial products. This review paper discusses the progress to date in the improvement of the fatigue performance of cellular structures manufactured by additive manufacturing, especially metal-based, providing insights and a glimpse to the future for fatigue-tolerant additively manufactured architected cellular materials.

Architected cellular materials: A review on their mechanical properties towards fatigue-tolerant design and fabrication

The effect of manufacturing defects on the fatigue life of selective laser melted Ti-6Al-4V structures

Defect analysis and fatigue design basis for Ni-based superalloy 718 manufactured by selective laser melting

Method of constraint loss correction of CTOD fracture toughness for fracture assessment of steel components

Fatigue life prediction of small notched Ti–6Al–4V specimens using critical distance☆

It is well known that high strength metallic materials with Vickers hardness HV >400 are very sensitive to small defects. This paper discusses fatigue properties of a Ni-based Superalloy 718 with HV =~470 which was manufactured by additive manufacturing (AM). The advantage of AM has been emphasized as the potential application to high strength or hard steels which are difficult to manufacture by traditional machining to complex shapes. However, the disadvantage or challenge of AM has been pointed out due to defects which are inevitably contained in the manufacturing process. Defects of the material investigated in this study were mostly gas porosity and those made by lack of fusion. The √area parameter model was confirmed the successful application. Although the statistics of extremes analysis is useful for the quality control of AM, the particular surface effect on the effective value of defect size must be carefully considered. Since the orientations of defects in AM materials are random, a defect in contact with specimen surface has higher influence and has the effective larger size termed as √ area eff than the real size, √ area , of the defect from the viewpoint of fracture mechanics. The guide for the fatigue design and development of higher quality Ni-based Superalloy 718 by AM processing based on the combination of the statistics of extremes on defects and the √area parameter model is proposed.

Yoichi Yamashita

Papers

Defect analysis and fatigue design basis for Ni-based superalloy 718 manufactured by selective laser melting

Method of constraint loss correction of CTOD fracture toughness for fracture assessment of steel components

Fatigue life prediction of small notched Ti–6Al–4V specimens using critical distance☆

Defect Analysis and Fatigue Design Basis for Ni-based Superalloy 718 manufactured by Additive Manufacturing

Small crack growth model from low to very high cycle fatigue regime for internal fatigue failure of high strength steel