Digital image correlation for surface deformation measurement: historical developments, recent advances and future goals

This paper examines three-dimensional metallic lattices with regular octet and rhombicuboctahedron units fabricated with geometric imperfections via Selective Laser Sintering. We use X-ray computed tomography to capture morphology, location, and distribution of process-induced defects with the aim of studying their role in the elastic response, damage initiation, and failure evolution under quasi-static compression. Testing results from in-situ compression tomography show that each lattice exhibits a distinct failure mechanism that is governed not only by cell topology but also by geometric defects induced by additive manufacturing. Extracted from X-ray tomography images, the statistical distributions of three sets of defects, namely strut waviness, strut thickness variation, and strut oversizing, are used to develop numerical models of statistically representative lattices with imperfect geometry. Elastic and failure responses are predicted within 10% agreement from the experimental data. In addition, a computational study is presented to shed light into the relationship between the amplitude of selected defects and the reduction of elastic properties compared to their nominal values. The evolution of failure mechanisms is also explained with respect to strut oversizing, a parameter that can critically cause failure mode transitions that are not visible in defect-free lattices.

Elastic and failure response of imperfect three-dimensional metallic lattices: the role of geometric defects induced by Selective Laser Melting

Current state of fabrication technologies and materials for bone tissue engineering.

Functionally graded materials (FGMs) represent a class of novel materials in which compositions/constituents and/or microstructures gradually change along single or multiple spatial directions, resulting in a gradual change in properties and functions which can be tailored for enhanced performance. FGMs can be fabricated using a variety of well-established processing methods; however, it is also known that there are inherent drawbacks to existing synthesis methods. As an emerging technology that provides a high degree of control over spatial resolution, additive manufacturing (AM) provides an intriguing pathway to circumvent the drawbacks of currently available methods. AM involves the selective deposition of individual layers of single or multiple materials, and as such it offers the potential of local control of composition and microstructure in multiple dimensions; such process conditions, in principle, can be tailored to construct complex FGMs with multi-dimensional and directional gradient structures. In this review paper, our current understanding of important issues, such as modeling, processing, microstructures and mechanical properties, as related to FGMs produced via AM, are described and discussed in an effort to assess the state of the art in this field as well as to provide insight into future research directions.

Additive manufacturing of functionally graded materials: A review

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

Additively-manufactured functionally graded Ti-6Al-4V lattice structures with high strength under static and dynamic loading: Experiments

The compression behavior of Ti–6Al–4V lattice structure with a cell shape of rhombic dodecahedron, which was fabricated by electron beam melting, was investigated at different temperatures. A series of quasi-static compression tests were performed at ambient temperature, 200 °C, 400 °C and 600 °C with a strain rate of 10 −3  s −1 . Two groups of design configurations were adopted by changing the cell size and thickness of struts with the sample size maintained unchanged. The results revealed that their properties varied with different cell sizes and temperatures. Larger cell size leaded to lower modulus and strength of the lattice. Higher temperatures resulted in lower strengths, modulus, densification strains and plateau stresses. The energy absorption of lattice at high temperature was discussed, and the experimental data were compared with aluminum foams, titanium foams and stainless steel lattice. It demonstrated that the rhombic dodecahedron Ti–6Al–4V lattice structure could be applied as load-bearing components and energy absorber at high temperature.

Mechanical behavior of open-cell rhombic dodecahedron Ti–6Al–4V lattice structure

Mechanical properties of open-cell rhombic dodecahedron titanium alloy lattice structure manufactured using electron beam melting under dynamic loading

Photosensitive ZrO2 suspensions for stereolithography

3Y-TZP strengthened ZrO2 ceramics were fabricated by using digital light processing (DLP) based additive manufacturing. The effects of 3Y-TZP concentration on the relative density, linear shrinkage, microstructure, and mechanical properties of the DLP-prepared ZrO2 ceramic were investigated in detailed. High precision ZrO2 ceramic parts with lattice structure with parts were successfully prepared by using DLP. The highest relative density and flexural strength were 96.40% and 306.53 ± 6.03 MPa, respectively, when the 3Y-TZP concentration was 7.5 vol%. The strengthening mechanism was discussed in detailed.

Weidong Song

Papers

Additively-manufactured functionally graded Ti-6Al-4V lattice structures with high strength under static and dynamic loading: Experiments

Mechanical behavior of open-cell rhombic dodecahedron Ti–6Al–4V lattice structure

Mechanical properties of open-cell rhombic dodecahedron titanium alloy lattice structure manufactured using electron beam melting under dynamic loading

Photosensitive ZrO2 suspensions for stereolithography

Digital light processing of 3Y-TZP strengthened ZrO2 ceramics