Impact of quasi-isotropic raster layup on the mechanical behaviour of fused filament fabrication parts

The development of fused filament fabrication has extended the range of application of additive manufacturing in various areas of research. However, the mechanical strength of the fused filament fabrication–printed parts were considerably lower than that of parts fabricated by other conventional methods, owing to the observed anisotropic behaviour and formation of voids by weak interlayer diffusion. Intense studies on the effect of design and process parameters of the printed parts on the mechanical properties have been done, whereas studies on the effect of build orientations and raster patterns needs special concern. The main aim of this work is to fabricate parts printed using quasi-isotropic laminate arrangement of rasters, achieved by a raster layup of [45/0/−45/90]s, and to compare their mechanical properties with those of the commonly used 0°/90° (cross) and 45°/−45° (crisscross) raster oriented parts. The quasi-isotropic–oriented samples were observed with improved mechanical behaviour in tensile, compressive, flexural and impact tests compared to the commonly employed raster orientations.

Compression Behaviour of Wire + Arc Additive Manufactured Structures

Increasing demand for producing large-scale metal components via additive manufacturing requires relatively high building rate processes, such as wire + arc additive manufacturing (WAAM). For the industrial implementation of this technology, a throughout understanding of material behaviour is needed. In the present work, structures of Ti-6Al-4V, AA2319 and S355JR steel fabricated by means of WAAM were investigated and compared with respect to their mechanical and microstructural properties, in particular under compression loading. The microstructure of WAAM specimens is assessed by scanning electron microscopy, electron back-scatter diffraction, and optical microscopy. In Ti-6Al-4V, the results show that the presence of the basal and prismatic crystal planes in normal direction lead to an anisotropic behaviour under compression. Although AA2319 shows initially an isotropic plastic behaviour, the directional porosity distribution leads to an anisotropic behaviour at final stages of the compression tests before failure. In S355JR steel, isotropic mechanical behaviour is observed due to the presence of a relatively homogeneous microstructure. Microhardness is related to grain morphology variations, where higher hardness near the inter-layer grain boundaries for Ti-6Al-4V and AA2319 as well as within the refined regions in S355JR steel is observed. In summary, this study analyzes and compares the behaviour of three different materials fabricated by WAAM under compression loading, an important loading condition in mechanical post-processing techniques of WAAM structures, such as rolling. In this regard, the data can also be utilized for future modelling activities in this direction.

Modelling the Variability and the Anisotropic Behaviour of Crack Growth in SLM Ti-6Al-4V

The United States Air Force (USAF) Guidelines for the Durability and Damage Tolerance (DADT) certification of Additive Manufactured (AM) parts states that the most difficult challenge for the certification of an AM part is to establish an accurate prediction of its DADT. How to address this challenge is the focus of the present paper. To this end this paper examines the variability in crack growth in tests on additively manufactured (AM) Ti-6Al-4V specimens built using selective layer melting (SLM). One series of tests analysed involves thirty single edge notch tension specimens with five build orientations and two different post heat treatments. The other test program analysed involved ASTM standard single edge notch specimens with three different build directions. The results of this study highlight the ability of the Hartman–Schijve crack growth equation to capture the variability and the anisotropic behaviour of crack growth in SLM Ti-6Al-4V. It is thus shown that, despite the large variability in crack growth, the intrinsic crack growth equation remains unchanged and that the variability and the anisotropic nature of crack growth in this test program is captured by allowing for changes in both the fatigue threshold and the cyclic fracture toughness.

Anisotropy in ultrasonic pulse velocity and dynamic elastic constants of laminated sandstone

Some rocks of the crust, such as sandstones, contain fabric elements including lamination. In general, these rocks show anisotropic behaviour. In this study, anisotropic behaviour of ultrasonic pulse velocities (Vp and Vs) and dynamic elastic constants (elastic modulus (E) and Poisson's ratio (ν)) were investigated for a laminated sandstone. For this purpose, some cylindrical specimens of the sandstone were prepared at angles (β) of 0°, 30°, 45°, 60° and 90° to lamination direction. The Vp, Vs, E and ν were measured for the specimens for the different β values. The study confirms that anisotropy is one of the most important factors affecting V­, Vs, E and ν. The obtained results reveal that Vp, Vs and E show a decreasing trend with an increase in β from 0° to 90°; whereas ν shows an increasing trend. According to the values of maximum and minimum Vp, Vs, E and ν for different β values, anisotropy ratios for sandstone samples are 1.16, 1.26, 1.52 and 1.15, respectively. Finally, it can be concluded that calculated Vp, Vs, E and ν corresponding to different β values are useful for the analysis and design of geotechnical projects in the absence of borehole explorations.