Browsing by Subject "roughness"

Now showing 1 - 4 of 4

An Automated Method for Geometrical Surface Characterization for Fatigue Analysis of Additive Manufactured Parts
(University of Texas at Austin, 2019) Rasoolian, Behnam; Pegues, Jonathan; Shamsaei, Nima; Silva, Daniel
Recent interest to implement additive manufactured parts into structural applications has created a critical need to better understand the fatigue behavior of these parts. Alloys such as Ti-6Al-4V are popular in the aerospace and biomedical industries due to their superior strength to weight ratio and biocompatibility. Previous works have associated fatigue behavior with surface roughness, especially radius of curvature of notches. It is therefore important to develop a fast, reliable and consistent methodology for extracting such curvatures. The contribution of this paper is in providing an automated method for extracting radius of curvature using image processing techniques and optimization. Results on fatigue life prediction indicates similar results between the automated method and manually extracted radii in a significantly shorter period of time.
Challenges during laser Powder Bed Fusion of a Near-Alpha Titanium Alloy - Ti-6242Si
(University of Texas at Austin, 2021) Patel, Sagar; Keshavarz, Mohsen; Vlasea, Mihaela
Ti-6Al-2Sn-4Zr-2Mo-Si (Ti-6242Si) is a near-α phase titanium alloy that has a greater strength up to 565 °C compared to the workhorse Ti-6Al-4V alloy with a typical service temperature of up to 400 °C. While there is a wealth of literature to help understand the laser powder bed fusion (LPBF) of Ti-6Al-4V, only a few research articles about LPBF of Ti-6242Si are available in the open literature. In this work, LPBF processing diagrams and temperature prediction models were used to investigate the impact of process parameters such as laser power, scan speed, and beam spot radius on macroscale characteristics of the builds such as density and surface roughness. The use of processing diagrams allowed for exploration of density ranges between 99.55-99.98 %, and surface roughness, Sa, ranges between 8-16 μm in Ti-6242Si processed by LPBF. Cracking in Ti-6242Si manufactured by LPBF is reported for the first time. Cracking during LPBF of Ti-6242Si was observed to strongly depend upon the predicted melting mode (conduction, transition, and keyhole) for a given set of LPBF process parameters.
Debris-Covered Glacier Energy Balance Model for Imja-Lhotse Shar Glacier in the Everest Region of Nepal
(2015-12) Rounce, D. R.; Quincey, D. J.; McKinney, D. C.; Rounce, D. R.; McKinney, D. C.
Debris thickness plays an important role in regulating ablation rates on debris-covered glaciers as well as controlling the likely size and location of supraglacial lakes. Despite its importance, lack of knowledge about debris properties and associated energy fluxes prevents the robust inclusion of the effects of a debris layer into most glacier surface energy balance models. This study combines fieldwork with a debris-covered glacier energy balance model to estimate debris temperatures and ablation rates on Imja-Lhotse Shar Glacier located in the Everest region of Nepal. The debris properties that significantly influence the energy balance model are the thermal conductivity, albedo, and surface roughness. Fieldwork was conducted to measure thermal conductivity and a method was developed using Structure from Motion to estimate surface roughness. Debris temperatures measured during the 2014 melt season were used to calibrate and validate a debris-covered glacier energy balance model by optimizing the albedo, thermal conductivity, and surface roughness at 10 debris-covered sites. Furthermore, three methods for estimating the latent heat flux were investigated. Model calibration and validation found the three methods had similar performance; however, comparison of modeled and measured ablation rates revealed that assuming the latent heat flux is zero may overestimate ablation. Results also suggest that where debris moisture is unknown, measurements of the relative humidity or precipitation may be used to estimate wet debris periods, i.e., when the latent heat flux is non-zero. The effect of temporal resolution on the model was also assessed and results showed that both 6 h data and daily average data slightly underestimate debris temperatures and ablation rates; thus these should only be used to estimate rough ablation rates when no other data are available.
Understanding the Influence of Energy-Density of the Layer Dependent Part Properties in Laser-Sintering of PA12
(University of Texas at Austin, 2019) Wörz, A.; Wudy, K.; Drummer, D.
As the demand for individualization and complex parts is continuously growing, laser-sintering of polymers is on the edge from a pure prototyping technology to manufacturing parts for applications in series production. The influences on resulting parts and layer depending part properties are well known in the literature but the understanding of the interaction between process parameters and layer dependent properties is missing and limiting the dimensioning. Within this study, tensile bars with different amounts of layers and energy densities were produced and investigated for the resulting mechanical properties, roughness, density and the degree of particle melt. The results showed a strong interaction between the energy density and amount of layers, which results in differences in the fracture behavior as well as the mechanical properties. Therefore, the presented results enable the prediction of necessary part thickness for dimensioning thin parts with laser-sintering.