Mechanical Engineering Commons^™

Anisotropy In Impact Toughness Of Powder Bed Fused Aisi 304l Stainless Steel, Sreekar Karnati, Atoosa Khiabhani, Aaron Flood, Frank W. Liou, Joseph William Newkirk

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The current effort involved investigation into the anisotropy of AISI 304L fabricated through laser powder bed fusion. Charpy V‐notch specimens made from material fabricated at three different build orientations were tested and analyzed. A statistically significant difference among the toughness values indicates the presence of anisotropy within the additively manufactured material. While the lowest toughness was found in vertically built specimens, the horizontal specimens were found to exhibit the highest toughness. From the fracture surfaces, an atypical mode of failure was observed. Exclusive crack propagation along the interlayer track boundaries was observed. The toughness variation correlated with the ease of …

Investigation On Microstructure And Mechanical Properties Of Porous Structures Processed By Laser Powder Bed Fusion, Samarth Ramachandra

Mechanical and Aerospace Engineering Theses

Inconel 718 (i.e., IN718) is a prominent nickel-based, precipitation-hardening superalloy which exhibits exceptionally stable mechanical and corrosion resistant properties, even at temperature range of 650ºC to 700ºC, making it suitable for a wide range of applications such as aerospace, nuclear reactors, tooling, turbines, oil and gas applications. The high toughness and work hardening offered by this superalloy, however, greatly limits the choice of machinability. The presence of low levels of aluminum permits good weldability which further allows the use of laser-based additive manufacturing (AM) to efficiently fabricate IN718 parts without the limitations associated with conventional manufacturing methods. Thanks to AM …

Experimental Investigation Of Effect Of Support Structure Geometry On The Microstructure And Metallurgical Properties Of In718 Parts Fabricated By Selective Laser Melting, Sourabh Hemant Thakare

Mechanical and Aerospace Engineering Theses

Additive Manufacturing is a modern manufacturing technique that provides extreme design freedom and the ability to manufacture multiple parts with high complexities at the same time. Various fabrication techniques have been developed, and this study focuses on selective laser melting (SLM) due to its ability to provide near-perfect parts at low cost while being able to work with a wide range of materials. In SLM, the part is manufactured, layer-by-layer, by melting and solidification of powder material under controlled inert conditions. The fabrication of complex geometries is not possible without proper allocation of support structures for the part, which keeps …

Correlation And Effect Of Process Parameters On The Properties Of Inconel 718 Parts Fabricated By Selective Laser Melting Using Response Surface Method, Bharath Bhushan Ravichander

Mechanical and Aerospace Engineering Theses

Inconel 718 (i.e., IN718) is a nickel-based superalloy that exhibits outstanding tensile and impact-resistant properties, along with good high-temperature corrosion resistance. However, the machinability is poor due to the high stiffness of IN718. Therefore, additive manufacturing provides an effective solution to overcome the work hardening. Selective laser melting (SLM) is the most common powder-bed additive manufacturing technique designed to use a high power-density laser to melt and fuse the metallic powder to fabricate functional parts with high accuracy. However, the accuracy and the functional properties of the fabricated parts are greatly dependent on the process parameters. Thus, depending on the …

Design Of Versatile Feedback Control System Components For Selective Laser Sintering, Thomas Chessman

University Scholar Projects

Selective laser sintering (SLS) is an additive manufacturing technique that involves using a laser to fuse powdered material together, layer by layer, in order to create a 3-D product. Despite its numerous benefits over traditional methods of manufacturing, including higher efficiency, versatility, and the ability to process many materials, selective laser sintering suffers from its propensity to generate structural errors during operation.

Feedback control has been shown to improve fabrication quality in other laser-based additive manufacturing techniques when implemented properly. Widespread exploration of applying feedback control in SLS might lead to significant performance improvements in this form of manufacturing.

This …

Modeling, Fabrication, And Characterization Of Porous Inconel 718 Structures Using Selective Laser Melting Process, Srihari Srivathsan

Mechanical and Aerospace Engineering Theses

Bio-inspired cellular structures are of great interest these days for many applications, from engineering research to industries. Honeycomb, Body-Centered Cubic with/without Z-struts (BCC-Z/ BCC), Face Centered Cubic with/without Z-struts (FCC-Z/ FCC), and Triply Periodic Minimal Surface (TPMS) such as Gyroid, Diamond, and Schwartz lattices are the most common bio-inspired lattice structures. These structures can be tailored based on their structural organization resulting in superior materials with lightweight properties, adequate strength, and low stiffness. Thankfully, additive manufacturing (AM) has made the fabrication of these complex cellular materials realistic. However, the use of AM could lead to several defects, such as damaged …

Predictive Model For Thermal And Stress Field In Selective Laser Melting Process -- Part Ii, Lan Li, Lei Yan, Yitao Chen, Tan Pan, Xinchang Zhang, Wenyuan Cui, Aaron Flood, Frank W. Liou

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Finite Element Analysis (FEA) is used to predict the transient thermal cycle and optimize process parameters to analyze these effects on deformation and residual stresses. However, the process of predicting the thermal history in this process with the FEA method is usually time-consuming, especially for large-scale parts. In this paper, an effective predictive model of part deformation and residual stress was developed for accurately predicting deformation and residual stresses in large-scale parts. An equivalent body heat flux proposed from the single layer laser scan model was imported as the thermal load to the layer by layer model. The hatched layer …

Predictive Model For Thermal And Stress Field In Selective Laser Melting Process -- Part I, Lan Li, Lei Yan, Wenyuan Cui, Yitao Chen, Tan Pan, Xinchang Zhang, Aaron Flood, Frank W. Liou

Mechanical and Aerospace Engineering Faculty Research & Creative Works

During the part forming in laser powder bed fusion process, thermal distortion is one big problem due to the thermal stress which is caused by the high cooling rate and temperature gradient. Therefore, it is important to know the effect of process parameters on thermal and stress evolution in the melt zone. In this paper, a 3D finite element model for Selective Laser Melting (SLM) process based on sequentially coupled thermo-mechanical field analysis was developed for accurately predicting thermal history and surface features, like distortion and residual stress. Temperature dependent material properties for performed material 304L stainless steel are incorporated …

Evaluation Of Tensile Properties For Selective Laser Melted 316l Stainless Steel And The Influence Of Inherent Process Features, Paul Swartz

Master's Theses

Optimal print parameters for additively manufacturing 316L stainless steel using selective laser melting (SLM) at Cal Poly had previously been identified. In order to further support the viability of the current settings, tensile material characteristics were needed. Furthermore, reliable performance of the as-printed material had to be demonstrated. Any influence on the static performance of parts in the as-printed condition inherent to the SLM manufacturing process itself needed to be identified. Tensile testing was conducted to determine the properties of material in the as-printed condition. So as to have confidence in the experimental results, other investigations were also conducted to …

Effect Of Wall Thickness And Build Quality On The Compressive Properties Of 304l Thin-Walled Structures Fabricated By Slm, Myranda Spratt, Sudharshan Anandan, Rafid M. Hussein, Joseph William Newkirk, K. Chandrashekhara, Heath Misak, Michael Walker

Materials Science and Engineering Faculty Research & Creative Works

The specific strength of lightweight lattice structures built with SLM is of interest to the aerospace industry. Honeycombs were manufactured with increasing wall thicknesses (which increases density) and tested under compression. The optimal strength to density ratio was determined from the resulting data. The build quality was also evaluated to determine how/if the results were influenced by the specimen quality. Differences between the nominal and as-built geometry were identified, but considered to be minimal. Microstructural evaluation of the specimens revealed a possible dependence on the ‘border scan’ properties, as the thickness of the specimens was such that the board scan …

The Influence Of Build Parameters On The Compressive Properties Of Selective Laser Melted 304l Stainless Steel, Okanmisope Fashanu, Mario F. Buchely, R. Hussein, S. Anandan, Myranda Spratt, Joseph William Newkirk, K. Chandrashekhara, H. Misak, M. A. Walker

Materials Science and Engineering Faculty Research & Creative Works

Process parameters used during Selective Laser Melting (SLM) process have significant effects on the mechanical properties of the manufactured parts. In this study, the influence of two build parameters (build orientation and hatch angle) on the compressive properties of 304L stainless steel was evaluated. SLM 304L samples were manufactured using three hatch angles, 0°, 67°,105° and two orientations, z-direction and x-direction, and tested using a compression frame according to ASTM E9-09. Bulk density was measured according to ASTM C373-17 before compression. Properties evaluated were the bulk density, yield strength, strength at 15% plastic-strain and strength at 30% plastic-strain. Results showed …

Design Of Lattice Structures With Graded Density Fabricated By Additive Manufacturing, Wenjin Tao, Yong Liu, Austin T. Sutton, Krishna C. R. Kolan, Ming-Chuan Leu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Lattice structures fabricated by Additive Manufacturing (AM) processes are promising for many applications, such as lightweight structures and energy absorbers. However, predicting and controlling of their mechanical behaviors is challenging due to the complexity of modeling and the uncertainties exist in the manufacturing process. In this paper, we explore the possibilities enabled by controlling the local densities. A set of lattice structures with different density gradients are designed using an implicit isosurface equation, and they are manufactured by Selective Laser Melting (SLM) process with 304L stainless steel. Finite element analysis and compression test are used to evaluate their mechanical properties. …

Controlling Phase Fractions Of 304l-Ss In Selective Laser Melting Using Cooling Rate, Eberechukwu Anthony Okoro

Masters Theses

"This study examines the thermal profile and the ferrite-austenite phase fractions upon heating and cooling of 304- stainless steel powder via Selective Laser Melting (SLM). Experiments were performed to validate the ABAQUS finite element model, while the phase transformation simulation was performed using MatCalc and ThermoCalc. A correlation between the thermo-mechanical changes in ABAQUS and the microstructural changes from MatCalc was obtained by matching their cooling rates. The result indicates that cooling rate has a significant effect on the phase fractions of FCC and BCC formed in 304L stainless steel via the SLM process. The results also indicate that for …

Three Dimensional Finite Element Model For Residual Stresses In Parts Manufactured By Slm And Ebm, Jesus Gerardo Reyes Schuldes

Open Access Theses & Dissertations

Ongoing research efforts in industry and academia have a focus on optimal build parameters that lead to suitable mechanical properties with minimum defects in parts manufactured by powder bed fusion additive manufacturing technologies, such as Electron Beam Melting (EBM) and Selective Laser Melting (SLM). Additional and significant resources, including energy, time, and money are spent as a result of obligatory post-manufacturing heat and/or mechanical treatment to ensure optimum mechanical properties. One intrinsic fault in these technologies, which contributes to the need for treatment processes after part fabrication, is the creation of residual stresses during these processes. Residual stresses remain in …

Metals Am Design For Manufacturing, Maren Cosens, Ben Wong, Kevin Hale

Mechanical Engineering

We are looking to improve upon the current post processing techniques for metal additive manufacturing (AM). This project, sponsored by Lawrence Livermore National Laboratory (LLNL), will investigate ways to improve the design of stainless steel 316 parts made by AM, and how these designs will help with post processing techniques. We hope that the findings regarding stainless steel will apply to to improve the AM and post processing handshake in general. In particular, the project will focus on including different features in different basic part design shapes to aid in fixturing and post-processing of the part made by AM. This …

Continuum Modeling Of The Densification Of W-Ni-Fe During Selective Laser Sintering, Connor M. West

Master's Theses

The purpose of this thesis is to effectively model the time history of the temperature distribution during the selective laser sintering process and use this information to investigate the resulting relative density. The temperature is a critical parameter of the process because it directly effects the overall quality of the part. First, an efficient, affordable, and reliable simulation was developed within the finite element software, Abaqus. Next, the results from the simulations were compared to the experimental results performed by Wang et al. (2016). The FEA model consisted of a 3 layer simulation. Multiple simulations at various laser recipes were …

Radiation Heat Transfer In A Particulate Medium Using A Ray Tracing Method, Manish B. Patil

LSU Master's Theses

In the present work, a complete 3D simulation of ray tracing model is developed for studying the radiation heat transfer, associated with laser based additive manufacturing, in both thick and thin particulate beds by using the Monte Carlo method. Additional program is developed for creating different types of packing structures such as simple cubic, rhombohydral and random packing. The scattering mechanisms in the particulate beds for large opaque spheres are evaluated using the specular and diffuse reflection methods. Further, a novel approach has been added to the model to include isotropic, forward and backward scattering mechanisms for a medium which …