Extrusion additive manufacturing technologies may be utilized to fabricate complex geometry devices. However, the success of these additive manufactured devices depends upon their ability to withstand the static and dynamic mechanical loads experienced in service. In this study, quasi-static tensile and cyclic fatigue tests were performed on ULTEM 9085 samples fabricated by fused deposition modeling (FDM). First, tensile tests were conducted following ASTM D638 on three different build orientations with default build parameters to determine the mechanical strength of FDM ULTEM 9085 with those supplied by the vendor. Next, different build parameters (e.g. contour thickness, number of contours, contour depth, raster thickness, and raster angle) were varied to study the effects of those parameters on mechanical strength.
Fatigue properties were investigated utilizing the procedure outlined in ASTM D7791. S-N curves were generated using data collected at stress levels of 80%, 60%, 30% and 20% of the ultimate tensile stress with an R-ratio of 0.1 for the build orientation XZY. The contour thickness and raster thickness were increased to 0.030 in. to determine the effect of those two build parameters on tension-tension fatigue life. Next, the modified Goodman approach was used to estimate the fully reversed (R=-1) fatigue life. The initial data suggested that the modified Goodman approach was very conservative. Therefore, four different stress levels of 25%, 20%, 15% and 10% of ultimate tensile stress were used to characterize the fully reversed fatigue properties. Because of the extreme conservatism of the modified Goodman model for this material, a simple phenomenological model was developed to estimate the fatigue life of ULTEM 9085 subjected to fatigue at different R-ratios. / Master of Science / Additive manufacturing (AM) is a revolutionary technology that is dramatically expanding the current manufacturing capabilities. The additive process allows the designers to create virtually any geometry by constructing the parts in layers. The layer-to-layer build technique eliminates many of the limitations imposed by traditional manufacturing methods. For example, machining is a common manufacturing technique that is used to create highly complex parts by removing material from a billet. The process of removing material to create a part is called subtractive manufacturing. Subtractive manufacturing requires sufficient clearance for tool access, in addition to complicated mounting fixtures to secure the part. These constraints often force engineers to design less optimized geometries to account for the manufacturing limitations. However, additive manufacturing allows the user greater design freedoms without a significant increase in resources. This innovative construction technique will push the boundaries of cutting-edge designs by removing many restrictions associated with traditional manufacturing technologies.
Additive manufacturing is a relatively recent technology that evolved from rapid prototyping techniques that were developed in the 1960s. Rapid prototyping is used to create rapid iterations of physical models. However, additive manufacturing aims at creating functional end-use products. The layer-to-layer build process still poses many research challenges before it will be accepted as a reliable manufacturing technique. One of the current limitations with AM technologies is the availability of material properties associated with AM materials. The layer-to-layer build process and the toolpath creates different material properties that are dependent on the orientation of the applied load. Thus, further research is recommended to provide designers with a greater understanding of the mechanical characteristics of additive manufactured materials such as ULTEM 9085.
This objective of this research is to characterize the static strength and fatigue characteristics of ULTEM 9085. The first part of the thesis focused on investigating the effects of the following build parameters on the strength of the component: build orientation, contour thickness, number of contours, contour depth, raster thickness, and raster angle. The second portion of this investigation determined the effects of fluctuating loads on the fatigue life of ULTEM 9085. Overall, the results of this investigation can be used to design more effective components using extrusion additive manufacturing technologies.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/82047 |
| Date | 08 February 2018 |
| Creators | Pham, Khang Duy |
| Contributors | Mechanical Engineering, O'Brien, Walter F. Jr., Williams, Christopher B., Case, Scott W. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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