Long-term Properties of a High Temperature FDM Material

Information about the mechanical properties are essential for designers in order to design products for application. Particularly for a dynamical application, like in the automotive industry or aircraft, the fatigue and creep behavior of the parts has to be known, so that the parts fulfill the calculated product life cycle. In this project, the fatigue behavior of Fused Deposition Modeling (FDM) components built with Ultem 9085 and Ultem 1010 is investigated. The dynamic properties of the material Ultem 9085 are tested at low and higher temperatures and Ultem 1010 is analyzed at higher temperatures. In further proceedings of the project, investigations on the deformation behavior of the materials at higher temperatures will follow.

Objectives
The main objective of this project is to characterize the fatigue behavior for FDM parts built with Ultem 9085 and Ultem 1010 by using the FDM standard parameters. The long and short-term properties of Ultem 9085 will be identified for different build orientations at different temperatures. For
that purpose, dynamic properties must be tested at low and higher temperatures. The aim is to detect S-N curves for the chosen FDM materials Ultem 1010 and Ultem 9085. With this information, it will be easier for designers to calculate the lifetime of a FDM part, for example an air duct, at low and high temperatures. In addition, short-term deforming tests are done at higher temperatures. Additionally, tests will be performed at a sample part which will be provided by the DMRC or by DMRC partners.

Procedure
Information about the mechanical properties are essential for designers in order to design products for application. In practice, the knowledge about the fatigue properties is crucial for a reliable component design, in addition to the static material properties. Many components are not only statically loaded because in the area of application components are also dynamically loaded. An example for this case is a fastening element of an airplane. During turbulence or take-offs and landings, the components are exposed to certain vibrations in addition to the actual static load, which leads to load peaks. Reliable statements about the relationship between the number of cycles and the load can be made with the help of S-N curves so that the risk of an unexpected component failure is significantly minimized. The proceeding of the project is divided into different work packages. The first work package includes the fatigue tests at five different temperatures for the build orientations X, Y and Z. In the first part of this project, tensile bars are produced on a Stratasys Fortus 400 mc FDM system and theyare dynamically tested to determine temperature specific fatigue curves. The tensile bars are conditioned according to ASTM 618 before they are tested. Figure 1 shows the S-N curves for different build directions X, Y, and Z for Ultem 9085.

The aim of this work package is to detect S-N curves for the chosen FDM material Ultem 1010 and Ultem 9085. With this information, it will be easier for designers to calculate the lifetime of a FDM part at low and high temperatures. Dynamic testing of plastics is associated with some peculiarities due to the plastic-specific material behavior. For metallic materials dynamic test can be performed with
a frequency of e.g. 100 Hz. However, plastics reach the softening temperature range at high test frequencies because of internal friction of the molecules with simultaneously bad heat conduction and low temperature resistance. This leads to a premature failure of the specimens in comparison with
the metallic materials. Therefore, the dynamic testing of the thermoplastic components has been performed at a significantly reduced test frequency which leads to an increase of the test duration.
In the next work package, short time deformation tests at higher temperatures will be performed to analyze the deformation behavior because fatigue tests in a range of pulsating tensile stresses lead to additional creep effects. In general, amorphous thermoplastics have a very low creep behavior, however, creep or deformation effects will increase with higher temperatures. In order to analyze the deformation behavior, short time deformation tests will be performed at the same positive temperatures which are used for fatigue tests. In addition to work package 1, the fatigue behavior of a real part will be analyzed in a further work package. Fatigue tests of a sample part should deliver the information how well or badly S-N-curves can be used for application.

Latest results
In the past project year, the fatigue behavior of Ultem 9085 at different temperatures as well as the fatigue behavior of Ultem 1010 was investigated. The results of preliminary tests show that the temperature has a significant influence on the static mechanical properties. In the following fatigue tests the temperature also has a significant influence on the fatigue behavior.