Additive Manufacturing of High Performance Semicrystalline Thermoplastics and Their Composites

This work investigates the use of two semi-crystalline high performance thermoplastics, polyphenylene sulfide (PPS) and poly (ether ketone ketone) (PEKK), as feedstock for fused filament fabrication process. Composites of PPS and PEKK are emerging as viable candidates for several components in aerospace and tooling industries and additive manufacturing of these materials can be extremely beneficial to lower manufacturing costs and lead times. However, these materials pose several challenges for extrusion and deposition due to some of their inherent properties as well as thermal and oxidative responses. To better understand the properties of such systems specific to 3D printing and determine the critical parameters that make them “printable”, various rheological and thermal properties have been studied for neat as well as short fiber reinforced PPS and PEKK systems. Attempts were also made to print these materials in a customized high temperature fused filament fabrication system.Mechanical Engineerin

Photodynamic therapy for multi-resistant cutaneous Langerhans cell histiocytosis

Langerhans cell histiocytosis is a rare group of proliferative disorders. Beside cutaneous involvement, other internal organs can be affected. The treatment of cutaneous lesions is difficult and relies on topical corticosteroids, carmustine, nitrogen mustard, and photochemotherapy. Systemic steroids and vinblastine are used for recalcitrant skin lesions. However, some cases fail to respond. An 18-month old boy presented a CD1a+, S100a+ Langerhans cell histocytosis with cutaneous and severe scalp involvement. Topical corticosteroids and nitrogen mustard failed to improve the skin lesions. Systemic corticosteroids and vinblastine improved the truncal involvement but had no effect on the scalp lesions. Methylaminolevulinate (MAL) based photodynamic therapy (PDT) resulted in a significant regression of the scalp lesions. Control histology revealed an almost complete clearance of the tumor infiltrate. Clinical follow-up after six months showed no recurrence

Characterizing Material Transition for Functionally Graded Material Using Big Area Additive Manufacturing

This study examines functionally graded materials (FGM) on a polymer based large scale additive manufacturing system. FGM utilizes a less expensive material with sub-optimal mechanical properties for the majority of the part, and uses more expensive higher performance material in selected areas. This process aims to optimize cost with weight and mechanical performance. FGM is already used a variety of industries, but is not common place in additive manufacturing, specifically large scale additive manufacturing like Cincinnati Incorporated’s Big Area Additive Manufacturing (BAAM). BAAM can use a variety of plastic injection molding and extrusion style polymer pellets, which allows it to use both commodity materials and high performance engineering polymers. This study is an initial assessment of FGM using glass fiber reinforced ABS and carbon fiber reinforced ABS, and characterizes the performance of a density gradient shape function to characterize the blending of materials.Mechanical Engineerin

Reducing Mechanical Anisotropy in Extrusion-Based Printed Parts

The mechanical performance of 3D printed components is highly dependent upon the orientation of the part relative to the build plane. Specifically for extrusion-based printing systems, the bond between successive layers (z-direction) can be 10-25% weaker than in the printed plane (x-y plane). As advanced applications call for fiber reinforced materials and larger print systems (such as the Big Area Additive Manufacturing system) extend the layer time, mechanical performance in the z-direction can decrease by 75-90%. This paper presents a patent-pending approach for improving mechanical performance in the z-direction by depositing material vertically across multiple layers during the build. The “z-pinning” process involves aligning voids across multiple (n) layers, which are then back-filled in a continuous fashion during the deposition of layer (n+1). The “z-pinning” approach has been demonstrated to be an effective approach for increasing the strength (20% increase) and toughness (200% increase) of printed parts in the z-direction.Mechanical Engineerin

Z-Pinning Approach for Reducing Mechanical Anisotropy of 3D Printed Parts

The mechanical strength of extrusion-based printed parts is often greatly reduced (25-50%) in the build direction (z-direction) compared to the in-plane strength due to poor bonding between successively deposited layers. This effect can be magnified (75-90% difference) when depositing fiber-reinforced materials or larger print areas with long layer times. Therefore, a patent-pending approach has been developed that deposits material into intentionally aligned voids in the z-direction, allowing continuous material to span multiple layers. The “z-pinning” approach can be applied to several concepts for improving the interlaminar strength of extrusion-based 3D printed parts as well as techniques for applying the technology across a broad spectrum of deposition platforms and material systems. Initial experimental results demonstrate a significant improvement (>3x) in mechanical strength and (>8x) toughness for fiber reinforced components.Mechanical Engineerin

Structural Health Monitoring of 3D Printed Structures

3D printed parts are used in industry for both tooling application and smaller parts in assembled structures. Articles made through polymer based additive manufacturing are anisotropic and may have defects throughout the part. For instance, the layer to layer interactions are weaker than the in-plane printing which can cause delamination of the layers. Identifying when and where the cracks form can be very difficult if the cracks are inside the structure This paper introduces an innovative patent-pending method to monitor polymer-based 3D printed structures for internal failures by printing a highly sensitive conductive material into the part itself. When a section of the conductive material inside the part is damaged or split, the resistance across the conductive pathway increases which will indicate that the article has been damaged. We present several small printed circuits and observations that show as a crack is introduced to the structure, the resistance measured increases which alerts users that a crack has formed/propagated.Mechanical Engineerin

Investigating Canine Cognition Using an Infant Violation of Expectation Task

Infants have demonstrated object permanence understanding during violation of expectation tasks. During these tasks, infants are shown expected (e.g., ball stops at wall) or unexpected events (e.g., ball rolling through a solid wall). Infants look longer at the unexpected event versus the expected tasks (Stahl et al., 2015). Studies have shown that dogs also looked longer at an unexpected events during object permanence tasks (Pattison et al., 2010). In the current study, dogs were presented with a violation of expectation task commonly used with infants to investigate their object permanence abilities. It was hypothesized that dogs participating in the experiment would look longer at an unexpected event than an expected one