Crack Propagation in 3-D Printed PLA: Finite Element Modeling, Test Bed Design, and Preliminary Experimental Results

The present study was a preliminary exploration of crack propagation in 3-D printed polylactic acid (PLA), a bio-mass generated recyclable polymer with excellent mechanical properties and many consumer and industrial applications. This material has not been explored in great depth in the literature, so little is known about its crack propagation behavior; the 3-D printed mesostructure of the material adds additional complexity to the problem. Simple finite element models of this mesostructure were created to demonstrate this and place the rest of the study in context. Three test articles were designed for 3-point-bend testing, each meant to test a different aspect of the crack development and growth. A desktop-sized testbed was designed and developed to test these articles. A series of six experiments were run, each of the test article designs in each of two print orientations. The six experiments were each replicated twice, for a total of 18 tests, to ensure repeatability and reliability of the collected data. The crack behavior overall seemed well captured using the developed experiment. Several potential improvements were identified and described. The validity of a linear-elastic, small-scale yielding assumption in the growth of cracks in PLA was also examined, as well as the crack velocity, crack stability, and fracture mode.Ope

The compounding of short fibre reinforced thermoplastic composites

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.It is generally accepted that the mechanical properties of short fibre reinforced thermoplastics do not correspond with the high mechanical properties of fibres used to reinforce them. A study is made into the methods of compounding reinforcing fibres into thermoplastics to produce short fibre reinforced thermoplastics of enhanced properties. The initial method chosen for investigation is the twin screw extrusion compounding process. Variables such as fibre feeding arrangement and extrusion screw design are found to be factors influencing the properties of carbon and glass reinforced nylon 6,6. Use is made of computer programs to predict properties, assess compound quality and estimate fibre-matrix bond strength. Investigations indicate that the presence of reinforcing fibres with enhanced lengths does not result in the predicted property increases. The reasons for this shortfall are believed to lie in unfavourable fibre orientation in injection mouldings and the reduced strain to break of these materials. Short Kevlar reinforced thermoplastics are compounded and their mechanical properties assessed. The reasons for the poor mechanical properties for these materials are identified as a poor bond strength between fibre and matrix, the formation of points of weakness within the fibres by the compounding and moulding processes and the coiled arrangement of fibres present in injection mouldings. A method suitable for the routine assessment of fibre-matrix bond strength is used to examine combinations of fibre and thermoplastic matrix. A comparison is made of the values derived from this method with values calculated from stress-strain curves of injection mouldings. This allows an understanding of the nature of the fibre-matrix bond yielded by compounding and injection moulding steps. A description is given of a novel method designed to overcome the limitations of conventional compounding routes to produce long fibre reinforced injection moulding feedstock. Further work is necessary before this method is a feasible production technique

RECYCLING PRINTERS FOR EDUCATIONAL PURPOSES

Large amounts of printers are thrown out annually, since it is usually more attractive to buy a new printer than to replace ink cartridges, especially if the apparent cost is very similar. Most of the discarded printers either end up in land fills, or are melted for recovery of the metal components. At the University of Évora, a new approach has been developed since 2007: old printers are dismantled and the parts are used in electronics and automation classes, saving the environment and helping to reduce the annual cost of running the laboratory classes. One of the most widely available and useful printers is the HP 600 series that were manufactured between 1994 and 2000. These printers, once dismantled can provide various precious components for electronic classes. These components include: 2 step motors, one 12V motor complete with gear-head and trolley, a LM35DZ precision thermometer, one contact relay, one infra-red switch, two LDRs and one high quality cable and a LPT connector that can be used in automation developments using the PC´s LPT port. The four years of experience have shown that the students are more than willing to take the time to dismantle the equipment and carefully extract the components. With the proper tools, two students can dismantle a printer and remove the parts in less than 15 minutes. This paper presents the individual components that can be removed and presents sample circuits and uses for the parts in electronic and automation laboratory classes

Printed Circuit Board (PCB) design process and fabrication

This module describes main characteristics of Printed Circuit Boards (PCBs). A brief history of PCBs is introduced in the first chapter. Then, the design processes and the fabrication of PCBs are addressed and finally a study case is presented in the last chapter of the module.Peer ReviewedPostprint (published version

Thermoplastic coating of carbon fibers

Using a continuous powder coating process, more than 1500 meters of T 300/LaRC-TPI prepreg were produced. Two different types of heating sections in the coating line, namely electrical resistance and convection heating, were utilized. These prepregs were used to fabricate unidirectional composites. During composite fabrication the cure time of the consolidation was varied, and composites samples were produced with and without vacuum. Under these specimens, the effects of the different heating sections and of the variation of the consolidation parameters on mechanical properties and void content were investigated. The void fractions of the various composites were determined from density measurements, and the mechanical properties were measured by tensile testing, short beam shear testing and dynamic mechanical analysis

Research and Technology

Langley Research Center is engaged in the basic an applied research necessary for the advancement of aeronautics and space flight, generating advanced concepts for the accomplishment of related national goals, and provding research advice, technological support, and assistance to other NASA installations, other government agencies, and industry. Highlights of major accomplishments and applications are presented

The development and evaluation of an alternative powder prepregging technique for use with LaRC-TPI/graphite composites

An alternative powder prepregging method for use with LaRC-TPI (a thermoplastic polyimide)/graphite composites is investigated. The alternative method incorporates the idea of moistening the fiber prior to powder coating. Details of the processing parameters are given and discussed. The material was subsequently laminated into small coupons which were evaluated for processing defects using electron microscopy. After the initial evaluation of the material, no major processing defects were encountered but there appeared to be an interfacial adhesion problem. As a result, prepregging efforts were extended to include an additional fiber system, XAS, and a semicrystalline form of the matrix. The semicrystalline form of the matrix was the result of a complex heat treating cycle. Using scanning electron microscopy (SEM), the fiber/matrix adhesion was evaluated in these systems relative to the amorphous/XAS coupons. Based on these results, amorphous and semicrystalline/AS-4 and XAS materials were prepregged and laminated for transverse tensile testing. The results of these tests are presented, and in an effort to obtain more information on the effect of the matrix, remaining semicrystalline transverse tensile coupons were transformed back to the amorphous state and tested. The mechanical properties of the transformed coupons returned to the values observed for the original amorphous coupons, and the interfacial adhesion, as observed by SEM, was better than in any previous sample

Automobile Recycling Policy: Findings and Recommendations

Findings and recommendations presented to the Automobitive Board of Governors, World Economic Forum, Davos.This report focuses on recycling. As an objective neutral party, MIT has compiled a knowledge base that examines the many complex issues relating to re-cycling. Although this report was prepared at the request of the Automotive board of Governors, it was not prepared solely as an industry response document. Rather, it attempts to focus on the concerted actions that both industry and government should take. MIT hopes that the document can serve as the basis for forging international consensus on a rational approach to recycling policy. This document presents the findings and recommendations of this group to the Board of Governors. In addition to these recommendations, supporting materials in the form of four appendices, tracing specific aspects of the problem of vehicle recycling and the ways in which these problems can be analyzed, are appended.International Motor Vehicle Program, Materials Systems Laborator