During the fabrication of a filament-wound composite case, which includes the winding and cure stages, the tension in the fiber can change significantly. If the level of fiber tension decreases excessively during fabrication, fiber slippage and clumping can occur. The resulting resin rich areas can significantly decrease the strength of the composite case. The objectives of the present investigation were 1) to measure the change in fiber tension during the winding and cure of a composite case wound with prepreg material, and 2) to calculate the change in tension during cure using a simulation computer program. Of particular interest was the loss of fiber tension due to resin flow (RFTL). A total of twenty-four tension loss experiments were performed using Amoco’s Thornel T40 fiber and T40/1908 prepreg materials. The parameters which were varied in the experiments were spool tension, oven heating rate, and the number of composite layers. Some of the experiments were designed to isolate and measure RFTL by comparing the changes in tension of winds of dry fiber and prepreg material. This method was not successful due to a similarity in prepreg and dry fiber tension loss characteristics. Low spool tensions were found to result in more tension loss due to resin flow (RFTL). RFTL was also greater for an increased number of layers, but was not affected by oven heating rate. During winding, significant tension loss occurred, probably due to deformation of the prepreg tow at room temperature. The change in fiber tension during cure was calculated using an existing cure simulation code (FWCURE) which was modified in this work to include the contribution to fiber tension made by the thermal expansion of the mandrel during cure. The revised code is called FWEXPAND. By adjusting the permeability model in FWEXPAND, the fiber tension during the cure of a single layer wind was accurately calculated. The predicted total RFTL of two multi-layer winds agreed reasonably well with the measured RFTL, but the rate of tension loss was overpredicted. Complete RFTL and full compaction occurred during the first ramp of the cure cycle in all of the experiments. / Master of Science

Natural fibers are gaining popularity as reinforcement materials for thermoset resins over the last two decades. Natural fibers are inexpensive, abundant, renewable and environmentally friendly. Kenaf fibers are one of the natural fibers that can potentially be used for reinforcing unsaturated polyester (UPE). As a polymer matrix, UPE enjoys a 40% market share of all the thermoset composites. This widespread application is due to many favorable characteristics including low cost, ease of cure at room temperature, ease of molding, a good balance of mechanical, electrical and chemical properties. One of the barriers for the full utilization of the kenaf fiber reinforced UPE composites, however, is the poor interfacial adhesion between the natural fibers and the UPE resins. The good interfacial adhesion between kenaf fibers and UPE matrix is essential for generating the desired properties of kenaf-UPE composites for most of the end applications. Use of a coupling agent is one of the most effective ways of improving the interfacial adhesion. In this study, six novel effective coupling agents were developed and investigated for kenaf-UPE composites: DIH-HEA, MFA, NMA, AESO-DIH, AESO-MDI, and AESO-PMDI. All the coupling agents were able to improve the interfacial adhesion between kanaf and UPE resins. The coupling agents were found to significantly enhance the flexural properties and water resistance of the kenaf-UPE composites. Fourier transform infrared spectroscopy (FTIR) confirmed all the coupling agents were covalently bonded onto kenaf fibers. Scanning electron microscopy (SEM) images of the composites revealed the improved interfacial adhesion between kanaf fibers and UPE resins. / Graduation date: 2013

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 123-127). Also available via the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 183-191). Available also in a digital version from Dissertation Abstracts.

Thesis (M.S.)--University of Alabama at Birmingham, 2010. / Title from PDF t.p. (viewed July 19, 2010). Includes bibliographical references (p. 67-70).

A non-isothermal autohesion model was developed by combining a transient finite element heat transfer model with the isothermal autohesion model. Heat transfer analyses and the interfacial strength development analyses were conducted using the non-isothermal autohesion model on a polysulfone (Udel P1700) compact tension specimen, a 64-ply graphic (Thomel T300)/P1700 unidirectional composite, and a 192-ply graphite (Hercules AS4)/P1700 unidirectional composite. A 64-ply T300/P1700 unidirectional composite was processed in a matched metal mold. Temperature data were taken and compared with the calculated values. Good agreement was observed between the calculated and the measured temperature values. A healing test which aimed at studying the interplay bond development in AS4/P1700 unidirectional composites was performed. The double cantilevered beam (DCD) Mode l fracture toughness test was selected. The DCB specimens were fractured and healed in a special fixture with different combinations of temperature pressure, and time. The healed DCB specimens were refractured and the critical strain energy release rates (G_IC) were measured. The pressure was found to be a key factor in the healing process. Temperature and time dependencies of the interply bond development were also observed. The non-isothermal autohesion model predicted a higher strength achieved in a shorter time. This was due to the extra time which was needed for the fracture interface to achieve intimate contact, and the assumption of the initial intimate contact achievement of the non-isothermal autohesion model. / Master of Science

Low profile additives (LPA) are thermoplastics that are incorporated to unsaturated polyester (UP) resins in order to improve the surface finish of UP/fibreglass composites, widely used in automotive applications. The effect of using LPA on the thermo-mechanical properties of resin transfer moulded UP/fibreglass composites is investigated. The flexural and shear properties are measured by three-point bending tests. The trend of these mechanical properties is identified for 0% to 40% LPA content. All the mechanical properties like flexural strength, flexural modulus and short beam strength reduce upon addition of LPA. The specimens fail by tension in the flexural test and show a mixed shear/tension failure mode in case of short beam tests. From scanning electron microscopy, morphological change of the fractured surface is observed with an LPA-rich phase. Glass transition temperature (Tg) measured by thermal mechanical analysis (TMA) and dynamic mechanical analysis (DMA) show reproducible data and compare well with each other. Tg is improved by LPA addition due to the development of a more compatible system compared to neat resin. Differential scanning calorimetry (DSC) is also performed to detect Tg, which gives unreliable results.

No description available.

A heightened interest in intelligent material systems has occurred in recent years due to their remarkable adaptive abilities. Intelligent materials systems, which contain sensors and actuators coupled by means of active control, frequently utilize composite materials as the skeletal structure. In order for composite materials to be utilized in intelligent material systems to their utmost capability, many material properties, including the interfacial shear strength between the embedded sensor or actuator and the matrix must be thoroughly understood.. Investigations were performed in order to examine the effects of different variables on the interfacial characteristics between a nitinol fiber and a composite matrix. First, rough, clean fiber surfaces were found to provide the best adhesion to the matrix due to the mechanical interaction of the matrix with the rough surface finish. Second, it was determined that the interfacial shear strength is not dependent upon embedded fiber length. Third, a very small diameter fiber will break before pulling out of the matrix, but overall, large fibers have a greater interfacial strength. Fourth, it was found that the initial prestrain on the fiber during processing had no effect on the interfacial shear strength of the fiber to the matrix. Fifth, it was determined that fatigue does not degrade the shear strength of any of the different initial pres trains. Finally, it was found that a coating that does not adhere well to the fiber neither macroscopically degrades nor enhances interfacial strength. / Master of Science

This research project is partnership project involving industrial, university and government collaborators. The overall objective is to develop and enhance tools for use in Resin Transfer Moulding (RTM) design technology in order to re-design existing metallic parts using composite materials. / The specific objective of this work is to present preliminary research findings of the development of an optimized design of a leading edge slat (horizontal stabilizer component) from the Bell Model 407 Helicopter. The results presented here focus on the static stress analysis and the structure design aspects. The findings will serve as a basis for future design optimization as well as further developments in the use of RTM technology in re-designing metallic aeronautic components and can be considered to be "semi-optimized". / This research is based on extensive finite element analysis (FEA) of several composite material configurations, with a comparison made with the original metallic design. Different key criteria of the part design such as ply lay-up, bracket geometry, angle and configuration are tested using FEA technology with the objective of selecting the design which is minimizing stress concentrations. The influence of the modification of model-related parameters was also studied. / Preliminary comparative studies show that the slat configuration with half brackets opened towards the inside with an angle of 70 degrees (angle between the top of the airfoil and the side of the bracket) is the best option according to minimum stress concentration and structural flexibility. This choice is confirmed by other factors such as material savings and ease of processing.