The goal of this academic project was to study the effects of different variables on the damage progression around a central hole in carbon fiber composite coupon specimens. The tracked variables included the type of layup, stress ratio, stress levels, and damage mechanisms observed in each specimen. In-situ x-ray of the individual laminates recorded the extent of damage, mostly longitudinal splitting, as a function of the cycle count. The following lay-ups were included in the experiment: [45/90/-45/02/45/02/-45/0]s, [±5/65/(±5)2/-65/±5]s, and [±5/65/(±5)2/-65/5/65]s. More specifically, the objective of this study was to determine the stress levels at which detectable damage started to develop. The researchers chose to apply 50,000 cycles at each stress level and once damage was detected, the stress level was typically raised by 34.5 MPa (5 KSI), and then cycled another 50,000 cycles until damage exceeding 1.27 cm (0.50") in length was observed. Once the damage exceeded 1.27 cm (0.50"), cycling was continued to 1,000,000 cycles. Upon completion of the fatigue cycling, each specimen's residual strength was determined. The damage length versus stress level was plotted as a way to compare damage onset stresses and growth as a function of lay-up and stress ratio.

The goal of this academic project was to study the effects of different variables on the damage initiation and progression around four bolt holes of a joint in carbon fiber/graphite epoxy composite coupons. The tracked variables included the type of layup, R values, stress levels, and damage mechanisms observed in each specimen. In-situ x-ray of the individual coupons recorded the extent of damage, mostly longitudinal splitting and bearing failure, as a function of the cycle count. The following lay-ups were included: [45/90/-45/02/45/02/-45/0]s, [04/45/03/90/0]s, [±5/65/(±5)2/-65/±5]s, and [±5/65/(±5)2/-65/5/65]s, In particular, the objective was to determine the stress levels at which detectable damage starts developing by applying 50,000 cycles at incremental stress levels. Once damage was initially detected, we typically raised the stress level 2.5 ksi and cycled another 50,000 cycles until damage reached a point where the bolt holes had elongated 10% of the original diameter of 0.25 inches. This type of testing was be continued for several different R ratios and comparisons were be made between the performances of different lay-ups at varying load levels. A finite element model was created in ABAQUS to help understand the stress fields within the laminates.

Thesis (PhDApSc)--University of South Australia, 2002.

Flush repairs to military aircraft are expected to become more prevalent as more thick skin composites are used, particularly on the surface of the fuselage, wings and other external surfaces. The use of these repairs, whilst difficult to manufacture provide an aerodynamic, ???stealthy??? finish that is also more structurally efficient than overlap repairs. This research was undertaken to improve the design methodology of scarf repairs with reduced material removal and to investigate the damage tolerance of scarf repair to low velocity impact damage. Scarf repairs involve shallow bevel angles to ensure the shear stress in the adhesive does not exceed allowable strength. This is important when repairing structures that need to withstand hot and humid conditions, when the adhesive properties degrade. Therefore, considerable amounts of parent material must be machined away prior to repair. The tips of the repair patch and the parent laminate are very sharp, thus a scarf repair is susceptible to accidental damage. The original contributions include: ??? Developed analytic means of predicting the stresses within optimised scarf joints with dissimilar materials. New equations were developed and solved using numerical algorithms. ??? Verified using finite element modelling that a scarfed insert with dissimilar modulus subjected to uniaxial loading attracted the same amount of load as an insert without a scarf. As such, the simple analytic formula used to predict load attraction/diversion through a plate with an insert may be used to predict the load attraction/diversion into a scarf repair that contains a dissimilar adherend patch. ??? Developed a more efficient flush joint with a doubler insert placed near the mid line of the parent structure material. This joint configuration has a lower load eccentricity than external doubler joint. ??? Investigated the damage tolerance of scarf joints, with and without the external doubler. The results showed that scarf joints without external doublers exhibited a considerable strength reduction following low velocity impact. Based on the observations, the major damage mechanics in the scarf joint region following impact have been identified. These results demonstrated that it is important to incorporate damage tolerance in the design of scarf repairs.

Composite materials are well-renown for their strength to weight ratios and are widely used in many industries where high strength and low weight is required. Although steel is the traditional material of choice in the mining industry, and particularly for conveyor support structures, the strength and weight advantages offered by composite materials has prompted this investigation into the feasibility of using composite materials in underground mining conveyor support structures. The first phase of the project centred on establishing and applying selection criteria for the materials and processes which could be used in such a structure. Key concerns include fire performance, electrical conductivity, cost, availability and manufacturability. Based on these considerations, the project identified a phenolic-glass laminate manufactured using the RTM method (for moulded components) or the pultrusion process (for tube sections) as a possible basis for a composite conveyor support structure. The second phase of the project developed a set of design criteria for the use of composite materials in conveyor support structures and a series of preliminary designs based on current conveyor configurations. After analysing each preliminary design against key design criteria, in particular cost, weight, assembly time, susceptibility to damage and torsional loading, the Linestand Suspended - Beam configuration was selected as the preferred option. The third phase of the project used the findings of the preliminary design analysis and the key design criteria to develop a prototype final design. The prototype design is based on a hybrid style of frame. The majority of the structure is constructed from a custom pultruded beam connected with a composite connection piece, while the interface between the rollers and the frame utilises a steel bracket to reduce the risk of damage to the composite frame. The final design is 12kg lighter than the current smaller steel design of similar function. The project has demonstrated the feasibility of using composite materials in conveyor support structures and the weight savings that may be achieved.

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: P.S. Nicholson. Includes bibliographical references (leaves 135-157).

Thesis (PhD) -- University of Western Sydney, 2001. / "A thesis submitted for the degree of Doctor of Philosophy in the University of Western Sydney." Bibliography: leaves 163 - 170.

Thesis (M.S.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: Keith W. Goossen, Dept. of Electrical & Computer Engineering. Includes bibliographical references.

Thesis (M. Eng.)--Carleton University, 1999. / Includes bibliographical references (p. 164-166). Also available in electronic format on the Internet.