The problem of determining whether a crack impinging on an interface will penetrate into the substrate or deflect along the interface is vital to the effective design of layered and composite material systems. Of particular interest is the transition between crack propagation by penetration through an interface and deflection along an interface. There has been a great deal of work done on this problem to determine what parameters and formulations are necessary to accurately determine under what conditions penetration-deflection transition will occur. Previous work has studied this problem using stress-based, energy-based, and combined stress-energy-based approaches. Most recently, a combined stress-energy-based approach was implemented via a cohesive-zone formulation; this work showed the conceptual basis and correctness of the cohesive-zone approach, however only presented limited investigation into the behavior penetration-deflection transition. Work presented here expands this investigation on transition, exposing trends and behavior that emerge as certain dimensionless groups are varied. Principles of linear elastic fracture mechanics and, as in previous work, cohesive-theory are applied to a bi-material system in tension through the use of the commercial finite element analysis package ABAQUS. Dimensionless groups, including strength ratios, toughness ratios, fracture-length scales, and substrate toughness scales are varied systematically to show resulting system behavior in a generalized fashion. In using the cohesive-zone method, aspects of previous stress-based and energy-based formulations are reproduced. It is also shown where these formulations cease to be valid, revealing unique and previously undetected transitional interface fracture behavior. The results presented here will prove valuable in interface design as the described generalized trends can be used as references in the design of new layered and composite systems. / Graduation date: 2013

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xv, 133 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 126-133).

This thesis summarizes the results of an experimental investigation involving the testing of push-out specimens with channel shear connectors. The test program involved the testing of 78 push-out specimens and was aimed at the development of new equations for channel shear connectors embedded in solid concrete slabs and slabs with wide ribbed metal deck oriented parallel to the beam. <p>The test specimens were designed to study the effect of a number of parameters on the shear capacity of channel shear connectors. Six series of push-out specimens were tested in two phases. The primary difference between the two phases was the height of the channel connector. Other test parameters included the compressive strength of concrete, the length and the web thickness of the channel. <p>Three different types of failure mechanisms were observed. In specimens with higher strength concrete, failure was caused by the fracture of the channel near the fillet with the channel web acting like a cantilever beam. Crushing-splitting of concrete was the observed mode of failure in specimens with solid slabs when lower strength concrete was used. In most of the specimens with metal deck slabs, a concrete shear plane type of failure was observed. In the specimens involving this type of failure, the channel connector remained intact and the concrete contained within the flute in front of channel web sheared off along the interface. <p>The load carrying capacity of a channel connector increased almost linearly with the increase in channel length. On average, the increase was about 39% when the channel length was increased from 50 mm to 100 mm. There was a further increase of 24% when the channel length was increased from 100 mm to 150 mm. The influence of web thickness of channel connector was significant when the failure occurred due to channel web fracture but was minimal for a concrete crushing-splitting type of failure. <p>The specimens with solid concrete slabs carried higher load compared to those with metal deck slabs. The increase in load capacity was 33% for specimens with 150 mm long channels but only 12% for those with 50 mm long channel connectors. <p>This investigation resulted in the development of a new equation for predicting the shear strength of channel connectors embedded in solid concrete slabs. The proposed equation provides much better correlation to test results than those obtained using the current CSA equation. <p>The results of specimens with metal deck slabs were used to develop a new equation for predicting the shear capacity of channel connectors embedded in slabs with metal deck oriented parallel to the beam. The values predicted by the proposed equation were in good agreement with the observed test values.

This thesis summarizes the results of an experimental investigation involving the testing of push-out specimens with channel shear connectors. The test program involved the testing of 78 push-out specimens and was aimed at the development of new equations for channel shear connectors embedded in solid concrete slabs and slabs with wide ribbed metal deck oriented parallel to the beam. <p>The test specimens were designed to study the effect of a number of parameters on the shear capacity of channel shear connectors. Six series of push-out specimens were tested in two phases. The primary difference between the two phases was the height of the channel connector. Other test parameters included the compressive strength of concrete, the length and the web thickness of the channel. <p>Three different types of failure mechanisms were observed. In specimens with higher strength concrete, failure was caused by the fracture of the channel near the fillet with the channel web acting like a cantilever beam. Crushing-splitting of concrete was the observed mode of failure in specimens with solid slabs when lower strength concrete was used. In most of the specimens with metal deck slabs, a concrete shear plane type of failure was observed. In the specimens involving this type of failure, the channel connector remained intact and the concrete contained within the flute in front of channel web sheared off along the interface. <p>The load carrying capacity of a channel connector increased almost linearly with the increase in channel length. On average, the increase was about 39% when the channel length was increased from 50 mm to 100 mm. There was a further increase of 24% when the channel length was increased from 100 mm to 150 mm. The influence of web thickness of channel connector was significant when the failure occurred due to channel web fracture but was minimal for a concrete crushing-splitting type of failure. <p>The specimens with solid concrete slabs carried higher load compared to those with metal deck slabs. The increase in load capacity was 33% for specimens with 150 mm long channels but only 12% for those with 50 mm long channel connectors. <p>This investigation resulted in the development of a new equation for predicting the shear strength of channel connectors embedded in solid concrete slabs. The proposed equation provides much better correlation to test results than those obtained using the current CSA equation. <p>The results of specimens with metal deck slabs were used to develop a new equation for predicting the shear capacity of channel connectors embedded in slabs with metal deck oriented parallel to the beam. The values predicted by the proposed equation were in good agreement with the observed test values.

M. Tech. Mechanical Engineering / The increased use of composite materials in different industries has led to the realization of some of its benefits and disadvantages. One of the major problems, however, is the availability of biaxial test data for different composite materials. This is because structures during application face multi-axial stress states examples of such stress state scenarios include wind turbine blades and pressure vessels. This has also led to diverse range of test methods and material compositions such as combining different fibbers. The material used in this work is polymer matrix honeycomb sandwich panels. Sandwich panels are fabricated by attaching two thin stiff skins of fiber glass or carbon fiber reinforced laminates to a lightweight core. This work addresses some of the major advantages and disadvantages of this testing method. The main objective of this study is to develop a repeatable, cost effective and time efficient method for multi-axial testing of sandwich panels using existing resources.

No description available.

No description available.

Integrally heated composite tooling (IHCT) is seen as a low cost alternative to autoclave manufacturing of polymer matrix composites (PMCs). IHCTs consist of a composite tool heated by surface heaters; temperature distribution is ensured by a thermally conductive metallic layer. The main original contributions of this thesis was the development of a new method for applying copper coatings onto carbon fibre/epoxy PMCs using pulsed gas dynamic spraying, the production of larger size samples, and the characterisation of the performance of the coatings and laminates obtained. It was shown that this method has potential for producing the thermally conductive layer in an IHCT. Another contribution was the characterisation of parameters affecting temperature distribution across IHCTs through heat transfer simulations, leading to guidelines for IHCT design.

A composite skid landing gear design investigation has been conducted. Limit Drop Test as per Federal Aviation Regulations (FAR) Part 27.725 and Crash test as per MIL STD 1290A (AV) were simulated using ABAQUS to evaluate performance of multiple composite fiber-matrix systems. Load factor developed during multiple landing scenarios and energy dissipated during crash were computed. Strength and stiffness based constraints were imposed. Tsai-Wu and LaRC04 physics based failure criteria were used for limit loads. Hashin s damage initiation criteria with Davila-Camanho s energy based damage evolution law were used for crash. Initial results indicate that an all single-composite skid landing gear may not be feasible due to strength concerns in the cross member bends. Hybridization of multiple composites with elasto-plastic aluminum 7075 showed proof of strength under limit loads. Laminate tailoring for load factor optimization under limit loads was done by parameterization of a single variable fiber orientation angle for multiple laminate families. Tsai-Wu failure criterion was used to impose strength constraints. A quasi-isotropic N = 4 (pi/4) 48 ply IM7/8552 laminate was shown to be the optimal solution with a load factor under level landing condition equaling 4.17g s. LaRC04 predicts that failures will be initiated as matrix cracking under compression and fiber kinking under in-plane shear and longitudinal compression. All failures under limit loads being reported in the metal-composite hybrid joint, the joint was simulated by adhesive bonding and filament winding, separately. Simply adhesive bonding the metal and composite regions does not meet strength requirements. Filament wound bolted metal-composite joint shows proof of strength. Filament wound composite bolted to metal cross member radii is the final joining methodology. Finally, crash analysis was conducted as per requirements from MIL STD 1290A (AV). Crash at 42 ft/sec with 1 design gross weight (DGW) lift was simulated using ABAQUS. Plastic and friction energy dissipation in the reference aluminum skid landing gear were compared with plastic, friction and damage energy dissipation in the hybrid metal-composite design. Damage in composites was modeled as progressive damage with Hashin s damage initiation criteria and Davila-Camanho s energy based damage evolution law. The latter meets requirements of aircraft kinetic energy dissipation up to 20 ft/sec (67.6 kJ) as per MIL STD 1290A (AV). Weight saving possibility of up to 49% over conventional metal skid landing gear is reported. The final design recommended includes Ke49/PEEK skids, 48 ply IM7/8552 cross member tapered beams and, Al 7075 cross member bend radii bolted to the filament wound composite tapered beam. Concerns in composite skid landing gear designs, testing requirements and future opportunities are addressed.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 98-102). Also available via the Internet.