Geometrically nonlinear analysis of laminated elastic structures

This final technical report contains three parts: Part 1 deals with the 2-D shell theory and its element formulation and applications. Part 2 deals with the 3-D degenerated element. These two parts constitute the two major tasks that were completed under the grant. Another related topic that was initiated during the present investigation is the development of a nonlinear material model. This topic is briefly discussed in Part 3. To make each part self-contained, conclusions and references are included in each part. In the interest of brevity, the discussions presented are relatively brief. The details and additional topics are described in the references cited

Thermal and Mechanical Response of Inner Cone Sample of ZrB₂-SiC Ceramic under Arc-Jet Conditions

Under arc-jet test conditions, ZrB2-SiC ceramic will undergo high temperature oxidation and develop an external glassy layer (SiO2), zirconia sub-layer (ZrO2) and SiC-depleted diboride layer (ZrB2). This study relates to finite element modeling of the effects of oxidation on heat transfer and mechanical behavior of ZrB2-SiC ceramic under arc-jet test conditions. A steady-state heat transfer FE method was employed to conduct the heat transfer analysis to obtain the temperature distribution in the inner body of the cone. The surface thermal conditions available in the literature were used in the heat transfer analysis. The resulting temperature distribution in the inner body of the cone is then applied to the thermomechanical finite element analysis to calculate the thermal stress distribution. The results show that the oxide layers affect both thermal and mechanical response of the ZrB2-SiC ceramic under arc-jet high temperature test conditions. Due to the mismatch of material properties between the bulk ZrB2-SiC and its new products after oxidation, the outer oxide layers constrain the thermal deformation of the inner bulk ZrB2-SiC thereby putting it in compression and outside oxide layers in tension

Composite Structures using Asphalt Based Roofing Scrap Materials: EIERA -- Final Report

The uses of recycled materials in composites provide the potential for large cost savings and a solution to the ever-growing disposal problem. Shingles contain petroleum based binders and fillers, which used as a valuable resource in composite production. Composites offer inherent advantages over traditional materials in regard to corrosion resistance, design flexibility and extended service life. Use of scrap-roofing shingles as a core material in glass fiber reinforced composite materials offer potential low cost composite products such as sound barrier system, railroad ties and other building materials including blocks. In the present work, processes have been developed for shredding scrap roof shingles, for making shingle blocks, and for filling hollow composite tubes. Mechanical testing was performed to compare the performance of filled composite tubes to hollow tubes and oak wood beams. Filled tubes show improvement in ultimate flexural strength by preventing buckling and crushing. Tests were also conducted to evaluate the sound attenuation capability of recycled shingle walls. It was observed that the mean sound level at the backside of the wall, measured in decibels, was greatly reduced and shows potential use for recycled shingles in a sound barrier system. University of Missouri-Rolla has collaborated with Future Tek Inc. and Lemay Center for Composites Technology for successful completion of this project. The economic benefits are truly immense. This project will impact the community by diverting thousands of tons of shingles into usable products with a real economic impact

Behavior of EB FRP Masonry Bond under Service Temperature

The interest in advanced composites in repairing and strengthening infrastructure systems has considerably increased, especially as the application externally bonded (EB) fiber reinforced polymer (FRP) has become more well established. Previous research on bond behavior has focused on impact of durability by considering exposure to harsh environmental conditions and testing the specimens after exposure, rather than testing bond performance during exposure. The influence of directly applying temperature on bond behavior represents an open topic that needs to be investigated in more detail. This study is one of the first studies to investigate the bond behavior when the composite is subjected to tension force simultaneously with applying temperature. The temperatures considered in this study were at freezing, ambient, and high temperature, which are more representative of structural elements under field conditions. A total of 16 specimens were strengthened and tested under single-lap direct shear. The key parameters investigated include (a) the type of fiber [laminate carbon vs. wet layup glass] (b) the level of temperature applied on specimen, including ambient condition 21°C (70 °F), freeze condition -18 °C (0 °F) and hot weather 49 °C (120 °F), and (c) the exposure regime (direct exposure during loading process vs. loading after exposure). Most of the specimens were subjected to tension force simultaneously with applying temperature, and the other specimens were later tested after exposure to the heating and cooling cycles. These cycles are proposed to simulate 20 years of the typical in-situ weather conditions in the Central United States. The results showed that overall the EB strengthening systems exhibited good performance when subjected to cycles of heating and cooling prior to testing. High reduction of FRP-epoxy bond properties was up to 59% when exposed to high service temperatures. Different modes of failure were observed such as debonding at fiber-matrix interface and debonding due to shearing in laminate

Design and Technologies for a Smart Composite Bridge

An all-composite, smart bridge design for shortspan applications is described. The bridge dimensions are 9.14-m (30-ft.) long and 2.74-m (9-ft.) wide. A modular construction based on assemblies of pultruded fiber-reinforced-polymer (FRP) composite tubes is used to meet American Association of State Highway and Transportation Officials (AASHTO) H20 highway load ratings. The hollow tubes are 76 mm (3 in.) square and are made of carbon/vinyl-ester and glass/vinyl-ester. An extensive experimental study was carried out to obtain and compare properties (stiffness, strength, and failure modes) for a quarter portion of the full-sized bridge. The bridge response was measured for design loading, two-million-cycle fatigue loading, and ultimate load capacity. In addition to meeting H20 load criteria, the test article showed almost no reduction in stiffness or strength under fatigue loading and excellent linear elastic behavior up to failure. Fiber optic strain sensors were evaluated on the test article during testing. Sensor characteristics are determined as preparation for permanent field installation

System Modeling and Control of Smart Structures

This paper presents multidisciplinary research and curriculum efforts at the University of Missouri-Rolla in the smart structures area. The primary objective of our project is to integrate research results with curriculum development for the benefit of students in electrical, and mechanical and aerospace engineering and engineering mechanics. The approach to the accomplishment of curriculum objectives is the development of a two-course sequence in the smart structures area with an integrated laboratory. The research portion of the project addresses structural identification and robust control methods for smart structures. A brief summary of the research results and a description of curriculum development in the smart structures area are described in this pape

Detection and Classification of Impact-Induced Damage in Composite Plates using Neural Networks

Artificial neutral networks (ANN) can be used as an online health monitoring systems (involving damage assessment, fatigue monitoring and delamination detection) for composite structures owing to their inherent fast computing speeds, parallel processing and ability to learn and adapt to the experimental data. The amount of impact-induced strain on a composite structure can be found using strain sensors attached to composite structures. Prior work has shown that strain-based ANN can characterize impact energy on composite plates and that strain signatures can be associated with damage types and severity. This paper reports the extension of this approach for damage classification using finite element analysis to simulate impact-induced strain profiles resulting from impact on composite plates. An ANN employing the backpropagation algorithm was developed to detect and classify this damag