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A textbook style development of viscoplasticity is presented. For completeness, the report also includes a detailed review of plasticity and viscoelasticity. The combination of plasticity and viscoelasticity is the basis for the so-called viscoelastic-plastic model developed herein. Other combo- viscoplastic models are also introduced. Each constitutive model is introduced with conceptual one-dimensional stress-strain models and then generalized for multidimensional stress space. Furthermore, each model is cast in an incremental form appropriate for numerical solution techniques. Finite element algorithms are outlined for incorporating these nonlinear constitutive models into boundary value problems. In particular, tangent stiffness and initial strain methods are discussed. The viscoelastic-plastic model is compared to experimental data for plexiglas and sea-ice to illustrate the versatility of the model in replicating nonlinear creep and flow of these materials. Moreover, the identification of the model parameters are shown to be no more difficult than the identification of parameters for the classical theories of plasticity and viscoelasticity.

Two subgrades and four rigid pavement test sections were constructed and instrumented to recover experimental information of soil/rigid pavement behavior beneath static loadings. Pavement deflections and pavement/soil strain data were recorded for incremental static loads applied to a 30 inch diameter steel plate. Tests were conducted for comparison of experimentally collected data with Westergaard and elastic layer analyses of the test sections to investigate whether a consistent mathematical relationship exists between the two methods of analysis. To this end material characterizations were carried out for the component materials in the 4 different pavement sections and analytically predicted and experimentally obtained response data were compared.

The report is concerned with the design of concrete overlays for flexible pavements. The conventional Westergaard analysis for the design of concrete overlays is reviewed and its weaknesses are enumerated. A review of layered theory indicated that an elastic layered solid approach to overlay design would predict an overlay thickness thinner than that suggested by Westergaard and, thus it offers a dollar savings in construction costs without a loss in rated load capacity. A field test section consisting of overlays of different thicknesses was constructed and load tested to evaluate the appropriateness of the new theoretical approach and also to verify the assumed failure criterion. A limited strain concept was selected as the failure mode; that is, the maximum tensile strain in the concrete at the overlay-pavement interface should be limited to a prescribed maximum value. (Author)

Increasing operational use od ice areas in polar regions has heightened the requirement for improved knowledge and techniques to analyze the behavior of sea ice. Previous studies on elastic behavior are reviewed with emphasis placed on plate analysis. Classical plate theory and the finite element method are compared in analyzing ice plates, with special attention given to sea-ice airfields. Since elastic analysis is not totally representative of actual ice behavior, a general formulation is presented which gives the assumptions and procedures for both viscoelastic and nonlinear domains of sea-ice behavior. A laboratory program is being initiated to determine material properties that are necessary to extend sea-ice analysis into the inelastic range. (Author)

The report describes a recent Naval Civil Engineering Laboratory study of airfield pavement overlay design that indicates that elastic layered analysis may be a better design approach than any other currently available technique. A finite element theory of analysis has been developed that considers horizontal sliding between layers, and the superimposed load effects of multiple-wheel landing gear. This theory also provides for automatic finite element mesh generation, and automatic plotting of stress, strain, and displacement output data. The report also presents a review of the literature about fatigue of plain concrete. It reveals information about beam and cylinder testing but discloses no conclusive experimental work on the fatigue behavior of uniformly supported pavement slabs. Fatigue behavior estimates based upon beam and cylinder tests would necessarily have to be conservative and therefore self-defeating insofar as achieving economy of design by adoption of minimum feasible thickness of pavement slab overlays. (Author)

A time-dependent, yield-failure criterion was developed and utilized in the analysis of a variety of viewport configurations. A RANGE OF THICKNESS/MINOR DIAMETER RATIOS FROM 50.25 TO 1.75 AND INCLUDED ANGLES FROM 60 DEGREE TO 120 DEGREE WERE ANALYZED BY THE FINITE ELEMENT TECHNIQUE. Using the viewport structural analysis in conjunction with the yield-failure criterion for acrylic, time- dependent operating depths were determined as a function of viewport configuration. An experimental investigation was performed to validate the analytical results. Six full- scale viewports were tested for a year under simulated operational conditions that included simultaneous cycling of pressure and temperature, 0 to 4,000 psi and 70 to 35 F, respectively. Comparison of analytical and experimental results indicated excellent agreement for the physical location of viewport failure at specified loading histories. Design recommendations are presented in the form of design curves which enable the design of a conical acrylic viewport for a specified operating pressure and duration under load. Design information is given also on sealing with a conventional 0-ring, as well as guidelines for elevating a viewport in its flange. (Author-PL)

The objective was to investigate the predictability and effectiveness of reinforced concrete beams made with Fast-Fix 1 cement. Fourteen simply supported beams were designed with the beam parameters systematically varied in order to observe a wide range of structural response when the beams were loaded to failure. The ultimate strength and mode of failure of test specimens were compared with predicted results based on the ultimate strength design assumptions of the ACl Code. In addition, 'elastic' behavior in terms of beam stiffness was compared to calculated stiffnesses based on the working stress design assumptions of the ACl Code. The performance of two Fast-Fix beams was also compared with the test results of 'duplicate' beams made with portland cement. (Author)

The purpose of this investigation was to obtain information required for the use of Fast-Fix 1 concrete as a structural material. In particular, the effects of concrete mix design parameters and aging were investigated to determine if varying them would permit attaining compressive strengths in excess of 2,500 psi without the use of retarding agents. In addition, splitting tensile strength and compressive stress-strain relations were determined for standard control cylinders. Recommendations are presented in the form of design curves which enable one to design a mix for a specified compressive strength and set time. (Author)

Analysis of a design of a pressure hull incorporating 12 spherical pentagons of acrylic plastic bonded together to form a sphere with an outside diameter of 66 inches and a wall thickness of 2.5 inches. Steel penetrations were located at the two poles. The experimental results were obtained from strain gage data from two independent pressure tests to 500 psi on two acrylic plastic hulls of the same design. The finite element analysis of the hull structure placed particular emphasis on the acrylic plastic-steel boundary. The boundary conditions at the acrylic plastic-steel interface were two extreme cases: fixed and free. A time-dependent yield-failure criterion for acrylic plastic was combined with the structural analysis to provide an operating depth curve as a function of both time and temperature. Comparison of the finite element and experimental results indicated excellent agreement. At a temperature of 70 F and a maximum of 50 hours load duration, the acrylic plastic hull can operate to 1,000 feet with a safety factor of 1.5 based on yield and a safety factor of 2.6 based on collapse. Design recommendations are also presented to provide guidelines for future design of the hull and its integration with an undersea vehicle. (Author, modified-PL)

The strongly polar reagents, having an increased adsorption capacity on calcite (possibly chemical bond) produce a significant improvement in grindability. The reagent effect on quartz grinding is significantly lower than on calcite, owing to the weaker interaction between the solid surface and the reagent molecules., The strongly polar reagents, having an increased adsorption capacity on calcite (possibly chemical bond) produce a significant improvement in grindability. The reagent effect on quartz grinding is significantly lower than on calcite, owing to the weaker interaction between the solid surface and the reagent molecules.