Advanced Theoretical and Computational Methods for Complex Materials and Structures

The broad use of composite materials and shell structural members with complex geometries in technologies related to various branches of engineering has gained increased attention from scientists and engineers for the development of even more refined approaches and investigation of their mechanical behavior. It is well known that composite materials are able to provide higher values of strength stiffness, and thermal properties, together with conferring reduced weight, which can affect the mechanical behavior of beams, plates, and shells, in terms of static response, vibrations, and buckling loads. At the same time, enhanced structures made of composite materials can feature internal length scales and non-local behaviors, with great sensitivity to different staking sequences, ply orientations, agglomeration of nanoparticles, volume fractions of constituents, and porosity levels, among others. In addition to fiber-reinforced composites and laminates, increased attention has been paid in literature to the study of innovative components such as functionally graded materials (FGMs), carbon nanotubes (CNTs), graphene nanoplatelets, and smart constituents. Some examples of smart applications involve large stroke smart actuators, piezoelectric sensors, shape memory alloys, magnetostrictive and electrostrictive materials, as well as auxetic components and angle-tow laminates. These constituents can be included in the lamination schemes of smart structures to control and monitor the vibrational behavior or the static deflection of several composites. The development of advanced theoretical and computational models for composite materials and structures is a subject of active research and this is explored here for different complex systems, including their static, dynamic, and buckling responses; fracture mechanics at different scales; the adhesion, cohesion, and delamination of materials and interfaces

Pneumatic Tire

For many years, tire engineers relied on the monograph, \u27Mechanics of Pneumatic Tires\u27, for detailed information about the principles of tire design and use. Published originally by the National Bureau of Standards, U.S. Department of Commerce, in 1971, and a later (1981) edition by the National Highway Traffic Safety Administration (NHTSA), U.S. Department of Transportation, it has long been out of print. No textbook or monograph of comparable range and depth has appeared since. While many chapters of the two editions contain authoritative reviews that are still relevant today, they were prepared in an era when bias ply and belted-bias tires were in widespread use in the United States and thus did not deal in a comprehensive way with more recent tire technology, notably the radial constructions now adopted nearly universally. In 2002, it was preposed that NHTSA should sponsor and publish electronically a new book on passenger tires, under editorship of the University of Akron, to meet the needs of a new generation of tire scientists, engineers, designers, and users. This text is the outcome. The chapter authors are recognized authorities in tire science and technology. They have prepared scholarly and up-to-date reviews of the various aspects of passenger car tire design, construction and use, and included test questions in many instances, so that the book can be used for self-study or as a teaching text by engineers and others entering the tire industry

Nondestructive, quantitative and local assessment of residual elastic properties in laminated composites

L'abstract è presente nell'allegato / the abstract is in the attachmen

Characterisation of Glass Fibre Polypropylene and GFPP based Fibre Metal Laminates at high strain rates

Fibre reinforced polymers (FRP) are finding increasing use in structures subjected to high rate loading such as blast or impact. Proper design of such structures requires thorough characterisation of the material behaviour over a range of loading rates from quasi-static to impact. This thesis investigated the quasi-static and impact response of Glass Fibre Polypropylene (GFPP) in compression, bending and delamination. The bending and delamination response of Fibre Metal Laminates (FMLs) based on GFPP and aluminium was also investigated at quasi-static and impact rates. High strain rate (5x10^2 to 10^3 /s) compression tests were conducted on GFPP using a compressive Split Hopkinson Pressure Bar (SHPB) and a Direct Impact Hopkinson Pressure Bar (DIHPB), in the through-thickness and in-plane directions. In both loading directions, the peak stress of GFPP increased linearly with the logarithm of strain rate. For in-plane loading, the failure modes were dominated by localised fibre buckling and kink bands, leading to delamination. The through thickness loading produced macroscopic shear and spreading failure modes. However, both of these failure modes are linked to in-ply fibre failures, due to through thickness compression causing transverse tensile strain. Previous studies of similar materials have not explicitly stated the link between through thickness compression and fibre failure associated with transverse tensile strain. A novel test rig was developed for Three Point bend testing at impact rates. The specimen was supported at the outer points on a rigid impacter and accelerated towards a single output Hopkinson Pressure Bar (HPB), which impacted the specimen at its midspan. Previous impact bend test rigs based on HPBs were limited to testing specimens with deflections to failure up to approximately 1mm, whereas the rig implemented herein measured deflections up to approximately 10 mm. This configuration permits the output HPB to be chosen purely on the magnitude of the expected impact force, which resulted in superior force resolution to configurations used in other studies. The HPB Impact Bend rig was used to test GFPP and aluminium-GFPP FML specimens, at impact velocities ranging from 5 to 12 m/s. The flexural strength of GFPP increased with strain rate, while the flexural response of the FML specimens was relatively insensitive to strain rate. v Several candidate delamination test geometries were investigated at quasi-static displacement rates (1 mm/min), and the Single Leg Bend (SLB) test was identified as suitable for adaptation to higher rate testing. Single Leg Bend delamination tests of both GFPP and FML specimens were performed using the HPB Impact Bend rig, at impact velocities of 6 to 8 m=s. The shape of the force displacement response for the high rate testswas markedly different from the quasi-static tests, for both the GFPP and FML specimens. Finite element (FE) simulation of the quasi-static and impact rate SLB tests on GFPP indicated that the difference was probably due to the interaction of flexural vibrations and stress waves in the specimen and the impacter cross member. The experimental results and FE analysis suggest that the delamination fracture toughness of GFPP decreases slightly as strain rate increases. High rate delamination tests on FML specimens resulted in unstable crack growth

FEASIBILITY ANALYSIS OF STEAM VENTILATION IN SUPERCAVITATION DESIGN

The complete envelopment of a submerged object by a continuous cavity, or supercavity, results in significant reduction of the skin drag acting on the object, allowing for substantial increases in the maximum speeds of underwater devices. The formation of supercavities often requires supplemental ventilation, traditionally by non-condensable gasses, as natural supercavitation occurs at relative speeds between the object and liquid medium that are infeasible for the device to reach without supercavitation itself. The aim of this research is to investigate the feasibility of vaporous ventilation in supercavitation design with the hope of reducing non-condensable ventilation requirements which are inherently limited in their supply for submerged devices. Specifically, the partial or complete replacement of non-condensable gasses with steam for ventilated supercavitation was investigated to determine the effect on cavity development and ventilation requirements. While the use of vaporous ventilation gasses was unfound throughout the extensive literature review, a theoretical analysis which drew from various ventilation scenarios of steam insertion into liquid pools or flows suggested limited potential for the sole use of steam as a ventilation gas. In addition to a theoretical evaluation, cavitator systems were designed and tested to obtain both qualitative and quantitative results. Modest increases in the cavity volume and length were seen for very specific combinations of concurrent ventilation of steam and air relative to air only ventilation. The overall advantages appear extremely limited, however, as the ventilation requirements for steam addition are roughly an order of magnitude larger compared to the required increases of non-condensable ventilation for the production of similar results. Steam alone was shown to be entirely incapable of generating continuous cavitation structures for the range of steam flowrates tested, the upper limit being over three orders of magnitude larger than the critical air ventilation flowrate needed for successful creation of a continuous attached cavity. As such, the advantages of steam ventilation in supercavitation design appear very limited at best when compared to the relative ease of ventilated supercavity development by non-condensable gasses

Seismic Vulnerability of Buried Energy Pipelines in Northern Canada

Permafrost in Canada’s North covers the terrain either continuously or discontinuously. Geological hazards associated with the presence of permafrost are serious barriers against development of the northern hydrocarbon resources. In recent decades, negative effects of geohazards such as frost heave, thaw settlement, slope instability on the safety of northern pipelines are widely studied; however, those of the seismic events are not. During earthquakes, buried pipelines may suffer damage from the induced transient ground deformations (TGD) and/or permanent ground deformations (PGD). While the former is caused by seismic wave propagation, the latter can result from liquefaction, faulting and landslides. This thesis investigates the effects of seismic hazards on the safety of northern pipelines. In discontinuous permafrost regions, the subsurface conditions are complex due to the presence of intermittent scattered frozen areas. Therefore, this case is studied by means of shaking table tests and 2D numerical modelling. It is concluded that the site response at the top of frozen zones is larger than that at the top of unfrozen zones. Consequently, the pipelines in discontinuous permafrost regions are exposed to intermittent differential ground motions during wave propagation. Pipeline response to this type of excitation is investigated using a finite element program developed in Matlab in which soil and pipe nonlinearities, large deformations and cross-sectional ovalization of the pipe are considered. Tensile rupture, local buckling and premature cross-sectional failure are checked and it is observed that the pipes have a margin of safety under TGD. Northern pipelines behaviour subjected to the PGD caused by active-layer detachments, the most common type of landslides in the permafrost regions, is also studied. Considering soil and slope uncertainties and utilizing Monte Carlo technique, probabilistic slope stability analysis is performed first. The probability of exposure to the landslide-caused PGD and the statistical distribution of the PGD zone affecting to the pipelines are computed. The pipeline response to this PGD zone is then calculated utilizing the developed structural analysis program. Finally, effects of PGD zone geometric uncertainties are simulated using Monte Carlo technique and damage functions for the pipelines under PGD are derived

1992 NASA/ASEE Summer Faculty Fellowship Program

For the 28th consecutive year, a NASA/ASEE Summer Faculty Fellowship Program was conducted at the Marshall Space Flight Center (MSFC). The program was conducted by the University of Alabama and MSFC during the period June 1, 1992 through August 7, 1992. Operated under the auspices of the American Society for Engineering Education, the MSFC program, was well as those at other centers, was sponsored by the Office of Educational Affairs, NASA Headquarters, Washington, DC. The basic objectives of the programs, which are the 29th year of operation nationally, are (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate and exchange ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of the participants' institutions; and (4) to contribute to the research objectives of the NASA centers

Shock tunnel studies of scramjet phenomena, supplement 8

Reports by the staff of the University of Oueensland on various research studies related to the advancement of scramjet technology are presented. These reports document the tests conducted in the reflected shock tunnel T4 and supporting research facilities that have been used to study the injection, mixing, and combustion of hydrogen fuel in generic scramjets at flow conditions typical of hypersonic flight. In addition, topics include the development of instrumentation and measurement technology, such as combustor wall shear and stream composition in pulse facilities, and numerical studies and analyses of the scramjet combustor process and the test facility operation. This research activity is Supplement 8 under NASA Grant NAGW-674