Download or read book Multiaxial Stress Studies on Rigid Polyurethane Foam written by Maurice Zaslawsky and published by . This book was released on 1970 with total page 93 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mechanical Response of Polyether Polyurethane Foams Under Multiaxial Stress and the Initial Yielding of Ultrathin Films written by Xiangyu Dai and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In the first part of this thesis, we study the mechanical response of elastic polyether polyurethane (EPP) foams by means of experiments, theory, and modeling. The experiments include five loading cases: uniaxial compression along the rise direction; uniaxial compression along two mutually perpendicular transverse directions; uniaxial tension along the rise direction; shear combined with compression along the rise direction; and hydrostatic pressure combined with compression along the rise direction. We use a commercial series of five EPP foams of apparent densities (mass per unit volume of foam) 50.3, 63.0, 77.0, 162.9 and 220:5 kg/m3. We perform a test for each foam in the series and each loading case. In every test we measure the mechanical response in the form of a stress-strain curve or a force-displacement curve; in several tests we use a Digital Image Correlation (DIC) technique to compute the strain fields on the surface of the specimen. For some loading cases, including uniaxial compression along the rise direction, the mechanical response of the three foams of lower density exhibits a stress plateau. This stress plateau has been commonly interpreted as a manifestation of a bifurcation of equilibrium (Euler buckling of the microstruture of the foam), a global phenomenon that encompasses the entire microstructure of the foam at once. In this interpretation, the plateau stress (i.e., the value of stress on the stress plateau) is the eigenvalue associated with the bifurcation of equilibrium. Nevertheless, our experimental results indicate that a stress plateau is invariably accompanied by heterogeneous, two-phase strain fields, consistent with the occurrence of a configurational phase transition. Thus we argue that the plateau stress is the Maxwell stress associated with the attainment of a limit point (snap-through buckling of a cell of the foam), a local phenomenon which progressively sweeps through the microstructure of the foam. For other loading cases, including uniaxial compression along a transverse direction, the mechanical response does not exhibit a stress plateau, and the stress-strain curves harden monotonically regardless of the density of the foam. The strain fields remain homogeneous, even for the least dense foam. We use our experimental results to calibrate a mean-field model of EPP foams. In this model, a unit cell composed of several bars is cut off from an idealized, perfectly periodic foam microstrusture. The tips of the bars of the cell are subjected to a set of displacements affine with the applied mean deformation gradient, and left to rotate freely. The unit cell is characterized using a few physically meaningful material and geometric parameters whose values may be readily estimated for any given foam. We verify that under uniaxial loading the model predicts configurational phase transitions, stress plateaus, and two-phase fields for low-density foams; a critical point for foams of a critical density; and monotonically hardening stress-strain curves for foams of density higher than the critical density. The critical exponents associated with the critical point are the same as in other mean-field models such as the Van der Walls model of a fluid. With a suitable choice of parameters, the model gives predictions that compare favorably with our experimental results for all loading cases. In particular, the model gives a nonconvex strain energy function where (and only where) the experiments exhibit a stress plateau and two-phase strain fields. We conclude that the mechanical response of EPP foams is dominated at large strains by either one of two mechanisms at the level of a foam cell: snap-through buckling, which leads to nonconvex strain energy functions, stress plateaus, and two-phase strain fields; or bending, which leads to convex strain energy functions, monotonically increasing stresses, and homogeneous strain fields. This conclusion allows us to interpret an extensive series of experiments in which EPP foam specimens are penetrated with a wedge-shaped punch. For low-density foams, we find experimentally that the mechanical response is linear up to a penetration of the punch of about 40% of the height of the specimen. We surmise that the strain field in the specimen consists of a high-strain phase in a region close to the tip, where a phase transition has taken place, and a low-strain phase in a region far from the tip, where the phase transition is yet to take place. The two regions are separated by a sharp interface, where the strain is discontinuous. We use DIC to trace the sharp interface as it grows and sweeps through the specimen during a test. By studying theoretically the self-similar growth of a sharp interface, we predict a linear response within the self-similar regime, in accord with our experimental findings. We then apply the same theory to the case of a conical punch, predict a quadratic response within the self-similar regime, and verify our prediction by performing experiments with a conical punch. We conclude that in the self-similar regime the mechanical response is ruled entirely by geometry and depends only on the dimensionality of the punch and the plateau stress of the low-density foam. In the second part of this thesis, we study the initial yielding of ultrathin metallic films (thickness of a fraction of a micrometer). Recent experiments indicate that in free-standing metallic films of constant grain size the initial yield stress increases as the film becomes thinner, it peaks for a thickness on the order of 100 nm, and then starts to decrease. This reversing (first hardening, then softening) size effect poses two challenges: (1) It cannot be explained using currently available models and (2) it appears to contradict the little-known but remarkable experimental results of J. W. Beams [1959], in which the size effect in bulge tests did not reverse even for a thickness of 20 nm. We show that the reversing size effect can be explained and the contradiction dispelled by taking into account the effect of the surface stress on the initial yielding. We also predict that the mode of failure of a film changes from ductile to brittle for a thickness on the order of 100 nm, in accord with experiments. Our successful application of methods of continuum mechanics to films as thin as 100 times a typical lattice parameter adds to a growing realization of the robustness of these methods at ultrasmall length scales.

Download or read book Equivalent Stress Concept for Limit State Analysis written by Vladimir A. Kolupaev and published by Springer. This book was released on 2018-01-18 with total page 374 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book discusses arbitrary multiaxial stress states using the concept of equivalent stress. It highlights the most useful criteria, which can be applied to various classes of isotropic materials. Due to its simplicity and clarity, this concept is now widely used in component design, and many strength and yield criteria based on the equivalent stress concept have been formulated. Choosing the appropriate criterion for a given material remains the main challenge in applications. The most useful criteria can be applied best when the plausibility assumptions are known. Accordingly, the book introduces fitting methods based on mathematical, physical, and geometrical objective functions. It also features a wealth of examples that demonstrate the application of different approaches in modeling certain limit behaviors.

Download or read book A study of rigid polyurethane foam written by V. A. Grasso and published by . This book was released on 1977 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1971 with total page 1310 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 892 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Proceedings of the American Society for Composites Seventeenth Technical Conference written by C. T. Sun and published by CRC Press. This book was released on 2002-10-24 with total page 1685 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Metal Foams written by Nihad Dukhan and published by DEStech Publications, Inc. This book was released on 2013 with total page 459 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book offers the first full-scale technical treatment of an important class of engineered porous materials: metal foams. Written by a team of metal foam experts from around the world, the volume offers new, as well as fundamental, information on all aspects of metal foams, including their theory, manufacture, structure-property relationships and applications. The book explains microscopy and modeling tools that enhance the prediction and determination of metal foam properties related to fluid flow, heat transfer, sound absorption and failure analysis. Attention is given to the many techniques for manufacturing and testing metal foams and to how their microstructure can be controlled to create custom properties for applications in acoustics, bone implants, heat sinks, lightweighting and crash protection. The text is sufficiently detailed to offer guidance to design and development engineers, and yet is basic enough to be used as a textbook or reference by students of materials science, mechanical, structural or chemical engineering requiring an introduction to the subject.

Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1973 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fracture and Strength of Solids VI written by Ichsan Setya Putra and published by Trans Tech Publications Ltd. This book was released on 2006-03-15 with total page 1600 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volume is indexed by Thomson Reuters CPCI-S (WoS). Fracture, Fatigue and Strength are some of the most important properties of engineering materials.

Download or read book Proceedings of the Society for Experimental Stress Analysis written by Society for Experimental Stress Analysis and published by . This book was released on 1973 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vol. 1, no. 1 contains Proceedings of the 17th (or the last) Eastern Photoelasticity Conference.

Download or read book American Sociey of Composties Fifteenth International Conference written by Amer Society Composi and published by CRC Press. This book was released on 2000-09-26 with total page 1258 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Accessions of Unlimited Distribution Reports written by and published by . This book was released on 1970-12-04 with total page 52 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Cellular Solids written by Lorna J. Gibson and published by Cambridge University Press. This book was released on 1999-07-22 with total page 536 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this new edition of their classic work on Cellular Solids, the authors have brought the book completely up to date, including new work on processing of metallic and ceramic foams and on the mechanical, electrical and acoustic properties of cellular solids. Data for commercially available foams are presented on material property charts; two new case studies show how the charts are used for selection of foams in engineering design. Over 150 references appearing in the literature since the publication of the first edition are cited. The text summarises current understanding of the structure and mechanical behaviour of cellular materials, and the ways in which they can be exploited in engineering design. Cellular solids include engineering honeycombs and foams (which can now be made from polymers, metals, ceramics and composites) as well as natural materials, such as wood, cork and cancellous bone.

Download or read book A Study of Rigid Polyurethane Foam Final report written by United States. National Highway Traffic Safety Administration and published by . This book was released on 1977 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mechanics of Plastics and Plastic Composites 1995 written by Mary Cunningham Boyce and published by . This book was released on 1995 with total page 454 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Use of Plastics and Plastic Composites written by American Society of Mechanical Engineers. Winter Annual Meeting and published by . This book was released on 1993 with total page 696 pages. Available in PDF, EPUB and Kindle. Book excerpt: