[ { "id": "authors:bhtq6-m5c35", "collection": "authors", "collection_id": "bhtq6-m5c35", "cite_using_url": "https://resolver.caltech.edu/CaltechGALCITSM:GALCITSM94-5", "type": "monograph", "title": "Deformation Measurements at the Sub-Micron Size Scale: II. Refinements in the Algorithm for Digital Image Correction", "author": [ { "family_name": "Vendroux", "given_name": "G.", "clpid": "Vendroux-G" }, { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" } ], "abstract": "Improvements are proposed in the application of the Digital Image Correlation method, a technique that compares digital images of a specimen surface before and after deformation to deduce its sureface (2-D) displacement field and strains. These refinements, tested on translations and rigid body rotations were significant with regard to the computer efficiency and covergence properties of the method. In addition, the formulation of the algorithm was extended so as to compute the three-dimensional surface displacement field from Scanning Tunneling Microscope tomographies of a deforming specimen. The reolsution of this new displacement measuring method at the namometer scale was assessed on translation and uniaxial tensile tests and was found to be 4.8 nm for in-plane displacement components and 1.5 nm for the out-of-plane one spanning a 10 x 10 \u03bcm area.", "doi": "10.7907/pedw-pd07", "publisher": "California Institute of Technology", "publication_date": "1994-04" }, { "id": "authors:2s6rf-q1x14", "collection": "authors", "collection_id": "2s6rf-q1x14", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:GALCITSM94-5a", "type": "monograph", "title": "Submicron Deformation Field Measurements II: Improved Digital Image Correlation", "author": [ { "family_name": "Vendroux", "given_name": "G.", "clpid": "Vendroux-G" }, { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" } ], "abstract": "This is the second paper in a series of three devoted to the applicaiton of Scanning Tunneling Microscopy to mechanics problems. In this paper improvements to the Digital Image Correlation method are outlined, a technique that compares digital images of a specimen surface before and after deformation to deduce its (2-D) surface displacement field and strains. The necessity of using the framework of large deformation theory for accurately addressing rigid body rotations to reduce associated errors in the strain components is pointed out. In addition, the algorithm is extended to compute the three-dimensional surface displacement field from Scanning Tunneling Microscope data; also, significant improvements are achieved in the rate as well as the robustness of the convergence. For Scanning Tunneling Microscopy topographs the resolution yields 4.8 nm\nfor the in-plane and 1.5 nm for the out-of-plane displacement components spanning an area of 10 \u03bcm x 10 \u03bcm.", "doi": "10.7907/zvy1-mb79", "publisher": "California Institute of Technology", "publication_date": "1994" }, { "id": "authors:4vxp2-b1x37", "collection": "authors", "collection_id": "4vxp2-b1x37", "cite_using_url": "https://resolver.caltech.edu/CaltechGALCITSM:GALCITSM80-18", "type": "monograph", "title": "Hygroviscoelasticity of the Human Intervertebral Disc: Final Report", "author": [ { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" } ], "abstract": "In order to gain an improved understanding of the behavior of human intervertebral disc material under various kinds of loads the viscoelastic properties of small specimens excised from human L4-L5 discs were examined. Excisions were made from donated spine segments procured a few hours after death and then frozen. Material examined was in the form of single lamellar specimens as well as specimens containing several lamellae. \n\nTensile relaxation tests were performed on single lamellae prepared such that the collagen fibers were a) aligned with the tension axis, b) normal to the tension axis and c) at an angle of about 30[degrees] with that axis. The multi-lamellar specimens were excised from the disc such that one set produced the tensile axis to run parallel to the disc circumference (surrounding the spinal axis) while another set caused the tensile axis to run parallel to the spinal axis. \n\nIt was found early in the study that the water content of the disc material has a profound effect on its mechanical response. Consequently the diffusion and swelling characteristics of the material in different water environments were studied. Primarily air of differing relative humidity and various concentrated solutions of NaCl were used to provide for different water concentrations in the material. \n\nFor the relaxation studies the same environments were used. This allowed achieving water concentrations ranging from virtually dry to in-vivo conditions. \n\nThe main findings of this work are: \n\n1) Water affects the relaxation time in a sensitive way. A few percent change in water content can change the relaxation time by an order of magnitude or more. This fact is important when one is concerned with laboratory testing without being able to control the water content at all times. \n\n2) Diffusion is a surprisingly slow process taking place over several hours (2-3) in specimens only 1/2 mm thick. The\namount of water take-up is controlled by the environment (distilled water destroys samples into fissures) and by constraints offered by the fiber structure and the stresses it engenders (see point 5) below). \n\n3) The stiffness of the disc material is on the order of 3 to 10 x 10^-6 N/m^2; relaxation occuring, on the whole rather slowly, i.e., on the order of 10% per decade. The relaxation modulus at right angles to the collagen fibers is about 1/3 that of the modulus along the fiber direction. \n\n4) The relaxation modulus of multi-layer specimens cut from the disc in a circumferential and a spine-axial direction are very nearly the same; the modulus for the circumferential material is slightly higher. The consequence of this would be that although one would expect a markedly anisotropic behavior of the disc material on the basis of its fiber and lamellar construction, the disc material does not deviate very strongly from isotropic response. (Isotropy as-referred to a plane that is tangent to the disc perimetric surface.) \n\n5) Stress affects the equilibrium concentration of water in the material. The implication - and test result - is that once the stress has changed the equilibrium of water content with the environment is disturbed and the concentration changes. That change, in turn, causes a change in relaxation behavior such that tensile stresses cause an acceleration of relaxation or creep (softening), while compression would cause the opposite affect (hardening). The material responds thus to stress as a system that is open to the environment.", "doi": "10.7907/qx6y-c525", "publisher": "California Institute of Technology", "publication_date": "1980-07" }, { "id": "authors:6p33b-x9e56", "collection": "authors", "collection_id": "6p33b-x9e56", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20141114-131259517", "type": "monograph", "title": "The Incorporation of Bending into the Buckling Delamination Analysis: Informal Progress Report No. 3", "author": [ { "family_name": "Chai", "given_name": "H.", "clpid": "Chai-H" }, { "family_name": "Babcock", "given_name": "C. D.", "clpid": "Babcock-C-D" }, { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" } ], "abstract": "In a previous report a one dimensional model of buckling-delamination in a column was summarized. The main assumption made in that report was that the unbuckled portions of the column can be assumed to remain straight. The purpose of this report is to investigate the\nmore general problem in which bending effects are taken into account. We deal here with the case of a single off center delamination in a column. (The case of multi-delaminations in a column can be worked out too\nunder slight modifications.) Following the general procedure outlined in previous reports, consider the column of unit width shown in fig, la, State I represents the unstressed column while state I1 denotes the\naxially and uniformally compressed column. State III differs from II by allowing the delamination to buckle. Our aim here is to find an\nexpression for the strain energy release rate of state III.", "doi": "10.7907/jvgn-3580", "publisher": "California Institute of Technology", "publication_date": "1979-11" }, { "id": "authors:3c3ef-57s65", "collection": "authors", "collection_id": "3c3ef-57s65", "cite_using_url": "https://resolver.caltech.edu/CaltechGALCITSM:GALCITSM77afosr77-3139", "type": "monograph", "title": "Viscoelastic Behavior of the Human Intervertebral Disc Under Consideration of Moisture Migration", "author": [ { "family_name": "Panagiotacopulos", "given_name": "N. D.", "clpid": "Panagiotacopulos-N-D" }, { "family_name": "Bloch", "given_name": "R.", "clpid": "Bloch-R" }, { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" }, { "family_name": "Harvey", "given_name": "P.", "clpid": "Harvey-P" }, { "family_name": "Patzakis", "given_name": "M.", "clpid": "Patzakis-M" } ], "abstract": "The human intervertebral disc is a highly inhomogeneous fiber composite pressure vessel. If damaged in the post-infant stage, the disc does not repair and may need surgical correction. Diagnosis of whether a disc is damaged is difficult at best and, at this time, involves invasive techniques which are not free of danger (injection of x-ray opaque liquids). Starting from a desire to develop a noninvasive diagnostic technique based on x-ray and computer aided image enhancement, we became interested in the mechanical properties of the disc. These would be important in gaging the x-ray detected deformations of the disc under various loads. During the course of this work we became aware of another need of diagnostics related to estimating the proclivity of an intact disc to sustain damage under unusual loads. It turns out that the water content of the disc material dominates its mechanical behavior. Since modern medical equipment such as the EMI-x-ray body-scanner may record quantitatively the water content of the internal body organs, the possibility exists to gage in-vivo water content measurements with the mechanical performance of discs. \n\nBecause the layers of the disc's annulus fibrosous are so thin, we have had difficulty in preparing single-layer specimens. So far, we have worked mainly with three-layer specimens. That test geometry has been sufficient to establish several important aspects of the mechanical properties. \n\nWe find that the relaxation behavior is very sensitive to moisture content. Accordingly we have worked with carefully controlled environments including saline solutions claimed to represent body conditions. A major difficulty in obtaining repeatable results is obtaining straight test specimens and holding them in the clamps of the testing apparatus. If moisture and temperature conditioning was repeated without reclamping the specimen, reasonably repeatable results were obtained. No aging was observed after repeated drying and moisturizing cycles. \n\nWe also found that water diffuses slowly in the layers. The water apparently acts similar to the solvent in a polymer, effecting a change in the relaxation times. Increasing water content causes shortening of relaxation times, drying having the opposite effect. Upon controlling the water content of the specimen we are thus able to measure the relaxation behavior in various time domains. Data covering a wide spectrum of relaxation times is presented which includes all of the time scales experienced by the human body. This mechanical characterization gives us an estimate of how discs respond to different rates of deformation and loading conditions. \n\nIt is of interest to note that with age (past age 30) the moisture content of the human disc decreases (possible other changes involving increased cross-link density of the mucopolysaccharides as well as an exchange of mucopolysaccharides for collagen). As a result one would expect the human intervertebral disc to react more stiffly with increasing age under nearly constant speeds of motion. Combining this observation with the changes in the vigor of motion/muscle activity as a function of age allows a tentative explanation of the statistic that the largest incidence of disc problems occur around age 40-50.", "doi": "10.7907/ynhb-7j56", "publisher": "California Institute of Technology", "publication_date": "1977-06-27" }, { "id": "authors:5dasw-zyj96", "collection": "authors", "collection_id": "5dasw-zyj96", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20150604-135847602", "type": "monograph", "title": "Fundamental Studies Relating to Systems Analysis of Solid Propellants, January 1, 1960-May 31, 1960", "author": [ { "family_name": "Blatz", "given_name": "P. J.", "clpid": "Blatz-P-J" }, { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" }, { "family_name": "Schapery", "given_name": "R. A.", "clpid": "Schapery-R-A" }, { "family_name": "Williams", "given_name": "M. L.", "clpid": "Williams-M-L" } ], "abstract": "Previous reports of this series have attempted to\ndefine some of the important parameters affecting structural\nintegrity of solid propellant rocket grains. Three general\nareas have been discussed, namely material properties,\nanalytical procedures, and criteria for mechanical failure.\n\nThis particular report is devoted to failure criteria,\nincluding both limiting deformation and fracture. First of all, the characteristic material properties of filled and unfilled elastomers are described, followed by a brief description of current and proposed tests which can be conducted to obtain experimental information relating to these characteristics in such a form that they can be incorporated in structural integrity analyses. In particular, the necessity for multi-axial\ntests is stressed in conjunction with minor requirements\nfor new experimental equipment.\n\nThe selection of appropriate fracture criteria is discussed.\nMost progress, however, can be reported only in criteria for\nunfilled elastomers for small and large strains where it appears a distortion strain energy density may be used. It is necessary to delay any really definitive remarks upon filled elastomers or actual grain composites, and subsequent use with cumulative\ndamage analyses, until additional experimental data for propellants is forthcoming.", "doi": "10.7907/6wsw-zw77", "publisher": "California Institute of Technology", "publication_date": "1960-06-15" }, { "id": "authors:ge1wj-66q37", "collection": "authors", "collection_id": "ge1wj-66q37", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20151203-165233805", "type": "monograph", "title": "Fundamental Studies Relating to Systems Analysis of Solid Propellants, October l, 1959-December 31, 1959", "author": [ { "family_name": "Blatz", "given_name": "P. J.", "clpid": "Blatz-P-J" }, { "family_name": "Knauss", "given_name": "W. G.", "clpid": "Knauss-W-G" }, { "family_name": "Schapery", "given_name": "R. A.", "clpid": "Schapery-R-A" }, { "family_name": "Stimpson", "given_name": "L. D.", "clpid": "Stimpson-L-D" }, { "family_name": "Williams", "given_name": "M. L.", "clpid": "Williams-M-L" } ], "abstract": "Previous reports of this series have attempted to define some of the important parameters affecting the structural integrity of solid propellant rocket grains. Three general areas have been discussed, namely material properties, analytical procedures, and criteria for mechanical\nfailure.\n\nThis particular report is devoted to a more detailed examination of the properties of a filled viscoelastic resin, and their representation by appropriate mechanical models. In addition, a comparison of two methods of computing viscoelastic strains in a pressurized cylinder is\npresented.\n\nIn the category of material properties, linear viscoelastic model theory is reviewed, and certain important relations among sets of experimental data are deduced. A justification for the application of this theory is provided by the analytic representation of available dynamic\ndata in terms of a well-known distribution function. Since the inception of this work additional experimental data on propellants has become available.\n\nIn the category of analytical procedures, the usual approach of representing material properties by a four-element model, as determined from the dynamic data in a limited frequency range, is compared with the\nmore sophisticated Fourier transform method in which the entire frequency range is utilized. The two approaches are applied to calculate the viscoelastic hoop strain at the inner boundary of an internally pressurized infinitely\nlong hollow cylinder subjected to a ramp-type pressure pulse. In this example, the dilatation is assumed elastic or frequency independent and the distortion viscoelastic.\n\nIn the following quarter, primary effort will be devoted to the determination of a criterion for mechanical failure of propellants. Two steps are involved. One is the analytical representation of ultimate strain as a function of temperature on strain rate by means of a mechanical model. In addition to the usual distribution of relaxation (or retardation) times, this model will be supplied with a distribution of ultimate strain. Step two involves\nthe choice of a suitable criterion for compounding ultimate strain or ultimate stress components into a single parameter, which, when exceeded at a given\nrate and temperature, denotes the onset of fracture or mechanical failure.", "doi": "10.7907/0sxn-1k84", "publisher": "California Institute of Technology", "publication_date": "1960-01-15" } ]