Showing papers in "Experimental Mechanics in 1965"
1,005 citations
TL;DR: In this paper, the strength of anisotropic composite materials subjected to any state of combined stress, predicted from basic strength characteristics of unidirectional layer, is estimated from the basic strength of composite materials.
Abstract: Strength of anisotropic composite materials subjected to any state of combined stress, predicted from basic strength characteristics of unidirectional layer
503 citations
TL;DR: In this paper, the current status of knowledge regarding the dynamic behavior of crystalline materials in terms of athermal, thermally activated, viscous damping, and relativistic motion of dislocations is presented.
Abstract: A brief summary is presented on the current status of knowledge regarding the dynamic behavior of crystalline materials in terms of athermal, thermally activated, viscous damping, and relativistic motion of dislocations. It is shown that dislocation concepts have contributed substantially to a better and more unified rationalization of the dynamic behavior of crystalline materials than heretofore possible. Particular emphasis is given to the need for a more complete theoretical understanding of dislocation mechanics. Also, the requirements for more detailed and better experiments are expressed particularly for dislocation-velocity determinations in the viscous damping and relativistic ranges of conditions.
104 citations
TL;DR: In this paper, the authors generalize the optical law that relates the displacement field to the fringes of moire patterns and apply a discontinuous relationship to the points of maximum and minimum light intensity.
Abstract: The objective of this paper is to generalize the optical law that relates the displacement field to the fringes of moire patterns. Until now, a discontinuous relationship has been applied. Displacements that are equal to an integral number of times the master grid pitch or half the master grid pitch are related to the points of maximum and minimum light intensity, respectively.
90 citations
TL;DR: In this article, the authors describe a simple testing unit, developed at the Technical University of Denmark and described in the present paper, which is used for dynamic testing at high strain rates.
Abstract: Some of the problems regarded as inherent in materials testing at high strain rates are associated with inertia effects, both in the loading mechanism and in the specimen itself. In fact, it has generally been difficult to ensure a homogeneous and uniaxial strain field. Some of these problems encountered in dynamic testing have, however, been circumvented in a simple testing unit, developed at the Technical University of Denmark and described in the present paper.
90 citations
TL;DR: In this paper, the complete state of strain throughout an extended field can be determined from a single photograph by the moire grid-analyzer method, where two families of moire fringes appear simultaneously, providing displacements inx andy directions throughout the field.
Abstract: The complete state of strain throughout an extended field can be determined from a single photograph by the moire grid-analyzer method. Grids are used for the active, or specimen screen, and for the rigid analyzer screen. Hence, two families of moire fringes appear simultaneously, providing displacements inx andy directions throughout the field.
47 citations
TL;DR: In this paper, a testing machine is described which is capable of applying biaxial, tension-torsion loading to thin-walled tubular specimens over a wide range in loading rates.
Abstract: The development of generalized constitutive equations for materials requires additional experimental data. A testing machine is described which is capable of applying biaxial, tension-torsion loading to thin-walled tubular specimens over a wide range in loading rates. Both components of the load are independently controlled. The objective is to obtain information on the effect of the rate of loading on viscoplastic or viscoelastic behavior of materials. Some preliminary data are given on the effect of loading rate on the yielding of mild steel.
42 citations
40 citations
TL;DR: In this paper, a general theory is formulated whereby the properties of a laminated anisotropic composite can be predicted once the material properties, the thickness and the orientation of each unit ply are known.
Abstract: The present investigation is concerned with the development of a theoretical basis for determining the elastic moduli of laminated anisotropic materials within the framework of the theory of plates and shells, and the establishment of sound experimental procedures for the confirmation of the predicted results. A general theory is formulated whereby the properties of a laminated anisotropic composite can be predicted once the material properties, the thickness and the orientation of each unit ply are known. Treated in detail are the cross-ply and angle-ply laminates, these configurations being of increasing importance to designers and analysts of filament-wound materials. Laminated materials of this type may, depending on lamination parameters, exhibit coupling between in-plane strain and bending or twisting curvature which must be considered in the analysis and testing of such materials. Based on an understanding of the predicted mechanical behavior, an experimental program is designed, using glass-filament-reinforced resin cross-ply and angle-ply plates and cylindrical pressure vessels as test specimens, which confirms the validity of the theory and presents experimental data heretofore not available.
39 citations
TL;DR: In this article, a condensed general method containing Ferry's modulus or compliance reduction scheme, the time-temperature superposition principle and the Gauss error integral representation is presented.
Abstract: Some principles ans laws, expressing the mechanical and optical behavior of linear viscoelastic materials, are reviewed. The mechanical properties of the polymers in the transition region may be represented by a condensed general method containing Ferry's modulus or compliance-reduction scheme, the time-temperature superposition principle and the Gauss error integral representation. The optical behavior of high polymers is expressed by the stress- and strain-optical coefficients in creep or relaxation, which relate birefringence to stresses or strains. It was recently shown experimentally that, instead of a pair of independent linear differential operator relations, which characterize the mechanical properties of the viscoelastic materials, only one operator relation is needed and the initial value of another at the glassy or rubbery state. Then, a single test is sufficient for the complete determination of the mechanical and optical viscoelastic behavior, provided the value of another elastic constant at the glassy or rubbery state is also determined and the variation of birefringence with time is simultaneously measured with the mechanical-characteristic quantities of the material.
28 citations
TL;DR: In this article, the results of buckling tests on cylinders heated uniformly along axial strips are presented and discussed, and a comparison between theoretical and experimental results is made between them.
Abstract: The results of buckling tests on circular cylinders heated uniformly along axial strips are presented and discussed. Calculations of critical temperature based upon the small-deflection theory for thin circular cylindrical shells are included and a comparison is made between theoretical and experimental results. Cylinders heated along axial strips of given widths have a theoretically predicted behaivor which corresponds reasonably well to the behavior obtained by experiment. Curves are included showing the variation of critical temperature with respect to heated axial-strip width.
TL;DR: In this paper, a photoreading device is described, which combined with the displacement-light-intensity law yields an accuracy beyond the limits so far obtained by the usual method of handling moire data.
Abstract: The object of Part 2 of this paper is to show applications of the displacement-light-intensity law derived in Part 1. A photoreading device is described, which combined with the new theory, yields an accuracy beyond the limits so far obtained by the usual method of handling moire data. Three tests are presented: one test is used as an illustration of the applied procedures, the other two for comparison with theoretical results. These tests show that the theory is useful and that strains can be obtained with an accuracy impossible to achieve by the discrete point method of analysis. Relatively coarse grids of 300 lines/in. are used for these tests.
TL;DR: A theoretical analysis of the stresses induced in thin elastic strips which are bent (by uniform bending moments) into arcs with substantially constant radii of curvatures is made in this paper. But this analysis assumes that the elastic strips have a uniform curvature.
Abstract: A theoretical analysis is made of the stresses induced in thin elastic strips which are bent (by uniform bending moments) into arcs with substantially constant radii of curvatures. Stresses determined experimentally on aluminum and steel strips agree very well with the theory.
TL;DR: In this article, a numerical procedure is developed, based on the trapezoidal rule, which determines the transverse deflections from the readings of strain gages mounted to the top and bottom surface of a rectangular plate subjected to large longitudinal curvatures.
Abstract: The purpose of this paper is to show that the readings from strain gages can be used effectively to compute small transverse deflections in a rectangular plate and, further, show that the theory developed by Lamb for the rectangular-plate problem agrees with experiment. A numerical procedure is developed, based on the trapezoidal rule, which determines the transverse deflections from the readings of strain gages mounted to the top and bottom surface of a rectangular plate subjected to large longitudinal curvatures. It is shown using the strain-gage technique that experiment agrees with Lamb's theory forb
2
/Rt ratios up to 50.
TL;DR: In this paper, the authors describe an experimental technique by which contours of equal resolved curvature can be defined by the superposition of two Salet-Ikeda slope photographs.
Abstract: In two previous papers describing the Salet-Ikeda slope contouring method and the Martinelli-Ronchi point-by-point curvature method, definition of curvature over the whole field of a flexed elastic plate was the ultimate objective. This paper describes briefly an experimental technique by which contours of equal resolved curvature can be defined by the superposition of two Salet-Ikeda slope photographs.
TL;DR: In this paper, a numerical procedure is developed, based on the trapezoidal rule, which determines the transverse deflections from the readings of strain gages mounted to the top and bottom surface of a rectangular plate subjected to large longitudinal curvatures.
Abstract: The purpose of this paper is to show that the readings from strain gages can be used effectively to compute small transverse deflections in a rectangular plate and, further, show that the theory developed by Lamb for the rectangular-plate problem agrees with experiment.A numerical procedure is developed, based on the trapezoidal rule, which determines the transverse deflections from the readings of strain gages mounted to the top and bottom surface of a rectangular plate subjected to large longitudinal curvatures. It is shown using the strain-gage technique that experiment agrees with Lamb's theory forb2/Rt ratios up to 50.
TL;DR: In this article, a method for determining the surface strain at all points on the surface of a structure was developed, where narrow epoxy-resin strips on a thin film are cemented to the surface surface of the body under study.
Abstract: An experimental method has been developed for determining the strains at all points on the surface of a structure. Narrow epoxy-resin strips on a thin film are cemented to the surface of the body under study. Photoelastic studies show that the birefringent pattern of these strips is dependent only on the longitudinal strain parallel to their axes. When the strips are used in conjunction with a continuous photoelastic coating, the surface strain can be determined at all points from direct observation of the fringe patterns.
TL;DR: In this paper, a rigid-vinyl plastic monocoque domes subjected to external pressure loads were constructed and tested under a variety of conditions, including external pressure and temperature.
Abstract: Fabrication, testing and experimental results for rigid-vinyl plastic monocoque domes subjected to external pressure loads
TL;DR: In this paper, the authors simplify the integral equation for the impact force due to the transverse impact by calculating separately the series of the eigenfunctions and eigenfrequencies.
Abstract: The tests of several scientific workers have shown that the central maximum loading by transverse impact on beams is independent of the boundary conditions In this case, the length of the beam is so long that the elastic waves reflected from the supports return to the point of contact after the central peak stress has developed Now, by these conditions it is possible to simplify the integral equation for the impact force due to the transverse impact The simplification is realized by calculating separately the series of the eigenfunctions and the eigenfrequencies Introducing a special reference time and dimensionaless variables, the altered integral equation may be treated in a relative simple way by a computer The results given in dimensionless form, namely the impact force and the central bending strain as a function of time, allow quickly the calculation of the mechanical loading The magnitudes of the impact values also depend on a parameter which may be signified as a characteristic value of the transverse impact This parameter contains the impact velocity, the striking mass, the Hertz constant and a parameter of the beam This simplified theory of transverse impact was verified by measurements with strain gages, displacement device and PhotoStress method The contact time was also measured and the data of the tests were changed, ie, the velocity of the striking mass and the magnitude of the mass In order to obtain the axial central strain at the lower side of the beam, the added action of the impact force must be taken into account according to the theory of Wilson-Stokes Using the normalized curves of data of the impact, it is possible for untrained engineers to calculate the mechanical loading
TL;DR: In this article, a three-dimensional photothermoelastic study of stresses generated around the edge of a hole in a flat unrestrained plate subjected to a thermal shock uniformly applied to one face of the plate was performed.
Abstract: This paper contains a three-dimensional photothermoelastic study of stresses generated around the edge of a hole in a flat unrestrained plate subjected to a thermal shock uniformly applied to one face of the plate. The approach taken is experimental in nature, utilizing a newly developed three-dimensional, non-destructive photoelastic technique. An extrapolation procedure is formulated in order to determine transient fringe orders at the thermally shocked surface. For the case considered, the thermal-stress-concentration factor at the edge of the hole was found to be 1.28.
TL;DR: In this article, thermal stresses were simulated in photoelastic models by a mechanical-prestraining method, which allowed the study of complex stress distributions arising from simple thermalexpansion conditions.
Abstract: Several experiments are reported in which thermal stresses were simulated in photoelastic models by a mechanical-prestraining method. This method permitted the study of complex stress distributions arising from simple thermal-expansion conditions. The validity of the method is demonstrated by providing a comparison between theoretical and experimental results obtained for a fundamental disk problem. The usefulness of the method is illustrated by presenting some results of a tube-sheet experiment pertaining to a difficult engineering problem. Additional applications are described to indicate the variety of problems that may be studied by the prestraining method.
TL;DR: The use of diffraction gratings as integral parts of the surfaces of flat metal specimens has led to modification of the method of Bell and to the investigation of strain fields by studying diffraction phenomena as discussed by the authors.
Abstract: The development of means for producing small, separate, plane diffraction gratings as integral parts of the surfaces of flat metal specimens has led to modification of the method of Bell and to the investigation of strain fields by study of diffraction phenomena. Choice of a particular diffraction-strain relationship and the use of master gratings in conjunction with diffraction gratings to be used as strain gages permits use of simple optical instrumentation. The diffraction phenomena from multiple gages at the same orientation may be photographed simultaneously during loading for subsequent analysis, and instrumentation in the form employed permits resolving strain increments of magnitude 0.0008 in the range 0.0030 to 0.030.
TL;DR: In this paper, the elastic stress-concentration factors for countersunk holes were determined by the birefringent-plastic-coating method on plain-hole specimens, and the stresses were compared with theoretical values.
Abstract: This paper describes a method of determining the elastic stress-concentration factors for countersunk holes. Local stresses were determined by the birefringent-plastic-coating method on plain-hole specimens, and the stresses were compared with theoretical values. Local stresses were then determined by the same method at all points around countersunk holes except at the base of the countersink. A series of fatigue tests was conducted on groups of plain-hole and countersunkhole specimens, and the elastic stress-concentration factors for the base of the countersinks were determined from the results.
TL;DR: In this paper, the results of mechanical and optical measurements in plasticized polyvinyl chloride under conditions of creep and relaxation at room temperature are described. But the results are limited to the case of a single sample.
Abstract: This paper describes the results of mechanical and optical measurements in plasticized polyvinyl chloride under conditions of creep and relaxation at room temperature. It covers one task of a broader investigation aimed at developing experimental methods for viscoelastic stress analysis.
TL;DR: In this paper, two-and three-dimensional photoelasticity methods to stress and strain analyze propellant-grain models are reviewed and the advantages and limitations of two-dimensional simulations of the threedimensional problems are studied in detail.
Abstract: Two- and three-dimensional photoelasticity methods to stress and strain analyze propellant-grain models are reviewed. Pressure, restrained shrinkage and transient thermal loadings are considered. The advantages and limitations of two-dimensional simulations of the three-dimensional problems are studied in detail.
TL;DR: In this paper, the performance characteristics of bonded resistance strain gages in high-temperature and nuclear-radiation environments are discussed, and the methods used to minimize errors induced by the extreme environments are fully discussed.
Abstract: This paper covers the performance characteristics of bonded resistance strain gages in high-temperature and nuclear-radiation environments. Typical electrical properties of ceramic-bonded strain gages are given for various environmental conditions. The methods used to minimize errors induced by the extreme environments are fully discussed.
TL;DR: In this article, a linear pressure-strain response was obtained for gages mounted on convex and concave specimens subjected to hydrostatic pressures to 140 ksi, where flat surfaces only were considered.
Abstract: The present investigation was undertaken to determine whether a linear pressure-strain response could be obtained for gages mounted on convex and concave specimens subjected to hydrostatic pressures to 140 ksi. This is an extension of a previously reported work where flat surfaces only were considered.
TL;DR: In this article, the velocity profiles in an expanding fluid jet were obtained from analysis of birefringence measurements over the flow field, and a new method of photoviscous analysis to determine the pertinent flow information from isochromate data alone was developed as part of the investigation.
Abstract: This paper presents experimental measurements of the velocity profiles in an expanding fluid jet. The data were obtained from analysis of birefringence measurements over the flow field. A new method of photoviscous analysis to determine the pertinent flow information from isochromate data alone was developed as part of the investigation.
TL;DR: In this paper, a stress-wave technique for determining the dynamic tensile strength of brittle materials is discussed, and the results of experiments with bar specimens of aluminum oxide are presented.
Abstract: A stress-wave technique for determining the dynamic tensile strength of brittle materials is discussed. The results of experiments with bar specimens of aluminum oxide are presented. Experimental evidence to verify the reliability of the state of dynamic tensile stress resulting from the reflection of a longitudinal stress wave from a free boundary is included. Values of dynamic tensile strength of aluminum oxide are tabulated and compared with values obtained using the same material and two different static methods.