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Showing papers in "Experimental Mechanics in 1973"


Journal ArticleDOI
TL;DR: In this article, a series of experiments has been conducted, utilizing sheet explosive opplied to clamped aluminum beams, with a neoprene buffer, and three damage modes are identified, which respecitively are major inelastic deformation, tearing at the extreme fiber, and transverse shear at the support.
Abstract: A series of experiments has been conducted, utilizing sheet explosive opplied to clamped aluminum beams, with a neoprene buffer. As the load is monotonically increased, three damage modes are identified, which respecitively are major inelastic deformation, tearing at the extreme fiber, and transverse shear at the support.Satisfactory correlation is reported for the extent of inelastic deformation using a lumped parameter, finite-difference code; thresholds for tearing and shear failure based on empirical criteria are presented. Using a Timoshenko beam theory, the shear threshold appears to be dependent on the section velocity, rather than upon the shear stress.

252 citations


Journal ArticleDOI
TL;DR: In this article, a medium strain-rate machine and a split-Hopkinson-bar apparatus are used in conducting the experiments and the temperature rise developed during deformation is also measured by using a thermocouple.
Abstract: Polymethylmethacrylate, cellulose acetate butyrate, polypropylene and nylon 6–6 have been characterized in compression at various strain rates from 10−4 s−1 to 103 s−1 at room temperature. A medium strain-rate machine and a split-Hopkinson-bar apparatus are used in conducting the experiments. The temperature rise developed during deformation is also measured by using a thermocouple. All four materials tested definitely show a viscous effect at the beginning of the deformation and a plastic flow follows thereafter. Test results also indicate that the temperature rise developed during deformation cannot be neglected in determining the dynamic response of those materials investigated in this study.

159 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed description is presented on the procedure of testing, preparation of specimen, the required tools and measuring devices and working conditions, and a standard procedure to carry out such measurement does not exist in the published literature.
Abstract: The measurement of residual stresses by the sectioning method has been used for decades to measure residual stresses in structural members. This method has proven itself adequate, accurate and economical if proper care is taken in the preparation of the specimen and the procedure of measurement. However, a standard procedure to carry out such measurement does not exist in the published literature. In this paper, a detailed description is presented on the procedure of testing, preparation of specimen, the required tools and measuring devices and working conditions.

143 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the mechanical properties of glass-fiber-reinforced epoxy plates subjected to high rates of strain on a specially designed impact-loading machine propelled by explosives.
Abstract: The object of this investigation is to establish experimentally the mechanical properties, and the mode of failure of glass-fiber-reinforced epoxy plates subjected to high rates of strain (30,000 in./in./min), in the direction of the fibers, on a specially designed impact-loading machine propelled by explosives. The results are correlated with those obtained by testing glass-fiber-reinforced epoxy plates subjected to various low rates of strain (0.0265 in./in./min, 0.66 in./in./min and 26.5 in./in./min).

94 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental method is described which can measure the direction and magnitude of residual and applied stress in metals using optical interference to measure the permanent surface deformation around a shallow spherical indentation in a polished area on the metal.
Abstract: An experimental method is described which can measure the direction and magnitude of residual and applied stress in metals. The method uses optical interference to measure the permanent surface deformation around a shallow spherical indentation in a polished area on the metal specimen. The deviation from circularly symmetrical surface deformations is measured at known values of applied stress in calibration specimens. This deviation from symmetry can then be used to determine the direction and magnitude of tensile residual stress in specimens of the same material. Determination of compressive residual stress is more limited.

48 citations


Journal ArticleDOI
TL;DR: In this paper, the anisotropic states of stress, strain and fracture of a glass-epoxy plate containing a circular hole and subjected to uniaxial tension were analyzed.
Abstract: Experimental and finite-element analyses are presented for the anisotropic states of stress, strain and fracture of a glass-epoxy plate containing a circular hole and subjected to uniaxial tension. Strains were experimentally measured using foil gages, moire and birefringent coating. Stresses are computed in the linear range from the measured strains. While the hole reduces the plate strength by a factor of two, the maximum tensile strain at fracture is greater than the ultimate strain in a plate without a hole. Fracture consists of crack initiation at the hole boundary but off the horizontal axis. Away from the hole, failure is accompanied by considerable delamination. Discontinuous crack propagation is present.

47 citations


Journal ArticleDOI
TL;DR: In this article, a universal test machine applied the axial tensile or compressive stress; an independent pressurization system supplied the internal pressure to the specimen, and changes in diameter, length and wall thickness were measured at room temperature and at −50°F.
Abstract: Thin-walled tubes of rigid polyurethane foam, at 5 lb/cu ft and 4 lb/cu ft nominal density, were subjected to combined stresses. A universal-test machine applied the axial tensile or compressive stress; an independent pressurization system supplied the internal pressure to the specimen. Changes in diameter, length and wall thickness were measured at room temperature and at −50°F. Failure envelopes in 2-dimensional stress space were obtained for the two densities at room temperature and for the greater density at −50°F. For the wall-thickness range investigated (0.15≤t≤0.25 in.), no effect on the failure envelope was observed. Material constants were obtained in terms of orthotropic elastic theory (at 5 lb/cu ft and room temperature) to describe the material in terms of structure.

44 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the stress singularity created by a concentrated load applied at the boundary of a half-plane by transforming it into an optical singularity by the optical method of caustics.
Abstract: The stress singularity created by a concentrated load applied at the boundary of a half-plane was studied by transforming it into an optical singularity by the optical method of caustics. The half-plane was considered to be elastic, isotropic and under generalized plane-stress conditions. According to the method of caustics, the light rays impinging normally at the thin plate are partly reflected from either the front or the rear faces of the plate. The reflected rays are deviated because of the important constraint of the plate at the vicinity of the applied load and the significant variation of the refractive index there. The deviated light rays, when projected on a reference screen, are concentrated along a singular curve which is, therefore, strongly illuminated and forms a caustic. It is shown that the shape and size of the caustic depends on the stress singularity at the point of application of the load. Thus, by measuring the dimensions of this singular curve, one can evaluate the state of stress at the singularity. The characteristic properties of the caustic created by such a singularity were studied in relation with the loading mode of the plate.

43 citations


Journal ArticleDOI
TL;DR: In this paper, a method for estimating the Mode I stress-intensity factor using holographic interferometry and test pieces cut from thin sheets of commercially available polymethylmethacrylate is described and demonstrated.
Abstract: The use of linear elastic fracture mechanics generally depends upon the availability of suitable analytical or numerical solutions for the relevant crack-tip stress-intensity factor,K. Convenient experimental verification of such solutions is a valuable aid to their correct application and can provide a practical substitute in real design situations of great complexity. A convenient, new experimental technique for estimating the Mode I stress-intensity factor using holographic interferometry and test pieces cut from thin sheets of commercially available polymethylmethacrylate is described and demonstrated. The test pieces can readily be prepared to model any desired Mode I geometry and boundary conditions. In addition, a prior self-calibration procedure can be employed to enhance both convenience and accuracy. Real-time interference-fringe data from the crack-tip region are easily reduced and plotted to yield a straight line whose slope provides a one-parameter evaluation of the effect of geometry on the stress-intensity factor. This information, together with the crack length and applied stress, completely definesK.

42 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of out-of-phase or nonsychronous straining on low-cycle fatigue was investigated, and an analysis based on the maximum total strain in three-dimensional strain was proposed for treating 'out-ofphase' straining conditions in low-cycled fatigue.
Abstract: The effects of out-of-phase or nonsychronous straining on low-cycle fatigue was investigated. Biaxial strains were imposed on thin-walled tubular 7075-T6 aluminum specimens by tension-compression and torsion. Phase angles of 0, 30, 45, 60, and 90 deg were applied between two strains. It was found that out-of-phase cycling has an effect on the failure mode in the low-cycle-fatigue range. An analysis based on the maximum total strain in three-dimensional strain is proposed for treating 'out-of-phase' straining conditions in low-cycle fatigue.

38 citations


Journal ArticleDOI
C. W. Smith1
TL;DR: In this paper, the Taylor series correction for the maximum in-plane shear stress (TSCM) was used to determine the stress intensity factor photoelastically for three-dimensional problems.
Abstract: The philosophy of fracture mechanics is reviewed and utilized to formulate a simplified approach to the determination of the stress-intensity factor photoelastically for three-dimensional problems. The method involves a Taylor Series correction for the maximum in-plane shear stress (TSCM) and does not involve stress separation. The results are illustrated by applying the TSCM to surface flaws in bending fields. Other three-dimensional problems solved by the TSCM are cited.

Journal ArticleDOI
TL;DR: The smoothed spline as discussed by the authors is a method for obtaining high quality derivatives in experimental-mechanics problems, and methods for controlling the amount of smoothing and for avoiding derivative approximation deficiencies at the spline boundaries are presented.
Abstract: The smoothed spline is presented as a method for obtaining high-quality derivatives in experimental-mechanics problems. The smoothed spline is discussed and methods for controlling the amount of smoothing and for avoiding derivative approximation deficiencies at the spline boundaries are presented. Applications are examined for scattered-light photoelasticity and the bending of beams.

Journal ArticleDOI
TL;DR: In this article, 20 tests were performed on a 1 Cr−1 Mo−1/4 V rotor steel at 1000° F (538°C) to determine the interaction of creep and low-cycle fatigue.
Abstract: Twenty tests were performed on a 1 Cr−1 Mo−1/4 V rotor steel at 1000° F (538°C) to determine the interaction of creep and low-cycle fatigue. These tests involved five different types of strain-controlled cycling: creep at constant tensile stress; linearly varying strain at different frequencies; and hold periods at maximum compressive strain, maximum tensile strain, or both.

Journal ArticleDOI
TL;DR: In this paper, the authors determined the viscoelastic response of intact human cornea subjected to physiological intraocular pressure from local deformations measured by a flying spot micrometer.
Abstract: Viscoelastic response of intact human cornea subjected to physiological intraocular pressure was determined from local deformations measured by a flying spot micrometer. One eye of a paired specimen was prepressurized at 15 mmHg for at least 8 hr while the other eye was left unpressurized before testing. Test results of five paired eyes showed that, in prepressurized enucleated eyes, the viscoelastic response was insignificant while significant viscoelastic response existed in the nonpressurized eyes. The latter viscoelastic properties were characterized by a five-element linear viscoelastic model and a nonlinear hereditary integral by Fung.

Journal ArticleDOI
TL;DR: In this article, it was shown that without having found the correct angle γ, the values of stresses obtained were such that emax was less than emin for some strain relaxations.
Abstract: It is known that the hole-drilling technique to determine the surface residual stresses is a very useful tool. It has been shown in this work that without having found the correct angle γ, the values of stresses obtained were such that emax was less than emin for some strain relaxations. This point was not considered in the previous work. The present work points out this anomaly, gives a set of equations for a rosette of general configuration, reduces these equations for a rectangular rosette and gives a method to yield correct principal stresses and their directions. It is thus concluded here that the determination of the correct angle γ is very necessary to evaluate the stresses correctly; without doing so, the results are suspect and, thus, are of no use. It must be mentioned here that the method of determining the correct angle as described in this article is useful not only in the hole-drilling technique but also in any analysis where the angle is to be computed by taking the inverse of a trigonometric function. This method has been used by the author in the determination of the directions of the resultant bearing loads in a crankshaft.

Journal ArticleDOI
TL;DR: Moire techniques were developed, adapted and applied to the determination of strain fields in filamentary composite laminates as mentioned in this paper, using 1000 line-per-inch (Ipi) arrays bonded or photoprinted onto the specimen, were applied to glass-epoxy and boron-poxy specimens with holes and cracks.
Abstract: Moire techniques were developed, adapted and applied to the determination of strain fields in filamentary composite laminates. Conventional techniques, using 1000 line-per-inch (Ipi) arrays bonded or photoprinted onto the specimen, were applied to glass-epoxy and boron-epoxy specimens with holes and cracks. Techniques for tenfold fringe multiplication were also applied to glass-epoxy and boron-epoxy laminates with holes. A reflective surface of glass-like smoothness was produced on the specimen and a 500 dot-per-inch grid photoprinted on it. A rigid distortion-free camera was used for recording replicas of the specimen grid by projection photography. These replicas were analyzed with a 200 line-per-millimeter (5080 Ipi) grating for reconstruction of moire-fringe patterns. These patterns were analyzed by graphical and mechanical differentiation using second-order moire. Strain distributions and strain-concentration factors were in very good agreement with theoretical and other experimental results.

Journal ArticleDOI
N. Yamaki1, K. Otomo1
TL;DR: In this article, the postbuckling behavior of circular cylindrical shells under hydrostatic pressure was investigated by using lap-jointed polyester test cylinders with radius 100 mm, thickness 0.25 mm and lengths ranging from 23 to 165 mm.
Abstract: Detailed experimental studies are performed on the postbuckling behavior of circular cylindrical shells under hydrostatic pressure, by using lap-jointed polyester test cylinders with radius 100 mm, thickness 0.25 mm and lengths ranging from 23 to 165 mm. Connections of the edge shortening and radial displacement with applied pressures as well as wave forms for typical postbuckling configurations are determined for various values of the shell curvature parameterZ ranging from 20 to 1000. It is found that the buckling pressure and the corresponding wave number for each cylinder compare favorably with those theoretically predicted, and that the minimum pressure after buckling decreases with the increase inZ, until it becomes about 70 percent of the theoretical buckling pressure for long shells withZ greater than 200.

Journal ArticleDOI
TL;DR: In this article, the least squares method is presented for obtaining an overdetermined solution from the various relationships available in photoelastic stress analysis, and the results are illustrated in two example problems.
Abstract: The least-squares method is presented for obtaining an overdetermined solution from the various relationships available in photoelastic stress analysis. Equations are presented for incorporating the various relations into a weighted least-squares solution and advantages of this method are illustrated in two example problems. In addition to the greater accuracy possible in the overdetermined solution, the method permits weighting of the varied information and eliminates the need to separately determine the stress-optical constant. Variations of the method are discussed.

Journal ArticleDOI
TL;DR: In this article, an analytical and experimental investigation was performed to determine the natural frequencies and mode shapes of a cone-cylinder segmented shell, and the results were in good agreement with one another.
Abstract: An analytical and experimental investigation was performed to determine the natural frequencies and mode shapes of a cone-cylinder segmented shell. The finite-element technique was used to predict the natural frequencies and mode shapes of a clamped segmented shell. In the experimental phase of the program, the shell was excited by an electromagnet and the natural frequencies were determined with the aid of a microphone. Holographic interferometry was used to identify the mode shapes for each resonant frequency. The analytical and experimental results were in good agreement with one another.

Journal ArticleDOI
TL;DR: In this article, the authors used cubic-spline and discrete-quadratic polynomial techniques for reliably computing up to third-order derivatives of experimental information and demonstrated the concept by stress analysis from measured displacements a transversely loaded plate and a beam under four-point bending.
Abstract: Cubic-spline and discrete-quadratic polynomial techniques are presented for reliably computing up to third-order derivatives of experimental information. The concept is demonstrated by stress analyzing from measured displacements a transversely loaded plate and a beam under four-point bending. The respective displacement fields were recorded using holography and moire. The accuracy of the employed numerical-differentiation techniques is indicated.

Journal ArticleDOI
TL;DR: In this article, two approaches are proposed to extend the Ligtenberg reflective moire method to dynamic bending problems of plates, and partial slope contours of two orthogonal directions can be obtained simultaneously with the proposed schemes.
Abstract: Two approaches are proposed to extend the Ligtenberg’s reflective moire method to dynamic-bending problems of plates. Partial slope contours of two orthogonal directions can be obtained simultaneously with the proposed schemes. Vibrating modes of plates can also be obtained by the methods.

Journal ArticleDOI
TL;DR: The application of time-averaged holography to the analysis of vibrating surfaces is now a widespread and very powerful experimental technique as discussed by the authors, and the real-time method of exactly superimposing the reconstructed static image on the vibrating object and observing the resulting fringe patterns under stroboscopic illumination is becoming more common.
Abstract: The application of time-averaged holography to the analysis of vibrating surfaces is now a widespread and very powerful experimental technique. However, the realtime method of exactly superimposing the reconstructed static image on the vibrating object and observing the resulting fringe patterns under stroboscopic illumination is becoming more common. In fact, by introducing an initial family of interference fringes by the rotation of the object (or image) before vibration begins, the advantages of both methods are combined.

Journal ArticleDOI
TL;DR: In this paper, the problem of longitudinal impact of a thin finite-joined shell, consisting of a cylinder-truncated cone-cylinder, is analyzed both experimentally and analytically.
Abstract: The problem of longitudinal impact of a thin finite-joined shell, consisting of a cylinder-truncated cone-cylinder, is analyzed both experimentally and analytically. the model analyzed is a 1/100-scale replica of a portion of the Apollo/Saturn V vehicle. Experimental results were obtained from a drop-test system. Longitudinal and circumferential strain pulses were monitored on each section of the joined shell. The velocity of the impacter ring prior to impact was measured and used as a boundary condition in the solution of the governing partial-differential equations. A “bending” theory, including transverse-shear, radial-inertia and rotary-inertia effects, was used to analyze the finite-joined shell. Appropriate transformation relations were developed at each of the joints between the cylinders and truncated cone. The results were then obtained by solving the governing equations numerically by the method of characteristics. Good agreement between analytical and experimental strain profiles was obtained.

Journal ArticleDOI
Shuji Taira1
TL;DR: The X-ray diffraction is one of the most powerful means for investigating the microscopic structure of crystalline materials as discussed by the authors, and it has been applied to metallic materials; it responds very sensitively to changes in the metal's crystalline structure.
Abstract: It is well known that X-ray diffraction is one of the most powerful means for investigating the microscopic structure of crystalline materials. X-ray diffraction is advantageous when it is applied to metallic materials; it responds very sensitively to changes in the metal's crystalline structure. Another characteristic advantage of the X-ray-diffraction approach is its nondestructive nature in the measurement of crystalline-material parameters, enabling us to observe the process of mechanical phenomena of metals, such as fatigue and creep.

Journal ArticleDOI
TL;DR: In this article, the out-of-plane deflection in a thin tensioned sheet containing a central opening is discussed, and it is noted that this behavior is of practical importance because it can alter the stress concentration and fatigue properties.
Abstract: The out-of-plane deflection which can be developed in a thin tensioned sheet containing a central opening is discussed. It is noted that this behavior is of practical importance because it can alter the stress concentration and fatigue properties.

Journal ArticleDOI
TL;DR: In this article, the authors focus initially on the recognition of fracture problems and the experimental investigations that developed in response to them, including fracture propagation studies in plates and pipelines, and fracture propagation in pipelines.
Abstract: The treatment of this topic is selective; it concentrates initially on the recognition of fracture problems and the experimental investigations that developed in response to them, including fracture-propagation studies in plates and pipelines.

Journal ArticleDOI
TL;DR: In this paper, a technique for the study of acoustic emission during high-cycle-fatigue crack propagation has been developed, and data from a fatigue test are presented demonstrating accoustic-emission behavior for crack-growth rates from 3×10−6 in./cycle to 70×10 −6 in/cycle.
Abstract: A technique for the study of acoustic emission during high-cycle-fatigue crack propagation has been developed. Difficulties resulting from complex emission behavior and the low signal-to-noise ratio encountered in this type of test are rectified by three methods: minimization of mechanical noise; separation of noise causes according to position in the loading cycle; and rejection of noise from sources other than the crack by a short-time correlation method. The approaches are discussed and data from a fatigue test are presented demonstrating accoustic-emission behavior for crack-growth rates from 3×10−6 in./cycle to 70×10−6 in./cycle.

Journal ArticleDOI
Walter Schumann1
TL;DR: In this article, a comparison of different optical methods where either photoelastic models, opaque bodies with transparent coatings or noncontacted objects are examined with coherent light is made, and some common features are contained by the three groups.
Abstract: In a general view, a comparison is made of different optical methods where either photoelastic models, opaque bodies with transparent coatings or noncontacted objects are examined with coherent light. Further, it is tried to show that some common features are contained by the three groups. These aspects concern the separation, by controlled determination, of displacement, rotation and strain (or of certain of their components), the multiplication of the optical effects in the detection and the elimination of secondary influences. In particular, the noncontacting method of wavefront reconstruction with double-exposure holograms is discussed and the role of the localization condition for the fringes in space is analyzed. On the other hand, it is illustrated that, besides the generally known birefringence and diffraction. use could be made of nonorthodox effects like rotation of the plane of polarization, second-harmonic generation in nonlinear optics, etc. This may, for instance, contribute to the optical instrumentation when transparent models and bodies with photoelastic coatings are investigated under the above aspects.

Journal ArticleDOI
TL;DR: In this paper, the effect of end fixity on the strength of composite cylindrical characterization specimens subjected to axisymmetric loading is studied both analytically and experimentally Flugge's shell theory in conjunction with the maximum-strain criterion.
Abstract: The effect of end fixity on the strength of composite cylindrical characterization specimens subjected to axisymmetric loading is studied both analytically and experimentally Flugge's shell theory in conjunction with the maximum-strain criterion is used to study the effect of end moments and load introduction on tube strength Analytical results are compared to data obtained on graphite/epoxy fiber-reinforced tubes and flat specimens

Journal ArticleDOI
TL;DR: In this paper, the components of displacement in the axial direction throughout the surface of a unilayer, fiber-reinforced-composite tension specimen subjected to low-speed loading are established experimentally.
Abstract: In this investigation, the components of displacement in the axial direction throughout the surface of a unilayer, fiber-reinforced-composite tension specimen subjected to low-speed loading are established experimentally. The experimental results are used to evaluate the strain distribution throughout the surface of the specimen; to establish the strain concentration at the surface in the neighborhood of broken fibers; and to evaluate other factors.