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Showing papers in "Experimental Mechanics in 1998"


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a technique that compares digital images of a specimen surface before and after deformation to deduce its two-dimensional surface displacement field and strain components.
Abstract: This is the second paper in a series of three devoted to the application of scanning tunneling microscopy (STM) 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 two-dimensional 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 STM data; also, significant improvements are achieved in the rate as well as the robustness of the convergence. For (STM) topographs, the resolution yields 4.8 nm for the in-plane and 1.5 nm for the out-of-plane displacement components spanning an area of 10 μm×10μm.

524 citations


Journal ArticleDOI
C. Bacon1
TL;DR: In this paper, an experimental method was developed to perform Hopkinson tests by means of viscoelastic bars by considering the wave propagation attenuation and dispersion due to the material rheological properties and the bar radial inertia (geometric effect).
Abstract: An experimental method is developed to perform Hopkinson tests by means of viscoelastic bars by considering the wave propagation attenuation and dispersion due to the material rheological properties and the bar radial inertia (geometric effect). A propagation coefficient, representative of the wave dispersion and attenuation, is evaluated experimentally. Thus, the Pochhammer and Chree frequency equation is not necessary. Any bar cross-section shapes can be employed, and the knowledge of the bar mechanical properties is useless. The propagation coefficients for two PMMA bars with different diameters and for an elastic aluminum alloy bar are evaluated. These coefficients are used to determine the normal forces at the free end of a bar and at the ends of two bars held in contact. As an application, the mechanical impedance of an accelerometer is evaluated.

170 citations


Journal ArticleDOI
Bongtae Han1
TL;DR: In this article, the authors reviewed the applicability of both microscopic moire interferometry and whole field displacement information for the deformation study of a broad range of problems in deformation analyses of microelectronics devices.
Abstract: Moire and microscopic moire interferometry are reviewed as they are applied to thermal deformation analyses of microelectronics devices. Applications to diverse problems are illustrated to demonstrate wide applicability of the methods. The whole-field displacement information, with various sensitivity and resolution scales, is ideally suited for the deformation study of a broad range of problems in deformation analyses of microelectronics devices.

90 citations


Journal ArticleDOI
TL;DR: In this article, the effect of strain rate on the compressive behavior of thick carbon/epoxy composite materials was investigated, and the results showed that the 0-deg and cross-ply laminates showed higher strength and ultimte strain values as the strain rate increases, whereas the modulus increnases only slightly over the static value.
Abstract: The effect of strain rate on the compressive behavior of thick carbon/epoxy composite materials was investigated. Falling weight impact and split Hopkinson pressure bar systems were developed for dynamic characterization of composite materials in compression at strain rates up to 2000 s−1. Strain rates below 10 s−1 were generated using a servohydraulic testing machine. Strain rates between 10 s−1 and 500 s−1 were generated using the drop tower apparatus. Strain rates above 500 s−1 were generated using the split Hopkinson pressure bar. Unidirectional carbon/epoxy laminates (IM6G/3501-6) loaded in the longitudinal and transverse directions, and\([(0_8 /90_8 )_2 /\bar 0_8 ]_s \) cross-ply laminates were characterized. The 90-deg properties, which are governed by the matrix, show an increase in modulus and strength over the static values but no significant change in ultimate strain. The 0-deg and cross-ply laminates show higher strength and ultimte strain values as the strain rate increases, whereas the modulus increnases only slightly over the static value. The increase in strength and ultimate strain observed may be related to the shear behavior of the composite and the change in failure modes. In all cases, the dynamic stress-strain curves stiffen as the strain rate increases. The stiffening is lowest in the longitudinal direction and highest in the transverse direction.

72 citations


Journal ArticleDOI
TL;DR: In this article, an all-polymeric split Hopkinson bar (APSHB) experiment was proposed for measuring high strain rate properties of high-strength materials, such as polycarbonate, polyurethane foam and styrofoam.
Abstract: The split Hopkinson bar is a reliable experimental technique for measuring high strain rate properties of high-strength materials. Attempts to apply the split Hopkinson bar in measurement on more compliant materials, such as plastics, rubbers and foams, suffer from limitations on the maximum achievable strain and from high noise-to-signal ratios. The present work introduces and all-polymeric split Hopkinson bar (APSHB) experiment, which overcomes these limitations. The proposed method uses polymeric pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials, thus providing both a low noise-to-signal ratio data and a longer input pulse for higher maximum strain. The APSHB requires very careful data reduction procedures because of the viscoelastic behavior of the incident and transmitter pressure bars. High-quality stress-strain data for a variety of compliant materials, such as polycarbonate, polyurethane foam and styrofoam, are presented.

72 citations


Journal ArticleDOI
TL;DR: In this article, the deformation fields around a propagating crack tip from photographic films recorded by a high-speed Cranz-Schardin camera were used to compute the dynamic stress intensity factor and the remote stress component.
Abstract: Digital image processing was used to obtain the deformation fields around a propagating crack tip from photographic films recorded by a high-speed Cranz-Schardin camera. The in-plane displacements and strains determined from the process were then used to compute the dynamic stress intensity factor and the remote stress component parallel to the crack face.K dominance is discussed using the experimental data. Surface roughness of the fractured surface is also examined.

69 citations


Journal ArticleDOI
TL;DR: In this article, a special digital scanning tunneling microscope (STM) was designed to be coupled to a mechanically deforming specimen to study deformations of micromechanical material systems at the submicron scale.
Abstract: A new experimental method has been developed for studying deformations of micromechanical material systems at the submicron scale. To that end, a special digital scanning tunneling microscope (STM) was designed to be coupled to a mechanically deforming specimen. Operating in constant current mode, this digitally controlled STM records detailed topographies of specimen surfaces with a resolution of 10 nm in-plane and 7 nm out-of-plane over a 10 μ × 10 μ area. Three-dimensional displacement field information is extracted by comparing topographies of the same specimen area before and after deformation by way of a modified digital image correlation algorithm. The resolution of this (combined) displacement measuring method was assessed on translation and uniaxial tensile tests to be 5 nm for in-plane displacement components and 1.5 nm for out-of-plane motion over the same area. This is the first paper in a series of three in which the authors delineate the main features of this specially designed microscope and describe how it is constituted, calibrated and used with the improved version of the digital image correlation method to determine deformations in a test specimen at the nanoscale.

66 citations


Journal ArticleDOI
TL;DR: In this article, the authors revisited the application of thermocouples to such measurements using small embedded thermocouple (ETC) and showed that small ETCs can be embedded to yield useful information about the transient temperature evolution in a solid.
Abstract: The response time of thermocouples is generally considered to be a limiting factor when transient temperature changes need to be assessed in solids. As an example, transient temperature changes which develop during dynamic straining of materials, adiabatic shear band formation, dynamic fracture and related fields are often investigated using sophisticated noncontact measurement techniques such as infrared detectors. In these phenomena, the time scale is of the order of the microsecond. In this paper, the authors revisit the application of thermocouples to such measurements using small embedded thermocouples (ETC). Experiments with dynamically loaded polymeric disks (characteristic strain rate of 103 s−1) show that the thermocouples record transient temperatures with a short typical rise time of 10 μs as a result of the conversion of plastic deformation into heat. This observation is corroborated by the solution of the temperature distribution in a sphere subject to constant surface temperature which predicts the same fast reaction. Specifically, considering a sphere which is representative of the sensing bead, the average temperature is shown to rise in a few microseconds. These theoretical results can be used to deconvolve the experimental results with respect to a calculated impulse response of the sensor to recover the actual temperature variations. The results show that small thermocouples can be embedded to yield useful information about the transient temperature evolution in a solid. This technique is easy to use and provides an important complement to other noncontact techniques.

59 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental investigation of deformation mechanisms at the sub-micron scale through the use of a specially designed scanning tunneling microscope is presented, when used jointly with digital image correlation, as a tool for strain and deformation determinations.
Abstract: This is the third and last paper is a sequence devoted to an experimental investigation of deformation mechanisms at the submicron scale through the use of a specially designed scanning tunneling microscope. Its application, when used jointly with digital image correlation, as a tool for strain and deformation determinations is explored by way of two demonstrations. First, deformations in a uniaxially stressed, unplasticized (poly)vinylchloride sample are analyzed to yield the three-dimensional surface displacement field over a 10 μm×10μm area. Homogeneous deformations occur at the micrometer and large size scales. However, at the 100-nm scale, inhomogeneous deformations embedded in a homogeneous deformation field appear. The second example addresses the deformation field in the vicinity of an interface between a carbon fiber and the surrounding matrix under shear stresses along the fiber. This loading leads to shearing a sheath from the carbon fiber that is about half a micron thick.

57 citations


Journal ArticleDOI
TL;DR: In this article, the authors report the design and construction of a new measurement apparatus, along with the result of its testing, which can be placed at the midspan of the circular tube specimen and is suitable for simultaneous experimental determinations of the tube curvature and ovalization.
Abstract: In this paper, the authors report the design and construction of a new measurement apparatus, along with the result of its testing. This apparatus can be placed at the midspan of the circular tube specimen and is suitable for simultaneous experimental determinations of the tube curvature and ovalization of the tube cross section. For testing the newly designed apparatus, the tube specimen of AISI 304 stainless steel was bent cyclically. It has been shown that the actual curvature and ovalization of the circular tube subjected to bending can be directly measured by the apparatus.

53 citations


Journal ArticleDOI
TL;DR: In this paper, a capacitance-based noncontact displacement sensor mounted in an XYZ frame was used to measure the forces applied to the membrane, as well as the motion of theXYZ frame during data acquisition.
Abstract: True membranes are no-compression structures which exhibit the unique response of wrinkling. Prediction of the associated wrinkle parameters is of practical importance. Accurate measurement of membrane wrinkling has heretofore not been presented in the literature; among other requirements, noncontact methods must be used. First, some background information on membrane wrinkling prediction and measurement is given. Then, an experimental apparatus is discussed within which a membrane was subject to planar loading. The measurement system consisted of a capacitance-based noncontact displacement sensor mounted in anXYZ frame. A computer controlled the forces applied to the membrane, as well as the motion of theXYZ frame during data acquisition. Results are presented and conclusions are drawn regarding the wrinkle parameters.

Journal ArticleDOI
TL;DR: In this paper, a fine-wire thermocouple is used to calculate the heat losses that occur during the test and these heat losses are then accounted for in the final energy balance to determine the fraction of plastic work converted to heat.
Abstract: The fraction of plastic work converted to heat is typically measured either by nearly isothermal experiments, in which the thermal energy is measured during a deformation experiment with a calorimeter, or by adiabatic experiments, in which the thermal energy is determined from the temperature rise, measured either during the test or immediately after the test by dropping the sample into a calorimeter. In the present work, the temperature is measured with a single fine-wire thermocouple. The restriction to adiabatic loadings is relaxed by using a hybrid method that combines the measurements with finite difference simulations to calculate the heat losses that occur during the test. These heat losses are then accounted for in the final energy balance to determine the fraction of plastic work converted to heat. The method is applied to annealed 302 stainless steel. The results show that the fraction of plastic work converted to heat is a decreasing function ranging from 0.7 to 0.4 over a tensile strain range of 0 to 0.15. An analysis of the restrictions to this method and of the potential errors is given.

Journal ArticleDOI
TL;DR: In this paper, the strain field in an epoxy plate loaded in tension through a steel pin is determined using electronic speckle pattern interferometry (ESPI) and the finite element method (FEM).
Abstract: The strain field in an epoxy plate loaded in tension through a steel pin is determined using electronic speckle pattern interferometry (ESPI) and the finite element method (FEM). In a dual-beam illumination speckle interferometer, the in-plane component of the displacement at the plate's surface is accurately measured using a four-step phase-shifting algorithm. Digital image processing algorithms have been developed for noise reduction and strain calculation directly in the computer from the phase map with a strain gage length of about 0.4 mm. A whole-field strain map is obtained, as well as distributions of strain concentration factor, in critical regions near the hole of the plate. FEM is used to perform a nonlinear contact analysis accounting for friction effects at the pin/hole interface. The agreement between experimental results and numerical predictions is good. In terms of speed, accuracy and ease of use, dual-beam ESPI appears to be a superior method of whole-field strain analysis.

Journal ArticleDOI
TL;DR: In this paper, the effect of using white light has been investigated both by experiment and by a simulation of a polariscope, and the simulation has been validated and used to explore the use of bandwidth filters to control the errors caused by white light.
Abstract: In automated photoelasticity, there are some advantages in using white light; however, the theory underlying many such systems, namely phase stepping, is based on monochromatic light The effect of using white light has been investigated both by experiment and by a simulation of a polariscope The simulation has been validated and used to explore the use of bandwidth filters to control the errors caused by using white light These errors were found to be dependent on the form of the spectrum of the light and to be large for high fringe orders

Journal ArticleDOI
TL;DR: In this paper, the coefficients of thermal expansion (CTEs) of composite materials using electrical resistance strain gages are derived, accounting for the effects of transverse sensitivity and possible misalignment of the gages.
Abstract: The measurement of the coefficients of thermal expansion (CTEs) of composite materials using electrical resistance strain gages is addressed. Analytical expressions for the CTEs of an orthotropic lamina are derived, accounting for the effects of transverse sensitivity and possible misalignment of the gages. Experiments are performed for the characterization of the thermal expansion behavior of a fiber-glass-reinforced epoxy unidirectional lamina using an invar specimen as reference material. Preliminary training cycles are performed for the determination of an optimal heating rate for the measurements, which ensures thermal equilibrium conditions. Three measurement cycles yield the principal CTEs of the lamina α1, α2 and α12 with repeatability within ±0.34×10−6, ±0.85×10−6 and ±2.8×10−6/°C, respectively. It is noted that inhomogeneity of the specimen and variation in thermomechanical properties of the gages can cause a noticeable spead in the measurements.

Journal ArticleDOI
TL;DR: In this article, a model for the mechanics of thin polymer web slitting was proposed, and the results of the experiments showed that the in-plane cutting forces were minimally affected by changes in rate or web tension.
Abstract: The quality of edges formed during cutting and slitting of thin polymer webs is important for many industrial applications. To control the edge quality of the separated material, it is necessary to understand cutting. A model is proposed, and the mechanics of cutting are described. Experiments were conducted on polyethylene terephthalate. Photoelastic micrographs were used for qualitative and quantitative observations of the two-dimensional stress distributions. The results of this analysis supported the model for cutting of thin polymer webs. An apparatus was constructed to instrument, monitor and control the web-slitting process. The slitting speed, tension in the web and angle of cut were varied during tests. This allowed a quantitative understanding of the cutting mechanisms to be established. The results of the experiments showed that the in-plane cutting forces were minimally affected by changes in rate or web tension. The angle of cut had a pronounced effect on the in-plane cutting forces and the stability of the cut. The results are a beginning of a mechanistic understanding of deformation taking place during slitting and cutting. The experimentation emphasized an instability in slitting. An understanding of this instability will allow quality web edges with minimal deformation and straight stable cuts to be achieved.

Journal ArticleDOI
TL;DR: In this article, a new approach to full-field automated photoelasticity is presented in which a circular polariscope is used to enable the isochromatic phase value (α) to be determined unambiguously and without input of a known isochrome value obtained using an auxiliary technique.
Abstract: A new approach to full-field automated photoelasticity is presented in which a circular polariscope is used to enable the isochromatic phase value (α) to be determined unambiguously and without input of a known isochromatic value obtained using an auxiliary technique. Values of cosα are obtained from light-field and dark-field images for three loads of small incremental steps. Using a relatively straight-forward procedure, ramped phase maps for α are produced which can be unwrapped using conventional techniques. The resulting distribution of α is then found absolutely using information provided by which δα is the incremental change in the isochromatic phase value between the load steps. The results obtained for disk-in-compression tests presented here in comparison with theoretical solutions demonstrate that the technique is both simple to use and very accurate. A similar approach may be adopted using three wavelengths instead of three load steps.

Journal ArticleDOI
TL;DR: In this paper, the dynamic response of foil strain gages was investigated in the ranges of up to approximately 300 kHz in frequency, 2000 μe in strain and 750 s−1 in strain rate.
Abstract: Dynamic response of foil strain gages is investigated in the ranges of up to approximately 300 kHz in frequency, 2000 μe in strain and 750 s−1 in strain rate. Impulsive input is applied to the gages using elastic wave pulses in a circular bar. The input is determined by measuring the velocity of the bar end with a laser interferometer. It was confirmed that deviations from the static gage factors do not exceed−5 percent within the frequency range up to 45 kHz, 110 kHz and more than 290 kHz for 20-mm, 10-mm and 3-mm gages, respectively, and that the gage length is the dominant factor in the gages' frequency characteristics. This paper also mentions self-generated voltages.

Journal ArticleDOI
TL;DR: The Alamillo Bridge as discussed by the authors is a cable-stayed structure spanning 200 m without any intermediate supports and its originality is the lack of back stays and the balancing of the front stays through the backward inclination of a massive pylon.
Abstract: The Alamillo Bridge is one of the long-span bridges crossing the Guadalquivir River. It was built on the occasion of Expo '92 in 1992 in Sevilla, Spain. The bridge is a cable-stayed structure spanning 200 m without any intermediate supports. Its originality is the lack of back stays and the balancing of the front stays through the backward inclination of a massive pylon. This paper shows the importance of experimental in situ techniques when applied to unconventional civil engineering structures and how—with the help of an important amount of accurate instrumentation, monitoring the most important experimental variables—it was possible to build the bridge correctly, safely, and on schedule.

Journal ArticleDOI
TL;DR: In this paper, the authors used experimental modal analysis to validate a hollow golf club head finite element model to predict the impact performance of real and simulated impacts on a golf ball.
Abstract: The design of modern hollow golf club heads is a labor-intensive process involving extensive performance festing both by robotic and real golfers. This paper describes how, by correlating club head mechanical behavior with functional performance, it will become possible to use validated computational models to predict this performance as well as related contributions to the ill-defined concept of “feel”. Successful use of experimental modal analysis to validate a hollow golf club head finite element model is reported. Modal tests employing noncontacting, laser-based transducers facilitated identification of the natural frequencies and corresponding modeshapes for the three main surfaces of the club head. The experimental data suggest predominantly different modal characteristics for each surface, and this compares favorably with equivalent data obtained from the finite element model. The modal data are also used to identify surfaces responsible for particular frequency components present in the club head impact sound spectrum. The potential for detailed impact performance prediction using the finite element model is further demonstrated by comparison of computed and experimental club head acceleration measurements recorded during simulated and actual club-ball impacts.

Journal ArticleDOI
TL;DR: In this paper, a modal testing method permitting identification of the natural frequencies, the number of nodal diameters and wave motions in a rotating disk is presented, which is applicable at arbitrary rotation speed without requiring a priori information about the vibration modes of the stationary disk.
Abstract: A modal testing method permitting identification of the natural frequencies, the number of nodal diameters and wave motions in a rotating disk is presented in this paper. This method is applicable at arbitrary rotation speed without requiring a priori information about the vibration modes of the stationary disk. The influence of disk rotation speed on the prediction of mode shapes with this method is shown, and experimental predictions of modal parameters are presented for both axisymmetric and asymmetric disks.

Journal ArticleDOI
TL;DR: In this paper, the authors modified the pressure-shear plate impact experiment to test materials at high temperatures (up to 700°C) to measure the shearing resistance of tungsten carbide materials under conditions unattainable with other testing equipment.
Abstract: The pressure-shear plate impact experiment has been modified to test materials at high temperatures (up to 700°C). Together with the high strain rates characteristic of this experiment (106 s−1), the high-temperature capability allows the shearing resistance of materials to be measured under conditions unattainable with other testing equipment. The compressive and shear responses of pure tungsten carbide at different temperatures are presented, as well as the results of one test on OFHC copper at a temperature of 691°C and a shear strain rate of 1.4×106 s−1.

Journal ArticleDOI
TL;DR: In this article, the authors study erros incurred when using the experimental technique of electron-beam moire and demonstrate the usefulness of the error estimate by investigating the thermal expansion of commercially pure copper, with a possible error due to apparent magnification drift of 9 percent.
Abstract: In this paper, the authors study erros incurred when using the experimental technique of electron-beam moire. There are two sources of error: error manifested as an apparent magnificant drift and error due to fringe tracing. The error due to fringe tracing is nearly negligible in comparison to the error due to magnification drift. By investigating the thermal expansion of commercially pure copper, the authors demonstrate the usefulness of the error estimate. The average result for the coefficient of thermal expansion is within 1.8 percent of handbook values for this materials, with a possible error due to apparent magnification drift of 9 percent.

Journal ArticleDOI
TL;DR: In this paper, the authors performed impact experiments on edgenotched specimens in the two-dimensional punch geometry and found that shear bands formed at the notch tip and at the die corner on the back side of the specimen for all materials tested.
Abstract: Impact experiments are performed on edgenotched specimens in the two-dimensional punch geometry. Materials tested include 18Ni(350) maraging steel; S7 tool steel; 4340, 300M, HP 9-4-20 and D-6ac ultra high-strength steels; and Ti6Al4V alloy. These materials have shown a high susceptibility to dynamic shear failure in previous studies. Impact velocity ranged from 25 m/s to 45 m/s, and shear bands were found to form at the notch tip and at the die corner on the back side of the specimen for all materials tested. Metallurgical analysis confirms the existence of adiabatic shear bands followed by a crack propagating through the fully developed shear band. High-speed photography was used to observe the initiation of adiabatic shear bands shortly after impact. Laser-etched lines on the specimen surfaces allowed the determination of the time of impact and the initiation time of shear failure. The elapsed time between the two was used to estimate the stress intensity factor at the time of shear band initiation. Comparisons of shear band initiation stress intensity factors at the notch tip and die corner are made. It is seen that the shear bands initiate at approximately the same stress intensity factor at both the notch tip and die corner. Finite element simulations support the use of a square root singularity for the stress in the plate near the corners of a deformable punch or die.

Journal ArticleDOI
TL;DR: In this article, the authors used and developed a series of methods and test pieces to evaluate the reliability and accuracy of the gear model assemblies and compared the results with appropriate experimental results.
Abstract: Gears of different sizes and with different systems of loading are indispensable components of machines and devices. When optimizing such gear assemblies, on of the most important parameters is their required service life. To calculate the service life as precisely and reliably as possible, researchers need to use the required mathematical models for describing loading, the geometry, properties of materials and fracture mechanics parameters. The accuracy and reliability of the gear model assemblies can be compared only with appropriate experimental results. To this end, the authors have used and developed a series of methods and test pieces. A comparison of results has shown that the models and approaches are adequate.

Journal ArticleDOI
TL;DR: In this article, an experimental technique is presented for measuring the heat dissipation and localization during cyclic loading of materials, where the temperature field is measured by a number of thermistors and an infrared camera, which scans the specimen surface continuously.
Abstract: An experimental technique is presented for measuring the heat dissipation and localization during cyclic loading of materials. The temperature field is measured by a number of thermistors and an infrared camera, which scans the specimen surface continuously. The specimen is mounted inside an isothermal chamber. The measured whole-field temperature can be used for detection of damage propagation and localization. The resolution of the technique under various boundary conditions is discussed using a onedimensional model for the heat loss under steady-state conditions. Applications of the technique are demonstrated for specimens made of fiber-reinforced ceramic and polymer matrix composites (PMCs). A methodology is proposed for measuring changes in damping and stiffness properties of viscoelastic polymer matrix composites using the temperature rise of a cyclic loaded specimen. It is demonstrated that for a ceramic matrix composite, where interfacial frictional sliding gives rise to heat dissipation, the temperature resolution can be used for detection of stress-strain hysteresis with an accuracy better than that of the stress-strain data.

Journal ArticleDOI
TL;DR: In this article, the same instrument is used in a different way to measure change in the ultrasonic measurements due to bending in the bolts, resulting in a rotation and a translation of ultrasonic pulse reflecting face.
Abstract: An ultrasonic pulse/echo technique is used to measure preload in bolts used in structural joints. In this paper, the same instrument is used in a different way to measure change in the ultrasonic measurements due to bending in the bolts. A theory that explains the ultrasonic measurements is developed. The bending loads result in a rotation and a translation of the ultrasonic pulse reflecting face. It also creates a stress gradient in the bolt. This results in a phase variation (or gradient) in the received ultrasonic beam across the face of the transducer. It also results in a physical shift in the received beam relative to the ultrasonic transducer. The phase gradient and the shift in the beam results in change in the pulse travel time. A number of experiments were performed on the bolt to study the effect of the bending on the ultrasonic measurements. The experiments and the theory validate a sensitive new method for measuring the bending loads in the bolts.

Journal ArticleDOI
TL;DR: In this article, a method for simultaneous determination of both fringe order and principal direction of birefringence in practical photoviscoelastic analysis using white incident light with a set of the primary colors, called tricolor photoviscelasticity, is described.
Abstract: A new technique for simultaneous determination of both fringe order and principal direction of birefringence in practical photoviscoelastic analysis using white incident light with a set of the primary colors, called tricolor photoviscoelasticity, is described. This method can determine both the fringe order and principal direction of birefringence from a single-color photoviscoelastic image under plane polarization. Then, the authors evaluate time dependent stresses and strains around a contact region in a viscoelastic strip plate under nonproportional loading condition. The variations of the principal stresses and strains are easily obtained over a wide time range by use of the optical constitutive equations of photoviscoelasticity and the characteristic material property functions.

Journal ArticleDOI
TL;DR: In this paper, a parametric investigation is conducted to study the influence of various parameters such as the crack-tip velocity and the contact coefficient on the isochromatic fringe patterns.
Abstract: The isochromatic fringe patterns surrounding an intersonically propagating interface crack are developed and characterized using the recently developed stress field equations. A parametric investigation is conducted to study the influence of various parameters such as the crack-tip velocity and the contact coefficient on the isochromatic fringe patterns. It has been observed that the crack-tip velocity has a significant effect on the size and shape of isochromatic fringe patterns. The contact coefficient, on the other hand, does not affect the fringe pattern significantly. The paper also presents a numerical scheme to extract various parameters of interest such as the series coefficients of the stress field, the contact coefficient and the dissipation energy. The results show that the crack growth is highly unstable in the intersonic regime, and the energy dissipation decreases monotonically with increasing crack-tip velocity. The experimental data fit well with the recently proposed fracture criterion for intersonic interfacial fracture.

Journal ArticleDOI
TL;DR: An image-processing-based measurement system by which an automatic large deformation characterization and interactive force control can be realized, provided by a servo-controlled CCD camera and a PC-based frame grabber is described.
Abstract: This paper describes an image-processing-based measurement system by which an automatic large deformation characterization and interactive force control can be realized. The system is provided by a servo-controlled CCD camera and a PC-based frame grabber. A tracking procedure based on the location of a target point is employed for guiding the camera movement. It is intended to monitor the local deformation in a relatively small moving area containing small globules. The globule positions are then used to determine the surface deformation characteristics. In this system, the momentary principal strains being computed online are immediately used to control the applied force. As an illustration, the present system is applied for observing a long-term homogeneous large deformation in SI-rubber specimens being subjected to a constant uniaxial true stress. Four solid, minuscule, relatively undeformable polystyrene globules are used as markers. A true stress control algorithm is developed based on the isotropy assumption in which the transverse area normal to the loading direction becomes determinable from the surface deformation data. It can be stated that the maximum speed of the true stress control is mainly related to the speed of image processing and analysis, which in turn is related to the chosen number of globules and the performance of the PC used. By using four globules, the true stress readjustment could be accomplished for roughly every 4 s. For a large-strain deformation of SI-rubber, it appears that the isotropy assumption is acceptable, since the resulting mean difference between out-of-plane contraction and in-plane contraction is restricted to about±8 percent.