Showing papers in "Experimental Mechanics in 2000"
TL;DR: In this paper, a second-order approximation of the displacement gradients is proposed to directly measure both the first-and secondorder displacement gradient resulting from nonlinear deformation, which can be used to obtain more accurate strain measurements in large deformation situations.
Abstract: This paper outlines the procedure for refining the digital image correlation (DIC) method by implementing a second-order approximation of the displacement gradients. The second-order approximation allows the DIC method to directly measure both the first- and second-order displacement gradients resulting from nonlinear deformation. Thirteen unknown parameters, consisting of the components of displacement, the first- and second-order displacement gradients and the gray-scale value offset, are determined through optimization of a correlation coefficient. The previous DIC method assumes that the local deformation in a subset of pixels is represented by a first-order Taylor series approximation for the displacement gradient terms, so actual deformations consisting of higher order displacement gradients tend to distort the infinitesimal strain measurements. By refining the method to measure both the first- and second-order displacement gradients, more accurate strain measurements can be achieved in large-deformation situations where second-order deformations are also present. In most cases, the new refinements allow the DIC method to maintain an accuracy of ±0.0002 for the first-order displacement gradients and to reach ±0.0002 per pixel for the second-order displacement gradients.
370 citations
TL;DR: In this paper, a servohydraulic load frame was used to measure mechanical properties at lower strain rates, 10−3 s−1 to 1 s− 1, and a Kolsky pressure bar was used for higher strain rates.
Abstract: This study investigates heat generation in metals during plastic deformation. Experiments were designed to measure the partition of plastic work into heat and stored energy during dynamic deformations under adiabatic conditions. A servohydraulic load frame was used to measure mechanical properties at lower strain rates, 10−3 s−1 to 1 s−1. A Kolsky pressure bar was used to determine mechanical properties at strain rates between 103 s−1 and 104 s−1. For dynamic loading, in situ temperature changes were measured using a high-speed HgCdTe photoconductive detector. An aluminum 2024-T3 alloy and α-titanium were used to determine the dependence of the fraction of plastic work converted to heat on strain and strain rate. The flow stress and β for 2024-T3 aluminum alloy were found to be a function of strain but not strain rate, whereas they were found to be strongly dependent on strain rate for α-titanium.
310 citations
TL;DR: In this paper, a piezoelectric force transducer was embedded in the middle of the transmission bar of a high-strength aluminum alloy to directly measure the weakly transmitted force profile from a soft specimen and a pulse shape technique was used for increasing the rise time of the incident pulse to ensure stress equilibrium and homogeneous deformation in the low-impedance and low-strength specimen.
Abstract: A dynamic experimental technique that is three orders of magnitude as sensitive in stress measurement as a conventional split Hopkinson pressure bar (SHPB) has been developed. Experimental results show that this new method is effective and reliable for determining the dynamic compressive stress-strain responses of materials with low mechanical impedance and low compressive strengths, such as elastomeric materials and foams at high strain rates. The technique is based on a conventional SHPB. Instead of a surface strain gage mounted on the transmission bar, a piezoelectric force transducer was embedded in the middle of the transmission bar of a high-strength aluminum alloy to directly measure the weakly transmitted force profile from a soft specimen. In addition, a pulse-shape technique was used for increasing the rise time of the incident pulse to ensure stress equilibrium and homogeneous deformation in the low-impedance and low-strength specimen.
156 citations
TL;DR: In this paper, an improved calibration method for infrared radiometers is developed that has been shown to increase the accuracy of temperature measurement, and the proportion of plastic work converted to heat, β, is found to increase with plastic strain for both materials.
Abstract: An improved calibration method for infrared radiometers is developed that has been shown to increase the accuracy of temperature measurement. To validate this new calibration technique, high strain rate compression tests are performed on the aluminum alloy BS 2011 and high strain rate torsion tests are performed on the titanium alloy 90% Ti-6%Al-4%V. The adiabatic temperature rise that occurs during these tests is measured using an infrared radiometer and validated, in the case of the compression tests, using fast response thermocouples. The proportion of plastic work converted to heat, β, is found to increase with plastic strain for both materials, which is similar to previous research. These results challenge the classical assumption that β has a constant value of approximately 0.95.
125 citations
TL;DR: In this article, a laser-based noncontacting strain sensor was used for tensile testing at temperatures up to 1200°C, which was adapted to a commercial tensile test machine equipped with an electrical furnace.
Abstract: This paper presents a newly developed laser-based noncontacting strain sensor suitable for temperatures up to 1200°C, which was adapted to a commercial tensile testing machine equipped with an electrical furnace. The principle of the strain sensor is based on tracking laser speckles through a digital correlation technique. Furthermore, the description of the signal processing and the optical arrangement is presented. Based on the experimental data, it can be show that this simple, laser-based strain sensor can be used successfully for the determination of mechanical and thermal strains up to temperatures of about 1200°C. Using a special data-processing procedure, it was feasible to minimize decorrelation effects caused by changes in the specimen surface due to, for example, slipband and microcrack formation, surface oxidation and phase transformation and, thus, measure large mechanical strains. The strain resolution for the selected setup was about 20 microstrains depending on the testing parameters.
84 citations
TL;DR: In this paper, an experimental configuration is described in which the complete state of stress and strain in the specimen are determined through direct experimental measurement, without a priori constitutive assumptions with regard to the material behavior.
Abstract: An experimental configuration is described in which the complete state of stress and strain in the specimen are determined through direct experimental measurement, without a priori constitutive assumptions with regard to the material behavior. Moreover, the control of the deformations is such that the deformations are always stable. Design considerations in implementing such an experimental configuration and applications to the investigation of the multiaxial constitutive behavior in materials are also described. An-example of the implementation is demonstrated using Al 6061-T6 alloy.
62 citations
TL;DR: In this paper, a novel dynamic friction experiment using the Kolsky bar concept was developed, which is complementary to the plate impact and other macroscopic friction experiments in the sense that sliding velocities and pressures not attainable otherwise can be investigated.
Abstract: A novel dynamic friction experiment using the Kolsky bar concept was developed. The technique is complementary to the plate impact and other macroscopic friction experiments in the sense that sliding velocities and pressures not attainable otherwise can be investigated. The experimental results reported in this article show that the technique provides accurate and repeatable measurement of time-resolved friction. The apparatus is simpler and easier to operate than the plate impact facility. However, it cannot achieve the same level of contact pressure. Several material pairs have been investigated. In particular, the kinetic friction coefficient of Ti-6Al-4V sliding against WC/Co (cermet) and 4340 steel sliding against WC/Co were measured and compared with the values reported by Prakash and Clifton in 1993. Atomic force microscopy is used to characterize the surface topography before and after the friction tests.
56 citations
TL;DR: In this article, the same shot-peening treatment was applied to five steels with different mechanical properties, and the induced residual stress profiles were analyzed using X-ray diffraction and incremental hole drilling (IHD).
Abstract: The same shot-peening treatment was applied to five steels with different mechanical properties. The induced residual stress profiles were analyzed using X-ray diffraction and incremental hole drilling (IHD). The results of both techniques showed that IHD can still be successfully used for measuring shot-peening residual stresses, even if these exceed the yield strength of the bulk material. Expected errors due to the plasticity effect are reduced by the strain hardening of the surface. For an assessment of the reliability of IHD data, strain-hardening variation was quantified by microhardness measurements to estimate the yield strength of the plastified layer. All the main calculation methods for IHD were applied. The results were compared and discussed with respect to the characteristics of each method.
54 citations
TL;DR: In this article, a finite element code ABAQUS is used to simulate the quenching of aluminum alloy 7010 in an attempt to predict the residual stress distribution that de- velops in simple shapes.
Abstract: Precipitation-hardened aluminum alloys gain their high strength through heat treatment involving a severe quenching operation, which can have the adverse effect of in- troducing residual stresses. The finite element code ABAQUS is used to simulate the quenching of aluminum alloy 7010 in an attempt to predict the residual stress distribution that de- velops in simple shapes. The rate of heat transfer from the material is determined using the finite element method to pre- dict the heat transfer coefficient from surface cooling curves achieved experimentally. The flow stress of the material is as- sumed to be strain rate dependent and to behave in a perfectly plastic manner. The predicted residual stress magnitudes and directions are compared to values determined using the hole- drilling strain gage method and the X-ray diffraction technique. KEY WORDS—residual stress, aluminum alloy, forging, solu- tion heat treatment
51 citations
TL;DR: The torsional split Hopkinson bar is used for testing materials at strain rates above 104s−1 as mentioned in this paper, which is an order of magnitude higher than is typical with this technique, is obtained by using very short specimens.
Abstract: The torsional split Hopkinson bar is used for testing materials at strain rates above 104s−1. This strain rate, which is an order of magnitude higher than is typical with this technique, is obtained by using very short specimens. Strain rates of 6.4×104s−1 have been achieved with specimens having a gage length of 0.1524 mm. Results from tests on 1100 aluminum show an increase in rate sensitivity as the strain rate increases.
44 citations
TL;DR: In this paper, an experimental facility has been developed that is capable of generating any combination of tensile and/or compressive forces on three mutually orthogonal axes of a cruciform-shaped composite specimen.
Abstract: An experimental facility has been developed that is capable of generating any combination of tensile and/or compressive forces on three mutually orthogonal axes of a cruciform-shaped composite specimen. Using this computer-controlled test facility, any stress ratio in biaxial (σ1-σ2) or triaxial (σ1-σ2-σ3) stress space can be evaluated. A description of this electromechanical testing facility, including the reaction frame, test fixture, computer control system and instrumentation is included. Once fully assembled, uniaxial, biaxial and triaxial tests were performed on aluminum and on a carbon/epoxy composite laminate to evaluate the performance of the test facility. Using the data generated from these tests, the performance of many aspects of the triaxial testing facility, including the intra-axis alignment, automated computer testing algorithms, data acquisition algorithms, calibration values and machine compliance, was evaluated. The overall very acceptable performance of the triaxial testing facility is believed to have been demonstrated.
TL;DR: In this paper, experimental modal analysis of a tire was carried out and mode shapes in the radial, tangential and lateral directions of the tire under radial and tangential excitation, respectively, were obtained for the first time.
Abstract: Experimental modal analysis of a tire was carried out. Mode shapes in the radial, tangential and lateral directions of the tire under radial and tangential excitation, respectively, were obtained for the first time. The consistency of tire experimental modal frequencies in three directions was observed after careful design and adjustment of the test method. This indicates the accuracy of the experiments. The phenomena discovered in this experimental study, such as the mode shapes of the rim and the complex modes of the tire, are discussed in detail. The modal parameters acquired from experimental modal analysis of the tire can be used for the modeling of tire dynamics.
TL;DR: In this article, a cure-referencing method (CRM) is proposed to measure the residual strains associated with residual stresses on the surface of composite panels by replicating diffraction gratings onto the composite specimens during the autoclave during cycle.
Abstract: This paper describes the details of a novel procedure called the cure-referencing method (CRM) to measure the strains associated with residual stresses on the surface of composite panels The CRM involves the replication of diffraction gratings onto the surface of composite specimens during the autoclave during cycle Residual strains associated with the curing process are measured using moire interferometry at room temperature after the specimens have been taken out of the autoclave The procedures for both the grating replication and the moire interferometry experiment are described in detail A method of high-temperature moire interferometry was developed to resolve the residual strains due to thermal expansion from those due to chemical matrix shrinkage and stress relaxation These procedures are demonstrated on unidirectional and multidirectional laminates and on woven textile composites
TL;DR: In this article, the shape inaccuracies of inflatable antennas and the potential shape control of the surface of those structures are investigated, which is due to geometric nonlinear deformation.
Abstract: The shape inaccuracies of inflatable antennas and the potential shape control of the surface of those structures are investigated. Surface shape inaccuracies are due to geometric nonlinear deformation. Correcting the shape of these inflatables focused on the integration of piezopolymer actuators on the membranes. The out-of-plane displacements of a membrane structure were assessed with the shadow moire method. The experimentally measured shape of the structure confirmed the extent of deviation from the ideal optical surface, a paraboloid of revolution. Active control of the shape of the membrane was tested using a piezoelectric material, polyvinylidene fluoride (PVDF). The deformation caused by actuation of the membrane structure was evaluated using electronic speckle pattern interferometry. An analytical solution was developed to verify the extent of shape correction that can be achieved by embedded PVDF actuators. It was confirmed that micron-level shape corrections are possible for future space-based sensors that use inflatable antennae technology.
TL;DR: In this article, a precracked, three-point bend specimen is loaded by a transmitter bar that is impacted by a striker bar fired from a gas gun, and a simple quasi-dynamic analysis model for deducing the fracture toughness for a running crack is presented, and the results are compared with independent measurements.
Abstract: The boundary and loading conditions in many dynamic fracture test methods are frequently not well defined and, therefore, introduce a degree of uncertainty in the modeling of the experiment to extract the dynamic fracture resistance for a rapidly propagating crack. A new dynamic fracture test method is presented that overcomes many of these difficulties. In this test, a precracked, three-point bend specimen is loaded by a transmitter bar that is impacted by a striker bar fired from a gas gun. Different levels of energy can be imparted to the specimen by varying the speed and length of the striker to induce different crack growth rates in the material. The specimen is instrumented with a crack ladder gage, crack-opening displacement gage and strain gages to develop requisite data to determine toughness. Typical data for AISI 4340 steel specimen are presented. A simple quasi-dynamic analysis model for deducing the fracture toughness for a running crack from these data is presented, and the results are compared with independent measurements.
TL;DR: In this article, the authors developed an intelligent hybrid method for the automatic detection and elimination of randomly incorporated errors into known correct finite element displacement fields using a variational principle minimizing the experimental measurement errors.
Abstract: In a previous study, to minimize or eliminate the errors and noises associated with a full-field experimental measurement and subsequent fringe analysis such as moire interferometry, the authors derived a variational principle minimizing the experimental measurement errors. Furthemore, on the basis of this variational principle, the authors developed an intelligent hybrid method. In several test simulations, the method has demonstrated the automatic detection and elimination of randomly incorporated errors into known correct finite element displacement fields. In this study, a fringe analysis method is developed together with the two-dimensional fast Fourier transform method. Then, experimentally recorded moire fringe patterns are analyzed by the fringe analysis method. The conventional and intelligent hybrid analyses are carried out using the analyzed fringe information as input data. The present method verifies the automatic detection of experimental errors and noises, and the simultaneous automatic elimination of those experimental errors. This method also makes it possible to obtain a fairly smooth visualization of higher order information such as the stress and strain distributions.
TL;DR: In this article, two explosively loaded cylindrical shell experiments were conducted to provide experimental data for benchmarking numerical codes, where each shell was subjected to internal high-explosive detonations, which caused it to expand outwardly at strain rates on the order of 104 s−1.
Abstract: Two explosively loaded cylindrical shell experiments were conducted to provide experimental data for benchmarking numerical codes. Each shell was subjected to internal high-explosive detonations, which caused it to expand outwardly at strain rates on the order of 104 s−1. At approximately 150 percent strain, multiple plastic instabilities appeared on the surface of these shells in a quasi-periodic pattem. These instabilities continued to develop into bands of localized shear and eventually formed cracks before causing the shell to fragment. Diagnostic equipment on these experiments included a Fabry-Perot interferometer and a fast-framing camera. The experiments and the data obtained from the diagnostic equipment are discussed and illustrated.
TL;DR: In this article, a large ensemble of calculated biaxial stress-relief displacement fields was used to estimate the plane stress magnitudes from selected fringe positions using a stochastic, iterative least squares minimization approach.
Abstract: Speckle interferometric fringe patterns record stress-relief displacements induced by the drilling of blind-holes into prestressed objects. The quantitative determination of residual stress state from such stress patterns is difficult because of the ambiguity in the order of the observed fringes. The plane stress magnitudes are provided directly from selected fringe positions using a stochastic, iterative least squares minimization approach. The inversion requires prior knowledge of the experimental geometry and an appropriate uniaxial stress-relief displacement basis function derived from three-dimensional finite element calculations. Superpositioning of the rotated and scaled displacement basis functions allows the stress-relief relaxation for any biaxial state of stress to be determined. In this paper, fringe patterns were forward modeled from a large ensemble of calculated biaxial stress-relief displacement fields. Inversion of these noise-free fringe patterns reproduced the biaxial stresses with negligible error. Analysis of more realistic fringe patterns that include speckle noise gave stress magnitude errors that diminished rapidly with the number of selected points to better than 3 percent for 100 points. Sensitivity of the optical method is influenced by a number of factors, but the ensemble of model fringe patterns studied indicates that the stress magnitudes (nomalized with respect to the material's Young's modulus) from 3×10−4 to 10−2 can accurately be determined with visible laser radiation. The method is amenable to automation and can easily be extended to study near surface gradients in the residual stresses or applied to other optical recording techniques such as moire and phase-shifting interferometry.
TL;DR: In this article, the experimental technique of remote laser Raman microscopy is used for the in situ measurement of K in Kevlar 49 fiber/epoxy composite plates containing a circular hole.
Abstract: When designing composite materials, the presence of stress concentration at locations such as circular nothces is unavoidable. Such locations in structural elements arise from joints required to form a structure. The stress concentration, observed around the notch, is quantified by the stress concentration factorK. This quantity is normally calculated analytically and/or numerically and is an important design parameter. In this work, the experimental technique of remote laser Raman microscopy is used for the in situ measurement ofK in Kevlar 49 fiber/epoxy composite plates containing a circular hole. The results obtained by this technique are compared with those calculated analytically and by finite element analysis. Both analytical and numerical methods underestimate the experimental results for maximumK by approximately 10 percent, which is considered reasonable within experimental error. In addition, very good agreement between analytical and experimental data is obtained for the decay of the stress concentration factor as a function of distance from the edge of the hole. The numerical results, however, overestimate the decayK with distance from the notch boundary and only converge at relatively large distances.
TL;DR: In this paper, a thermal analysis of surface temperature measurements of a mechanically loaded cylindrical specimen is presented, where the model is modeled as an infinite cylinder, suddenly exposed to a uniformly distributed volumetric heat source.
Abstract: Infrared temperature-sensing techniques have the major advantages of virtually no interference of the sensor with the sensed phenomenon and fast inherent response. On the other hand, infrared temperature sensing, as a superficial measurement technique, does not indicate the specimen's core temperatures, and hence a complementary thermal analysis is required. A thermal analysis of surface temperature measurements of a mechanically loaded cylindrical specimen is presented. The specimen is modeled as an infinite cylinder, suddenly exposed to a uniformly distributed volumetric heat source. This heat source results from the conversion of mechanical energy into thermal energy. A closed-form solution is obtained and numerical examples are given for metallic and polymeric specimens. The current analysis provides the upper boundaries for temperature differences between the core and the surface temperatures when compared with the actual problem of a finite specimen. It is shown that surface temperature measurement is a good indication of the core temperature for metallic specimens but may lead to some poor results in the case of polymeric specimens. It is found that the transient thermal response of the infinite cylinder to sudden heating behaves like a first-order process. In the case of cyclic loading, the typical time scale of loading is found to be at least two orders of magnitude shorter than the typical time scale of heat transfer. Hence, the specimen is affected by the average power of heat generation, and not by the instantaneous effect of heating within a single loading cycle.
TL;DR: In this article, the authors determine the shear strain component by observing the rotation of the moire fringes in close proximity to the hole, and compared the results of experiments on a specimen containing a model residual stress distribution.
Abstract: The use of interferometric moire and hole drilling to determine residual stress has been well reported and accepted for stress fields whose principal directions can be predicted well enough to permit the moire grids to be aligned with the principal strain axes. When the principal strains do not align themselves with the grid axes, a third strain component can be obtained by working with the diagonal pitch of the moire grid, but this requires resetting the optical bench to the lower frequency. Diffraction efficiency is lost, with an additional loss in sensitivity. In this paper, the authors determine the shear strain component by observing the rotation of the moire fringes in close proximity to the hole. The results of experiments on a specimen containing a model residual stress distribution are presented and compared with the theoretical prediction. Finally, the isothetic contours, based on elastic theory, were computed and plotted for several cases to verify this proposition. These results and the expected residual stress distribution are also compared to the experimentally obtained moire fringes.
TL;DR: In this paper, a novel experimental technique for imposing proportional dynamic confining pressure on specimens subjected to high strain rate compression was developed, where the axial compression is provided by an aluminum split Hopkinson pressure bar (SHPB).
Abstract: A novel experimental technique for imposing proportional dynamic confining pressure on specimens subjected to high strain rate compression was developed. A description of the experimental technique and experimental results on two polymeric materials are presented. The axial compression is provided by an aluminum split Hopkinson pressure bar (SHPB). The test section of the SHPB, together with the specimen, is sealed inside a small, fluid-filled pressure vessel. Upon axial loading, the shortened specimen results in a reduction in fluid volume, thereby generating lateral confining pressure on the specimen. This dynamic confining pressure is proportional to the axial loading on the specimen, with the proportionality depending on the properties and dimensions of the fluid and the specimen. Experimental results show that under dynamic confinement, the compressive strength of soft specimens increases significantly even at low strains as compared with unconfined cases at high strain rates.
TL;DR: In this article, the application of the Fourier transform to photoelasticity was used in the evaluation of the retardation using a carrier system of fringes, where the error is small if the angle between the principal stresses in the model and in the carrier is less than 25 deg.
Abstract: The application of the Fourier transform to photoelasticity was used in the evaluation of the retardation using a carrier system of fringes. In photoelasticity, the light intensity from the analyzer in a circular polariscope depends on both the retardation (isochromatics) and the isoclinic parameter. The theoretical analysis shows that the angle between the principal stresses in the model and in the carrier system of fringes influences the evaluation of the retardation (isochromatics), as occurs when misaligned compensators (namely, Babinet) are used. As a consequence, this method may not be applied as a full-field technique, although the error is small if the angle between the principal stresses in the model and in the carrier is less than 25 deg. Numerical simulations and experimental tests were conducted to corroborate this prediction.
TL;DR: In this paper, the axial, circumferential and shear strains of a round tension test specimen in a cylindrical coordinate system are determined by differentiating the axials and circumferent displacements in the axially oriented directions.
Abstract: Stereo vision is used to measure the strain field of a round tension test specimen in a cylindrical coordinate system. Initially, the displacement fields of the specimen are measured relative to a world coordinate system erected by the stereo vision. Through coordinate transformations, the measured displacement fields expressed in world coordinates are then converted to the displacement fields expressed in cylindrical coordinates. By differentiating the axial and circumferential displacements in the axial and circumferential directions, the axial, circumferential and shear strains are determined. Results indicate that the measured mean value of the axial strains is in good agreement with the measurements of the extensometer and the strain gage. The Poisson's ratio obtained by the circumferential and axial strains is close to .33 in the elastic state. The mean error of the computed shear strain is approximately .03 percent in the smaller elastic deformation and .08 percent in the larger plastic deformation.
TL;DR: In this article, an experimental approach to two-dimensional, viscoelastic, steadily moving rolling contact is described, where photoviscoelastic technique is employed for the analysis of rolling contact stresses between a viscous plate and a rigid rolling cylinder in which the principal axes of stress, strain and birefringence are not coincident with each other.
Abstract: An experimental approach to two-dimensional, viscoelastic, steadily moving rolling contact is described. The photoviscoelastic technique is employed for the analysis of rolling contact stresses between a viscoelastic plate and a rigid rolling cylinder in which the principal axes of stress, strain and birefringence are not coincident with each other. Using an elliptically polarized white light, the distribution of isochromatic fringe order and the principal axes of birefringence at an instant are determined from a single photoviscoelastic image. The time variations of the differences of the principal stresses and strains, as well as their directions, are obtained by use of the optical constitutive equations of photoviscoelasticity. The experimental results involving the time variation of the stresses around the contact surface and their distributions are analyzed.
TL;DR: A round-robin test of X-ray residual stress determination was performed by the Groupement Francais d'Analyse des Contraintes and involved 16 laboratories.
Abstract: A round-robin test of X-ray residual stress determination was performed by the Groupement Francais d'Analyse des Contraintes and involved 16 laboratories. The standard deviation of the measurements was about 36 MPa, but a posttreatment of the raw data with the same soft-ware reduced the dispersion to 19 MPa. Analysis of the uncertainty sources (goniometer alignment, operator, counting statistics, nonlinearity of the material, etc.) revealed that the main sources come from the data treatment and the operator.
TL;DR: In this article, the variation of axial strain over the cross section of an elastic cylinder as a transient compressive pulse propagates longitudinally along the cylinder was analyzed in the frequency domain and compared with theoretical predictions for first-mode propagation as derived from Pochammer-Chree analysis.
Abstract: Experimental studies were conducted on the variation of axial strain over the cross section of an elastic cylinder as a transient compressive pulse propagates longitudinally along the cylinder. Results from perimeter-mounted strain gages are analyzed in the frequency domain and compared with theoretical predictions for first-mode propagation as derived from the Pochammer-Chree analysis. Excellent agreement is found between the experimental and theoretical results for low to moderate frequencies\((0< \frac{{\omega a}}{{2\pi C_0 }}< 0.4)\).
TL;DR: In this paper, a new configuration for compression-shear soft-recovery experiments is presented, which is used to investigate various failure mechanisms during dynamic multiaxial loading of an Al2O3/SiC nanocomposite and TiB2.
Abstract: A new configuration for compression-shear soft-recovery experiments is presented. This technique is used to investigate various failure mechanisms during dynamic multiaxial loading of an Al2O3/SiC nanocomposite and TiB2. Velocity profiles of the target surface are measured with a variable sensitivity displacement interferometer, yielding normal and transverse velocity-time histories. A dynamic shear stress of approximately 280 MPa is obtained, in the Al2O3/SiC nanocomposite, for an imposed axial stress of about 3.45 GPa on a 540 μm thick sample. This dynamic shear stress is well below the value predicted by elastic wave propagation theory. This could be the result of stress-induced damage and inelasticity in the bulk of the sample or inelasticity on the sample surface due to frictional sliding. To gain further insight into the possible failure mechanisms, an investigation of compression-shear recovery techniques, with simultaneous trapping of longitudinal and lateral release waves, is conducted.
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TL;DR: In this paper, the authors performed deep punching experiments on PMMA (polymethyl methacrylate) using cylindrical-shaped punches with conical and hemispherical noses.
Abstract: The authors performed deep punching experiments on PMMA (polymethyl methacrylate) using cylindrical-shaped punches with conical and hemispherical noses. The test samples cracked when no lateral confinement was provided. Application of proper lateral confinement suppressed the cracks. The punching force recorded from the experiments correlates very well with cavity expansion theory. Because the use of a single friction coefficient gives excellent agreement between theory and experiments for two different-shaped punches, the authors propose deep punching as a new technique to measure the friction coefficient.
TL;DR: In this paper, the stiffness properties of typical laminated composite tubes from dynamic tests are identified by a technique of model updating, based on the minimization of the eigensolution residuals (sensitivity method).
Abstract: The identification of the stiffness properties of typical laminated composite tubes from dynamic tests is presented. Unknown coefficients are identified by a technique of model updating. The fomulation is based on the minimization of the eigensolution residuals (sensitivity method). Errors of generalized masses are considered. The technique allows for the simultaneous identification of several properties from a single test. Stiffness properties of extension, bending/twisting and transverse shear are identified. Important points of the model updating of tubes in dynamics are addressed: potential energy evaluation, placement of sensors and the problem of multiple eigenvalues. Results obtained by numerical simulation show the efficiency of the proposed method.