Showing papers in "Experimental Mechanics in 2001"
TL;DR: In this article, a split Hopkinson bar is used to obtain compressive stress-strain data for rock materials, and the results show that the samples are in dynamic stress equilibrium and have constant strain rates over most of the test durations.
Abstract: This paper presents a split Hopkinson pressure bar technique to obtain compressive stress-strain data for rock materials. This technique modifies the conventional split Hopkinson bar apparatus by placing a thin copper disk on the impact surface of the incident bar. When the striker bar impacts the copper disk, a nondispersive ramp pulse propagates in the incident bar and produces a nearly constant strain rate in a rock sample. Data from experiments with limestone show that the samples are in dynamic stress equilibrium and have constant strain rates over most of the test durations. In addition, the ramp pulse durations can be controlled such that samples are unloaded just prior to failure. Thus, intact samples that experience strains beyond the elastic region and postpeak stresses can be retrieved for microstructural evaluations. The paper also presents analytical models that predict the time durations for sample equilibrium and constant strain rate. Model predictions are in good agreement with measurements.
386 citations
TL;DR: In this article, an imaging technique developed to study the strain localization phenomena that occur during the tension of thin, flat steel samples is presented, where the data are processed using digital speckle image correlation to derive the two in-plane components of the displacement vectors.
Abstract: This paper presents an imaging technique developed to study the strain localization phenomena that occur during the tension of thin, flat steel samples. The data are processed using digital speckle image correlation to derive the two in-plane components of the displacement vectors. The authors observe that the calculation of the intercorrelation function reveals a systematic error and propose a numerical method to limit its influence. Plastic incompressibility and thin-sheet assumptions are used to derive the third displacement component and, hence, the various strain and strain rate components. Numerous checks are presented at each step in processing the data to determine the final accuracy of the strain measurements. It is estimated that this accuracy is quite sufficient to track the inception and the development of localization. Examples of possible application are presented for mild steels whose strain localization mechanisms appear to be precocious and gradual.
298 citations
TL;DR: In this paper, a biaxial tensile device based on two deformable parallelograms was used to study the tensile behavior of fiber yarn reinforcements in aeronautic applications.
Abstract: This paper presents experimental studies on the mechanical behavior of fiber fabrics using a biaxial tensile device based on two deformable parallelograms. The cross-shaped specimens are well adapted to fabrics because of their lack of shear stiffness. Tension versus deformation curves, for different strain ratios, are obtained in the case of composite woven reinforcements used in aeronautic applications. It is shown that the tensile behavior of the fabric is strongly nonlinear due to the weaving undulations and the yarn contraction, and that the phenomenon is clearly biaxial. A constitutive model is described and identified from the experimental data. The essential role played by the yarn crushing will be pointed out.
184 citations
TL;DR: In this paper, the use of embedded optical fiber Bragg gratings to measure strain near a stress concentration within a solid structure was investigated, and it was shown that the form of the spectra in transmission varies between gages that are at different distances from the notch tip under given loading conditions.
Abstract: This paper investigates the use of embedded optical fiber Bragg gratings to measure strain near a stress concentration within a solid structure. Due to the nature of a stress concentration (i.e., the strong nonuniformity of the strain field), the assumption that the grating spectrum in reflection remains a single peak with a constant bandwidth is not valid. Compact tension specimens including a controlled notch shape are fabricated, and optical fiber Bragg gratings with different gage lengths are embedded near the notch tip. The form of the spectra in transmission varies between gages that are at different distances from the notch tip under given loading conditions. This variation is shown to be due to the difference in the distribution of strain along the gage length. By using the strain field measured using electronic speckle pattern interferometry on the specimen surface and a discretized model of the grating, the spectra in transmission are then calculated analytically. For a known strain distribution, it is then shown that one can determine the magnitude of the applied force on the specimen. Thus, by considering the nonuniformity of the strain field, the optical fiber Bragg gage functions well as an embedded strain gage near the stress concentration.
124 citations
TL;DR: In this article, the effect of constraint on brittle fracture of solids under predominantly elastic deformation and mode I loading conditions is studied using different cracked specimen geometry, the variation of constraint is achieved in this work.
Abstract: The effect of constraint on brittle fracture of solids under predominantly elastic deformation and mode I loading conditions is studied. Using different cracked specimen geometry, the variation of constraint is achieved in this work. Fracture tests of polymethyl methacrylate were performed using single edge notch, compact tension and double cantilever beam specimens to cover a bread range of constraint. The test data demonstrate that the apparent fracture toughness of the material varies with the specimen geometry or the constraint level. Theory is developed using the critical stress (strain) as the fracture criterion to show that this variation can be interpreted using the critical stress intensity factorKCand a second parameterT orA3,whereT andA3are the amplitudes of the second and the third term in the Williams series solution, respectively. The implication of this constraint effect to the ASTM fracture toughness value, crack tip opening displacement fracture criterion and energy release rateGCis discussed. Using the same critical stress (strain) as the fracture criterion, the theory further predicts crack curving or instability under mode I loading conditions. Experimental data are presented and compared with the theory.
92 citations
TL;DR: In this paper, acoustic emission (AE) monitoring of damage initiation and progression in carbon-fiber-reinforced polymer (CFRP) stay cables subject to largescale laboratory tests is presented.
Abstract: This paper presents acoustic emission (AE) monitoring of damage initiation and progression in carbon-fiber-reinforced-polymer (CFRP) stay cables subject to largescale laboratory tests. The research is part of the University of California, San Diego (UCSD), larger project on the design and construction of a new cable-stayed bridge made of advanced composites. No previous use of AE on large-size CFRP stay cables appears in the literature. Three types of cables of potential use in the UCSD composite bridge were tested at lengths ranging from 5500 mm to 5870 mm. The AE events were monitored to detect damage and provide a qualitative correlation with the type of structural failure. The tests allowed a comparative characterization of the failure behavior of the three types of cables under investigation. An additional study was performed to characterize acoustic attenuation and dispersion phenomena that are relevant to AE testing of largescale CFRP cables. It is shown that despite their large size, these cables are excellent acoustic wave guides exhibiting very low attenuation. Finally, this study shows promising results for an effective use of in situ AE for health monitoring of these structural components in service.
73 citations
TL;DR: In this paper, a force-based formula that combines four failure modes into one dimensionless equation to govern spot weld failure under general static loading conditions was proposed, and the failure modes are shear, rotation, normal and peel.
Abstract: This paper suggests a very simple, force-based formula that combines four failure modes into one dimensionless equation to govern spot weld failure under general static loading conditions. The four failure modes are shear, rotation, normal and peel. The normal separation mode and the peel mode are corresponding to mode I (opening mode). The tensile/shear mode is mode II (sliding mode), and the in-plane rotation mode is mode III (tearing mode). Test coupons and test fixtures are designed and tested to establish and verify this equation. To further verify this equation, a long difficult to understand automotive spot weld failure problem was studied. Applying finite element-calculated resultant loads to the proposed formula resulted in analytical values that correlated very well with the long time field observed spot weld failures. This analytical prediction reasonably explained the spot weld failure mechanism and provided good design directions to improve the durability of the auto structure.
68 citations
TL;DR: In this article, an optical pyrometer with nominal spot size of 290 μm and 12 μm diameter type K thermocouples was employed to measure and verify the temperature of the microsamples.
Abstract: Microsample tensile testing has been established as a means of evaluating the room temperature mechanical properties of specimens with gage sections that are tens to hundreds of microns thick and several hundred microns wide. The desire to characterize the mechanical response of materials at elevated temperatures has motivated the development of high-temperature microsample testing that is reported here. The design of specially insulated grips allows the microsamples to be resistively heated using approximately 2 V DC and currents ranging between 2 to 6 A. An optical pyrometer with nominal spot size of 290 μm and 12 μm diameter type K thermocouples was employed to measure and verify the temperature of the microsamples. The ability of the pyrometer to accurately measure temperature on microsamples of different thicknesses and with slightly different emissivities was established over a temperature range from 400°C to 1100°C. The temperature gradient along the length and thickness of the microsample was measured, and the temperature difference measured in the gage section used for strain measurements was found to be less than 6.5°C. Examples of elevated temperature tensile and creep tests are presented.
63 citations
TL;DR: In this article, a force-based failure criterion was used to predict the failure of a spot weld under large in-plane combined static loads, which fits current automotive industry needs for body shell finite element application very well.
Abstract: Under in-plane loading conditions, two independent modes contribute to the failure of a spot weld: the in-plane shear mode and the in-plane rotational mode. In this work, the failures of both modes under large static load are examined individually. To study the combined failure of these two modes, two special test coupons are designed. The first coupon contains one spot weld. The second coupon contains five spot welds. Tests conducted in this work show that a very simple force-based failure criterion can be used to predict the failure of a spot weld under large in-plane combined static loads. Current multiaxial failure theory cannot explain this combined failure. This force-based spot weld failure criterion fits current automotive industry needs for body shell finite element application very well.
62 citations
TL;DR: In this article, the effects of sloshing are computed in the time domain using Newmark's time integration scheme, and the experimental results are compared with those obtained from the present theoretical analysis, and good agreements are observed.
Abstract: This paper is concerned with the experimental studies on the sloshing response of liquid-filled containers. A three-dimensional finite element analysis is carried out for the numerical simulation of this problem. The effects of sloshing are computed in the time domain using Newmark's time integration scheme. A simple experimental setup is designed and fabricated in-house to conduct experiments for measuring some of the basic parameters of sloshing. A sensor device is especially developed to record the free-surface wave heights. Each wave height sensor is a capacitance probe that detects the change in level of liquid (water) precisely with no time lag. The sensors are used in conjunction with a signal-processing unit in which the capacitance values are transduced to a voltage signal between 0 V and 10 V. These wave height sensors simultaneously record the slosh wave height near the periphery of the container wall from 16 predetermined locations to give the free-surface profiles of liquid at desired time steps. The experimental results are compared with those obtained from the present theoretical analysis, and good agreements are observed.
58 citations
TL;DR: In this article, the authors investigated the load-deflection behavior of a composite sandwich beam in three-point bending and found that the effect of material nonlinearity on the deflection of the beam is more pronounced for sheardominated core failures in the case of short span lengths.
Abstract: The load-deflection behavior of a composite sandwich beam in three-point bending was investigated. The beam was made of unidirectional carbon/epoxy facings and a polyvinyl chloride closed-cell foam core. The load-deflection curves were plotted up to the point of failure initiation. They consist of an initial linear part followed by a nonlinear portion. A nonlinear mechanics of materials analysis that accounts for the combined effect of the nonlinear behavior of the facings and core materials (material nonlinearity) and the large deflections of the beam (geometric nonlinearity) was developed. The theoretical predictions were in good agreement with the experimental results. It was found that the effect of material nonlinearity on the deflection of the beam is more pronounced for shear-dominated core failures in the case of short span lengths. It is due to the nonlinear shear stress-strain behavior of the core. For long span lengths, the observed nonlinearity is small and is attributed to the combined effect of the facings nonlinear stress-strain behavior and the large deflections of the beam.
TL;DR: In this paper, a single image fringe projection profiling method was developed by combining an accurate camera calibration procedure and improved phase extraction procedures, which used a modified Hilbert transform with Laplacian pyramid algorithms to improve measurement accuracy.
Abstract: A single-image fringe projection profiling method suitable for dynamic applications was developed by combining an accurate camera calibration procedure and improved phase extraction procedures. The improved phase extraction process used a modified Hilbert transform with Laplacian pyramid algorithms to improve measurement accuracy. The camera calibration method used an accurate pinhole camera model and pixel-by-pixel calibration of the phase-height relationship. Numerical simulations and controlled baseline experiments were performed to quantify key error sources in the measurement process and verify the accuracy of the approach. Results from numerical simulations indicate that the resulting phase error can be reduced to less than 0.02 radians provided that parameters such as fringe spacing, random measured intensity noise, fringe contrast and frequency of spatial intensity noise are carefully controlled. Experimental results show that the effects of random temporal and spatial noise in typical CCD cameras for single fringe images limits the accuracy of the method to 0.04 radians in most applications. Quantitative results from application of the fringe projection method are in very good agreement with numerical predictions, demonstrating that it is possible to design both a fringe projection system and a measurement process to achieve a prespecified accuracy and resolution in the point-to-point measurement of the spatial (X, Y, Z) positions.
TL;DR: In this paper, the potential of using fiber Bragg grating (FBG) strain sensors to measure the torsion deformation theoretically and experimentally was studied, and the optimal direction of the FBG sensor was obtained to minimize the measurement error.
Abstract: In this paper, the authors study the potential of using fiber Bragg grating (FBG) strain sensors to measure the torsion deformation theoretically and experimentally. FBG sensors are bonded on the surface of a shaft. When the shaft is under torsion, there is strain induced in the FBG sensor and the Bragg wavelength will shift accordingly. According to the wavelength shift and photoelastic properties of the FBG sensor bonded to the shaft, the torsion deformation of the shaft can be obtained. To minimize the measurement error, the optimal direction of the FBG sensor is obtained. The influences of the orientation deviation of the FBG sensor are discussed. The feasibility of this method is demonstrated by experiment, and the test results agree well with the theoretical analysis.
TL;DR: In this paper, the transition from elastic to plastic behavior and from homogeneous to inhomogeneous plastic deformation was analyzed by means of electronic spekle pattern interferometry (ESPI).
Abstract: Uniaxial tension tests of semihard copper sheets were studied by means of electronic spekle pattern interferometry (ESPI). The setup allowed the authors to analyze in detail the transitions from elastic to plastic behavior and from homogeneous to inhomogeneous plastic deformation. In agreement with the conventional definition of the yield point for copper fully plastic behavior starded at permanent strains close to 0.005. The strain-hardening coefficient was very low at the early stage of plastic flow (“easy glide”), increasing progressively until values on the order of 0.13 to 0.14 were reached at maximum load. A this point, the appearance of unequally spaced fringes signaled the beginning of inhomogeneous deformation. With ESPI, this occurrence may thus serve as a criterion to establish the forming limit of the material.
TL;DR: In this article, a thermal barrier ceramic coating composed of an NiCoCrAIY bond coat and a ZrO2(Y2O3) top coat was measured by a four-point bending rig in the temperature range 20°C-900°C.
Abstract: Elastic properties of a thermal barrier ceramic coating composed of an NiCoCrAIY bond coat and a ZrO2(Y2O3) top coat were measured by a four-point bending rig in the temperature range 20°C–900°C. Different types of specimens (i.e., with bond coat only or with bond coat and top coat, on one side or on both sides) were employed. Test procedures were based on the theory discussed in Part 1 to enhance accuracy and to estimate confidence intervals. In particular, the method employed at high temperature was calibrated at room temperature by comparing the results with those obtained by methods with low sensitivity to layer thicknesses. For the bond coat, Young's modulus was found to be temperature independent up to about 500°C; a decreasing trend was observed above this temperature. For the top coat, a slightly temperature range examined. A possible explanation is given on the basis of phase transformation and the microstructure of the two layers. At room temperature, Poisson's ratio for the bond coat was found to be near 0.3, whereas a near zero value was measured for the top coat.
TL;DR: In this paper, an efficient and simple strain gage method for determining the stress intensities of sharp-notched strips is proposed, where the bisector of the notch angle is inclined to the edge so that the mixed-mode loading is created simultaneously at the notch tip.
Abstract: An efficient and simple strain gage method for determining the stress intensities of sharp-notched strips is proposed. The bisector of the notch angle is inclined to the edge so that the mixed-mode loading is created simultaneously at the notch tip. A theory of determining the stress intensities using strain gages is described on the basis of the two-dimensional theory of elasticity. Experiments on specimens with various notch shapes are carried out to verify the theoretical results. Experimental results are in good agreement with theoretical results.
TL;DR: In this paper, a combined system of blind hole drilling and digital speckle pattern interferometry is used to determine the magnitude of the residual stress induced in an aluminum plate subjected to uniaxial tension.
Abstract: A combined system of blind-hole drilling and digital speckle pattern interferometry that performs automated data analysis is used to determine the magnitude of the residual stress induced in an aluminum plate subjected to uniaxial tension. The authors perform a finite element analysis of the blind-hole drilling process to adjust the analytical model commonly used for residual stress determination. The relieved displacement field due to the introduction of the blind hole is determined by the evaluation of the optical phase distribution. Using more than 300 values of this displacement field, the magnitude of the residual stress is determined and compared with the applied stress value.
TL;DR: In this paper, the amplitude fluctuation electronic speckle pattern interferometry (AFESPI) method with an out-of-plane setup is employed to investigate the vibration of a cantilever square plate with a crack emanating from one edge.
Abstract: Owing to the advantages of noncontact and fullfield measurement, an optical system called the amplitude fluctuation electronic speckle pattern interferometry (AFESPI) method with an out-of-plane setup is employed to investigate the vibration of a cantilever square plate with a crack emanating from one edge. Based on the fact that clear fringe patterns will be shown by the AFESPI method only at resonant frequencies, both the resonant frequencies and the vibration mode shapes can be obtained experimentally at the same time. Three different crack locations will be discussed in detail in this study. One is parallel to the clamped edge, and the other two are perpendicular to the clamped edge. The numerical finite element calculations are compared with the experimental results, and good agreement is obtained for resonant frequencies and mode shapes. The influences of crack locations and lengths on the vibration behavior of the clamped cantilever plate are studied in terms of the dimensionless frequency parameter (λ2) versus crack length ratio (a/L). The authors find that if the crack face displacements are out of phase, a large value of stress intensity factor may be induced, and the cracked plate will be dangerous from the fracture mechanics point of view. However, there are some resonant frequencies for which the crack face displacements are completely in phase, causing a zero stress intensity factor, and the cracked plate will be safe.
TL;DR: A critical analysis of some mechanical methods employed for measuring the elastic properties of coatings is presented in this paper, where a rational basis for properly choosing test methods, transducers and layer thicknesses is provided.
Abstract: A critical analysis of some mechanical methods employed for measuring the elastic properties of coatings is presented. A rational basis for properly choosing test methods, transducers and layer thicknesses is provided. The analyzed methods, usually applied to relatively thick coatings, include four-point bending tests and the resonance technique. General relationships for the evaluation of coatings' elastic properties, derived from the multilayer beam and plate theories, are discussed. On the basis of the error propagation theory, for different combinations of materials and layer thicknesses, the influence of typical experimental errors, test setup parameters and material properties is analyzed, and sensitivity coefficients for relative errors are discussed. The critical experimental variables and their effect on measurement accuracy are highlighted, suggesting suitable conditions for selecting specimen geometry and testing conditions. A procedure for measurement at high temperature is outlined.
TL;DR: In this paper, an approach based on the acoustoelastic effect in which ultrasonic wave propagation speed is linked to the magnitude of the stresses present is presented, where the technique developed calls for the use of longitudinal waves in pulse-echo technique that propagate in a direction perpendicular to the surface of the work piece.
Abstract: In this paper, an activity aimed at developing an ultrasonic technique for evaluation of states of stress, and in the presence of gradients deriving from local effects of concentrated stress, is presented. The approach is based on the acoustoelastic effect in which ultrasonic wave propagation speed is linked to the magnitude of the stresses present. The technique developed calls for the use of longitudinal waves in pulse-echo technique that propagate in a direction perpendicular to the surface of the work piece. The technique has been applied in different experimental configurations on test specimens with concentration of stresses deriving from notches and fatigue cracks and has furnished encouraging results that highlight the potentiality of the method.
TL;DR: In this paper, the concept, methodology and instrumentation for hybrid experimental-numerical residual stress analysis in a laser weldment are presented. Butt et al. applied grating interferometry and digital speckle photography as complementary experimental methods for the determination of the initial model of residual strains and of the material properties at the various zones of a laser welding.
Abstract: The concept, methodology and instrumentation for hybrid experimental-numerical residual stress analysis in a laser weldment are presented. Grating interferometry and digital speckle photography are applied as complementary experimental methods for the determination of the initial model of residual strains and of the material properties at the various zones of a laser weldment. These data inserted into a finite element model enable one to analyze the formation of the residual stress state of the object, which is compared and modified by means of experimental data in a closed iterative loop. This full hybrid approach is tested successfully on a laser-welded steel specimen in uniaxial tensile tests.
TL;DR: In this article, a strain gage hybrid method is described for determining individual stresses on the boundary and in the neighborhood of cutouts in orthotropic composites, where few measured strain data are needed, and the measured strains originate away from the hole.
Abstract: A strain gage hybrid method is described for determining individual stresses on the boundary and in the neighborhood of cutouts in orthotropic composites. Results agree with independent measurements and finite element analysis. Few measured strain data are needed, and the measured strains originate away from the hole. Ability to determine the stresses on the edge of a cutout from nonboundary measurements recognizes the difficulties in obtaining reliable measurements very near an edge while circumventing the challenge of attempting to bond gages to the transverse curved surface of a small hole or notch. The method also alleviates the problem of not knowing a priori where the most serious stress will occur on the geometric boundary and, hence, where to locate strain gages.
TL;DR: In this article, a method for rapid two-stage dynamic-dynamic tensile loading of polymers, based on a tensile Hopkinson bar apparatus, is established, where the initial incident wave and its reflection are used to load a specimen in quick succession.
Abstract: A method for rapid two-stage dynamic-dynamic tensile loading of polymers, based on a tensile Hopkinson bar apparatus, is established. In this technique, the initial incident wave and its reflection are used to load a specimen in quick succession. Consequently, the specimen is stressed, momentarily unloaded, then reloaded until fracture. By adopting appropriate assumptions, a procedure to obtain the associated stress-strain curves for such double-stage loading is formulated. These assumptions are examined experimentally and analytically to substantiate their validity. To verify the proposed approach, a relatively rate-insensitive material, LEXAN 141 polycarbonate, was subjected to two-stage dynamic tension. The stress-strain curves obtained via the procedure established were compared with results from static loading. Favorable correlation between the two indicates that the proposed technique can be applied to the study of load history effects on the dynamic behavior of polymeric materials.
TL;DR: In this paper, the isotropic and anisotropic photoelastic experimental hybrid methods for fracture mechanics are developed, and it is demonstrated that one can precisely obtain stress intensity factors and separate the stress components of isotropics and anIsotropic plate problems from the only isochromatics.
Abstract: In this paper, the isotropic and anisotropic photoelastic experimental hybrid methods for fracture mechanics are developed. Using the photoelastic experimental hybrid method, it is demonstrated that one can precisely obtain stress intensity factors and separate the stress components of isotropic and anisotropic plate problems from the only isochromatics.
TL;DR: In this article, a carbonaceous grating technique and a total imaging technique are introduced to improve the sensitivity of the scanning electron microscope (SEM) moire method for microscopic measurements based on electron beam lithography.
Abstract: The scanning electron microscope (SEM) moire method for microscopic measurements based on electron beam lithography and an SEM has been well developed. Although it has been a reliable method, some drawbacks exist: reinforcement effects, complicated processing and low sensitivity. To improve the SEM moire method, new grating-casting techniques and a fringe-viewing technique must be developed. In this study, a carbonaceous grating technique and a total imaging technique are introduced. Accordingly, there are two techniques available for grating-casting (i.e., the carbonaceous grating technique and the existing lithography grating technique) and three techniques available for fringe viewing (i.e., the total imaging technique, the existing, monitor viewing technique and the existing photographic viewing technique). A total of six new imaging techniques of SEM moire methods are available for microscopic measurements by combining one technique from each of the two groups. This study demonstrates the feasibility of the individual techniques and discusses the characteristics and limitations of each. Based on the presented total imaging technique, the sensitivity of the moire method is only dependent on the frequency of specimen grating. Because it can be made as high as 10,000 lines/mm, the SEM moire method can achieve sensitivity as high as 0.01 percent.
TL;DR: In this paper, an analytical model is presented relating the shape of an axisymmetric liquid bridge in terms of volume, v, height, h, bounding radius, r, and contact angle, θ, to the residual force, f, resulting from the surface tension at the liquid-vapor interface.
Abstract: An analytical model is presented relating the shape of an axisymmetric liquid bridge in terms of volume,v, height,h, bounding radius,r, and contact angle, θ, to the residual force,f, resulting from the surface tension at the liquid-vapor interface. The model is based on the assumption that gravity is negligible and the surface of the liquid bridge possesses constant mean curvature. Measurements are made of the height, bounding radius, contact angle and force for known volumes of individual, axisymmetric liquid bridges between parallel plates. Force and height comparisons are made for mercury on aluminum plates, mercury on polysiloxane-coated plates and water on polysiloxane-coated plates in air for dimensionless volumes (v/r3) of 10 and 18. Comparisons with model predictions are also made for mercury bridges spanning a contact angle range between 138 deg and 150 deg. Finally, the shapes of liquid bridges are compared to analytical predictions. The results suggest that the constant mean curvature model, even when gravity is neglected, is an appropriate design tool that can be useful for specifying solder volumes and standoff heights for solder grid array packages.
TL;DR: In this article, the through-thickness distribution of moisture concentration is derived and experimentally predicted for a laminate exposed to water, based on one-dimensional diffusion theory.
Abstract: Hygric behavior of woven glass/epoxy composites is investigated by characterizing them using a novel experimental technique calledhunch-up technique. Based on one-dimensional diffusion theory, the through-thickness distribution of moisture concentration is derived and experimentally predicted for a laminate exposed to water. A procedure is prescribed to determine average axial hygric strain from the measured hunch-up distance of an axially constrained specimen exposed to water. The experimental results show that the hunch-up distance is extremely sensitive to moisture expansion. There results also give excellent confirmation to the theoretical predictions. An error analysis reveals that the hunch-up technique can reduce errors by an order of magnitude better than traditional measurement techniques.
TL;DR: In this paper, the displacement fields of a workpiece during abrasive waterjet impinging and drilling are recorded in real time and simultaneously by the moire interferometry experimentation.
Abstract: The transient state of displacement fields in the machining zone of a target material during abrasive waterjet impinging and drilling was investigated. A moire interferometry experimental setup for recording displacement fields and a dynamometer for measuring the reaction force were developed. Whole fields of surface displacement fields and the reaction force of the ceramic and polycarbonate target materials were successfully recorded when the specimen was being pierced by high-pressure abrasive waterjet (AWJ). This paper demonstrates that bothu andv displacement fields of a workpiece during AWJ drilling can be recorded in real time and simultaneously by the moire interferometry experimentation. The measured surface displacement distributions and the machining forces will be used to drive a finite element model in the second part of this investigation, in which the authors study the stress and strain state for the target material associated with the jet-materials interaction during the jet penetration process.
TL;DR: In this article, the displacement fields associated with the abrasive waterjet (AWJ) drilling process were simulated using the finite element method, and the effect of these three pressure loads and their magnitudes on the surface displacement were investigated as a function of the jet penetration depth through numerical modeling.
Abstract: In this paper, the displacement fields associated with the abrasive waterjet (AWJ) drilling process were simulated using the finite element method. A threedimensional finite element model was established, and justifiable pressure loads were used in the numerical model to simulate the AWJ drilling process. It was assumed that the pressure load in the AWJ could be resolved into three components, such as impact jet pressure, shear and normal pressure. The effect of these three pressure loads and their magnitudes on the surface displacement were investigated as a function of the jet penetration depth through numerical modeling. Using the hybrid experimental-numerical stress analysis approach, the transient state of stress and strain associated with the notch crest of the jet-induced hole at the impingement zone of the target material during AWJ piercing can be modeled numerically. It was found that the shear contributed the most in shaping the displacement contour patterns and that the jet pressure did not play a dominant role in determining theu field displacement. The jet pressure and shear had the most effect on thev field displacement contour pattern. It was demonstrated that the principal stresses at the bottom of the cavity increase as the depth of the hole increases.
TL;DR: In this paper, a novel experimental method is developed to improve the sensitivity in measuring the hygric properties of composite material, based on measuring the curvature of an unbalanced laminate introduced by the unbalanced interlaminar resultant forces.
Abstract: A novel experimental method is developed to improve the sensitivity in measuring the hygric properties of a composite material. The technique is based on measuring the curvature of an unbalanced laminate introduced by the unbalanced interlaminar resultant forces. A theoretical foundation is established for evaluating the coefficients of moisture expansion (in the longitudinal and transverse directions) and the stress-free temperature from a single set of measurements. The measurement scheme is validated with a set of experiments using two antisymmetric cross-ply laminates [O2/9O2] and [O5/9O5]. The experimental results agree with the measurements reported elsewhere. This study reveals that the sensitivity of the technique is greater than that of traditional techniques.