Surface Strain Measurements Research Articles

Deformation Measurements and Material Property Estimation of Mouse Carotid Artery Using a Microstructure-Based Constitutive Model

A series of pressurization and tensile loading experiments on mouse carotid arteries is performed with deformation measurements acquired during each experiment using three-dimensional digital image correlation. Using a combination of finite element analysis and a microstructure-based constitutive model to describe the response of biological tissue, the measured surface strains during pressurization, and the average axial strains during tensile loading, an inverse procedure is used to identify the optimal constitutive parameters for the mouse carotid artery. The results demonstrate that surface strain measurements can be combined with computational methods to identify material properties in a vascular tissue. Additional computational studies using the optimal material parameters for the mouse carotid artery are discussed with emphasis on the significance of the qualitative trends observed.

Maxillary Fragment Stabilization After Le Fort I Fracture With 1 Screw Pair per Plate

The aim of the present study was to determine whether plates with only 1 screw pair can be used for Le Fort I fracture management. Good postoperative results motivated the direct application of mandible fixation principles to the fractured midface region without additional experimental research. However, the amount and distribution of the forces in the midface region is different from those on the mandible. Testing was conducted on plastic anatomic models. The validity of the experimental model was tested before the fixation techniques were compared. Standard miniplates and miniscrews were used for fixation of the maxilla. The model surface strain analysis was conducted using the noncontact object grating method, which enabled the surface strain measurement without direct influence on the measured model. In 2 screw pair fixation, the outer screw pair has little effect on the local strain distribution, but it lowers the contact forces along the crack. One screw pair fixation is stable enough for fixation, but it has a greater strain peak at the crack edges. Our results showed that 1 screw pair per plate was enough for stable fixation, and 2 or more screw pairs should only be used when the bone fragment at the fracture site cannot sufficiently transmit forces along the crack.

Direct determination of cohesive stress transfer during debonding of FRP from concrete

Interface cohesive stress transfer between FRP and concrete during debonding is typically obtained using measured surface strains on the FRP, along the direction of the fibers. The cohesive material law is derived under a set of assumptions which include: (a) the bending stiffness of the FRP laminate is insignificant with respect to that of the concrete test block; (b) the strains in the bulk concrete produced by debonding are negligible, thus concrete substrate can be considered rigid; (c) there is stress transfer between FRP and concrete through the FRP–concrete interface which is of zero thickness; and (d) the axial strain in the FRP composite is uniform across its thickness. In this paper, a test procedure for directly obtaining the through-thickness strains in the FRP and the concrete substrate during cohesive stress transfer associated with debonding is presented. The displacement and strain fields are measured on the side of a direct-shear specimen with the FRP strip attached on the edge. Based on the experimental results, the influence of the assumptions which have been introduced to determine the cohesive law is discussed. Within the stress transfer zone there is a sharp gradient in the shear strain. The location of the interface crack within the stress transfer zone and the cohesive stress transfer during the propagation of the interface crack are determined.

The Biomechanics of a Validated Finite Element Model of Stress Shielding in a Novel Hybrid Total Knee Replacement

This study proposes a novel hybrid total knee replacement (TKR) design to improve stress transfer to bone in the distal femur and, thereby, reduce stress shielding and consequent bone loss. Three-dimensional finite element (FE) models were developed for a standard and a hybrid TKR and validated experimentally. The Duracon knee system (Stryker Canada) was the standard TKR used for the FE models and for the experimental tests. The FE hybrid device was identical to the standard TKR, except that it had an interposing layer of carbon fibre-reinforced polyamide 12 lining the back of the metallic femoral component. A series of experimental surface strain measurements were then taken to validate the FE model of the standard TKR at 3000 N of axial compression and at 0 degreeof knee flexion. Comparison of surface strain values from FE analysis with experiments demonstrated good agreement, yielding a high Pearson correlation coefficient of R(2)= 0.94. Under a 3000N axial load and knee flexion angles simulating full stance (0O degree, heel strike (200 degrees, and toe off (600 degrees during normal walking gait, the FE model showed considerable changes in maximum Von Mises stress in the region most susceptible to stress shielding (i.e. the anterior region, just behind the flange of the femoral implant). Specifically, going from a standard to a hybrid TKR caused an increase in maximum stress of 87.4 per cent (O0 degree from 0.15 to 0.28 MPa), 68.3 per cent (200 degrees from 1.02 to 1.71 MPa), and 12.6 per cent (600 degrees from 2.96 to 3.33 MPa). This can potentially decrease stress shielding and subsequent bone loss and knee implant loosening. This is the first report to propose and biomechanically to assess a novel hybrid TKR design that uses a layer of carbon fibrereinforced polyamide 12 to reduce stress shielding.

An in‐situ fluorescence‐based optical extensometry system for imaging mechanically loaded bone

The application and quantification of well-controlled tissue strains is required for investigations into mechanisms of tissue adaptation within the musculoskeletal system. Although many commercial and custom extensometry systems exist for large biological samples, integrated loading/strain measurement for small samples is not as readily available. Advanced imaging modules such as laser scanning microscopy provide in situ, minimally invasive tools to probe cellular and molecular processes with high spatiotemporal resolution. Currently, a need exists to devise loading/strain measurement systems that can be integrated with such advanced imaging modules. We describe the development and validation of a fluorescence-based, optical extensometry system directly integrated within a confocal microscopy platform. This system allows in situ measurement of surface strain and is compatible with the direct imaging of cellular processes within small bone samples. This optical extensometry system can accurately and reproducibly measure physiologically relevant surface strains (200 to 3000 microstrain) in beams machined from various well-characterized materials, including bovine femoral cortex, and in intact murine tibia. This simple system provides a powerful tool to further our investigation of the relationships between mechanical loading, fluid and solute transport, and mechanosensation within the musculoskeletal system.

Parametric Analysis Mechanical Properties of Bolted Joints

Three-dimensional finite element model of a bolted joint has been developed in the non-linear finite element code MSC.Marc and attempts were made to validate it by comparing results with those of experiments and other finite element. Issues in modeling the contact between the joint parts, which affect the accuracy and efficiency of the model, were presented. Experimental measurements of surface strains and load transfer ratio(LTR) were compared with results from finite element analysis. The results show that three-dimensional finite element model of bolted joint can produce results in close agreement with experiment. Three-dimensional effects such as bolt titling, seconding and through-thickness variations in stress and strain are well represented by such models. Three-dimensional finite element analysis was also used to study the effects of different parameters on the mechanical behaviour of single lap bolted joints. The results show that straight hole, small bolt diameter, and big hole pitch are selected first for bolted joint if other conditions allowed, and effect of bolt material on LTR of joint is small for small load. Interference and pre-stress should be strictly controlled for bolted joints in order to attain the best fatigue capability of lap joint.

E6 Measurement of 3D surface strain in soft sporting goods using athletic footwear as an exemplar(English session)

Three-dimensional photogrammetric deformation and strain mapping systems are becoming of interest to the athletic footwear industry for use in empirically-driven, targeted design of footwear. In this study we have developed a novel application of the GOM ARAMIS digital image correlation strain mapping system for measuring the surface strain experienced by a snowboard boot under conditions of dynamic loading. The methodology attempts to recreate externally valid rates and ranges of movement using an industrial robot and notionally biofidelic prosthetic limb. The methodology is applicable to other types of athletic footwear and soft sporting goods.

Application of a “concave-side rule” approach for assessing formability of stretch-bent steel sheets

In sheet forming, inhomogeneous through-thickness deformation, (e.g. due to a combined deformation of simultaneous stretching and bending when sheet material is drawn over a defined tool radius), is known to have influence on materials formability (i.e. onset of necking). Thus, it is preferable to take this influence into account when assessing the formability of sheet metal in a forming process. For that reason, in 2003 Tharett and Stoughton introduced the so-called “Concave-Side Rule” (CSR) approach to assess the formability of stretch-bent steel sheets. In this study the predictive quality of the CSR approach is analyzed. Therefore a series of Angular Stretch Bend Tests (ASBT) is performed. H340LAD (micro-alloyed steel) sheet specimens, with a thickness of 1.5 mm are stretch-bent over punches of various radii from 1 mm to 20 mm to produce different severity of bending in the test specimens. Results of optical on-line surface strain measurements of the test specimens are used to calibrate Finite-Element (FE) simulations of the ASBTs. From these FE-simulations, numerical results are used to assess the predictive quality of the CSR approach for H340LAD. The rule is found to be valid for H340LAD sheet material stretch-bent with punch radii R ≥ 10 mm. Whereas predictive quality decreases for more pronounced inhomogeneous through-thickness deformation (i.e. stretch-bending deformation using punch radii R < 10 mm).

Formability of porous tantalum sheet-metal

Over the past ten years, a novel cellular solid, Trabecular Metal™, has been developed for use in the orthopaedics industry as an ingrowth scaffold. Manufactured using chemical vapour deposition (CVD) on top of a graphite foam substrate, this material has a regular matrix of interconnecting pores, high strength, and high porosity. Manufacturing difficulties encourage the application of bending, stamping and forming technologies to increase CVD reactor throughput and reduce material wastes. In this study, the bending and forming behaviour of Trabecular Metal™ was evaluated using a novel camera-based system for measuring surface strains, since the conventional approach of printing or etching gridded patterns was not feasible. A forming limit diagram was obtained using specially fabricated 1.65 mm thick sheets. A springback coefficient was measured and modeled using effective hexagonal cell arrangements.

Quantifying nonlinear anisotropic elastic material properties of biological tissue by use of membrane inflation

Determination of material parameters for soft tissue frequently involves regression of material parameters for nonlinear, anisotropic constitutive models against experimental data from heterogeneous tests. Here, parameter estimation based on membrane inflation is considered. A four parameter nonlinear, anisotropic hyperelastic strain energy function was used to model the material, in which the parameters are cast in terms of key response features. The experiment was simulated using finite element (FE) analysis in order to predict the experimental measurements of pressure versus profile strain. Material parameter regression was automated using inverse FE analysis; parameter values were updated by use of both local and global techniques, and the ability of these techniques to efficiently converge to a best case was examined. This approach provides a framework in which additional experimental data, including surface strain measurements or local structural information, may be incorporated in order to quantify heterogeneous nonlinear material properties.

Evaluating damage in smart composite laminates using embedded EFPI strain sensors

Extrinsic Fabry-Perot interferometric (EFPI) strain sensors (SSs) were assessed for their sensing capacity and survivability via surface mounting and interior embedment in the carbon/epoxy beams. Artificial delaminations of two different sizes were used to simulate delamination. The embedded EFPI-SSs along with surface-mounted SGs were used to evaluate the effect of the delaminations on bending stiffness induced by quasi-static loading on a comparative basis. The linear responses of EFPI-SSs up to a bending strain of 0.5% were in good agreement with the interpolated strains of surface strain measurements. The embedded EFPI-SSs were able to differentiate the effect of the tensile delaminations on bending stiffness. The interior strain data from embedded EFPI-SSs were shown to be very useful to extrapolate the strain difference on both sides of the delaminations as well as deducing local stresses.

A Finite Element Analysis of a Tapered Flat Sheet Tensile Specimen

A uniaxial tension sheet metal coupon with a tapered instead of a straight gage section has been used for centering the location of diffuse neck and for measuring sheet stretchability in a non-uniform strain field. A finite element analysis of such a tensile coupon made of automotive steel sheet metals has been carried out to assess the effect of the tapered gage section geometry and material plastic strain hardening characteristics on the development of local plastic deformation pattern and local stress state, especially beyond the onset of diffuse necking but before localized necking. In particular, the finite element analysis was used in this study to evaluate the accuracy and reliability of an experimental data analysis method for estimating the post-necking effective plastic stress-strain curve based on the direct local surface axial plastic strain measurements for base metal, heat-affected zone, and weld metals of a dual-phase steel DP600. It is concluded that the estimated lower and upper bounds of the effective stress-strain curve at large strains are not satisfactory for low strain-hardening materials such as heat-affected zone and weld metals with the tapered tension coupons. A simple correction method utilizing only the additional local surface strain measurement in the transverse direction is proposed and it is shown to be effective in correcting the estimated effective stress-strain curve of dual-phase steel weld metals obtained for two tapered gage section geometries.

Accurate and continuous adhesive fracture energy determination using an instrumented wedge test

The wedge test and the related double cantilever beam test are practical methods of assessing structural adhesive fracture energy. In the former, and to a lesser extent the latter, a recognised problem is the difficulty of following the length of the growing crack, required to calculate fracture energy with any accuracy. We present a novel method of measurement of crack length that has the advantages of being accurate and allowing continuous assessment of crack-length evolution during the failure process. It is based on the attachment of a series of strain gauges to the outer surface of one of the beams constituting the adhesive assembly. Surface strain measurements are interpreted directly using simple beam theory. The method has been validated both with adhesive assemblies under failure conditions and by tests undertaken on “artificial” joints, where “bonding” is effected by clamping adherends together.

Thermal fatigue behavior of an iron-based laser sintered material

Direct metal laser sintering is a rapid manufacturing technique to make intricate and near net-shaped parts. An iron-based laser sintered metal was studied to evaluate its thermal fatigue properties. The test was performed using cylindrical specimens in a high power induction heating system equipped with a laser strain gauge for a contactless surface strain measurement. Initiation of thermal fatigue cracks occurred preferentially at pores and layer interfaces, while propagation of cracks followed along phase boundaries and thin inter-dendritic phases and showed an inter-granular fracture. By using the fundamental Fourier equation for heat conduction, the temperature cycle was modeled and calculated. A thermo elastic ideal plastic model was used to deduce the thermal stress based on surface strain experimentally measured. Finally, the temperature distribution, thermal stresses and mechanical strains were discussed with respect to thermal fatigue damage.

10204 表面ひずみ測定による回転曲げの疲労損傷検出(強度特性と評価,一般講演)

10204 表面ひずみ測定による回転曲げの疲労損傷検出(強度特性と評価,一般講演)

Investigation on Failure Behavior of Unflawed Steel Cylindrical Pressure Vessels Using FEA

Finite element analysis (FEA) has been carried out utilizing the ANSYS software package to assess the failure of thick and thin‐walled steel cylindrical pressure vessels. A simple experimental stress analysis (ESA) procedure is described to evaluate the stress components on inner and outer surfaces of the vessels under internal pressure from the measured surface strains. The procedure is validated considering the strain values of FEA for the applied pressure as measured quantities and obtained the corresponding stress components considering the stress‐strain data of the material from ESA and compared with those of FEA results. Failure pressure estimates from FEA (based on the global plastic deformation) were found to be in good agreement with test results of thin as well as thick‐walled cylindrical vessels made of ductile steel materials.

Understanding site-specific residual strain and architecture in bovine cortical bone

Living bone is considered as adaptive material to the mechanical functions, which continually undergoes change in its histological arrangement with respect to external prolonged loading. Such remodeling phenomena within bone depend on the degree of stimuli caused by the mechanical loading being experienced, and therefore, are specific to the sites. In the attempts of understanding strain adaptive phenomena within bones, different theoretical models have been proposed. Also, the existing literatures mostly follow the measurement of surface strains using strain gauges to experimentally quantify the strains experienced in the functional environment. In this work, we propose a novel idea of understanding site-specific functional adaptation to the prolonged load in bone on the basis of inherited residual strains and structural organization. We quantified the residual strains and amount of apatite crystals distribution, i.e., the degree of orientation, using X-ray diffraction procedures. The sites of naturally existing hole in bone, called foramen, are considered from bovine femur and metacarpal samples. Significant values of residual strains are found to exist in the specimens. Trends of residual strains noted in the specimens are mostly consistent with the degree of orientation of the crystallites. These features explain the response behavior of bone to the mechanical loading history near the foramen sites. Preferential orientation of crystals mapped around a femoral foramen specimen showed furnished tailored arrangement of the crystals around the hole. Effect of external loading at the femoral foramen site is also explained by the tensile loading experiment.

Failure analysis of triaxial braided composite

This study focuses on the description of damage and failure behaviour of triaxial braided carbon/epoxy composites under tension. The tensile tests were instrumented with optical surface strain and acoustic emission measurements. Damage was observed using X-ray and microscopy. The damage develops in two stages: (1) intra-yarn cracking: increase of the crack density and crack length, (2) local inter-yarn delamination and conjunction of the intra-yarn cracks. Statistics of crack sizes at both stages were collected and the 3D geometry of cracks was reconstructed. A finite element model of the unit cell of the textile reinforcement is used to predict damage initiation and crack orientation using Puck’s criterion. Progressive damage and stiffness deterioration is modelled using the degradation scheme of Murakami–Ohno and the damage evolution law of Ladeveze, applied to the average stress state of the yarns. Good agreement with experimental damage initiation threshold and non-linear tensile diagrams is found both for loading in fibre and off-axis directions.

EDITORIAL

This is a special issue on ‘Digital Holography and Speckle Interferometry’. The papers of this issue were presented at the symposium on ‘Digital Holography – Exploring Possibility of Using Digital Holography for Experimental Mechanics’, organised by the authors at the ‘13th International Conference on Experimental Mechanics’ (ICEM13), Alexandroupolis, Greece, 1–6 July, 2007, chaired by Emmanuel E. Gdoutos, School of Engineering, Democritus University of Thrace, Xanthi, Greece. The call for papers of the symposium is explained in the following: “Recent progress of digital holography makes it possible to measure various mechanical and geometrical parameters accurately and quickly without film development. This technique has the potential to replace other current techniques in the near future. This session focuses on new developments and techniques of digital holography as well as their applications to various engineering problems, industrial fields and real structures. The contributions on similar techniques such as moiré, conventional holography, speckle interferometry and related techniques will also be presented in this symposium. Please join this symposium if you have interests in digital holography and related techniques.” The history of digital holographic interferometry is not so long. Schnars and Jüptner developed direct recording of Fresnel holograms with a CCD sensor in 1993. Yamaguchi and Zhang developed phase-shifting digital holography in 1997. The system is very simple, capable of whole-field analysis and high process speed. The system is similar to the system of speckle interferometry, which is widely used in the market. It is valuable to compare these techniques. This gave impetus for the publication of this special issue on ‘Digital Holography and Speckle Interferometry’. This issue contains five papers on digital holography and three papers on speckle interferometry. The first paper on the digital holography by I. Yamaguchi et al. deals with the measurement of both position and shape of an object using dual wavelengths. Yamaguchi developed the phase-shifting digital holography. In this paper they also proposed a new method to measure object shapes using both the amplitude and phase of the averaged conjugated product of complex amplitudes recorded before and after wavelength shift of a laser diode. The position determination is related to the fourth paper by M. Fujigaki et al. The second paper by G. Sheoran et al. proposes shape measurement using dual index immersion. It also proposes speckle noise reduction using 5 by 5 median filtering which is compared with the third paper. The third paper by Y. Morimoto et al. presents the effect of window size on accuracy and spatial resolution in windowed phase-shifting digital holographic interferometry. The accuracy is of the sub-nanometre level by decreasing the effect of speckle noise, though the spatial resolution becomes worse according to the number of windows. The fourth paper by M. Fujigaki et al. proposes a method to determine the reconstruction distance using the standard deviation of the intensity on the reconstructed image. It also proposes a method to obtain the orientation of the specimen. The fifth paper by Y. Zhang et al. concerns with the terahertz digital holography for the future. It provides useful applications to biology and medical sciences. The first paper on speckle interferometry by A. Moreau et al. deals with vibration measurement by time average speckle interferometry and by Doppler vibrating. The second paper by G. Kalogiannakis et al. investigates the feasibility of shearographic imaging of acoustic cross-modulation. It was motivated by the latest advances in nonlinear laser Doppler vibrometry and nonlinear ultrasonic, The third paper by F. Chiang et al. presents a new approach to 3D surface countering and surface strain measurement using speckle gap effect. Although it is not an ordinary speckle interferometry, the digital speckle photography technique applied to a flat surface is extended to 3D surface countering and strain measurement of a human heart. In addition to the above eight papers, a plenary paper of ICEM13 on ‘Three-Dimensional Displacement Analysis by Windowed Phase-Shifting Digital Holographic Interferometry’ by Y. Morimoto et al. should be mentioned. This paper extends the method of a windowed phase-shifting digital holographic interferometry mentioned in the third paper of digital holography to analyse three-dimensional displacement components in a microscope. This paper was published in the January 2008 issue of Strain. Digital holography and speckle interferometry are useful methods for measurement of whole-field displacement and strain distributions in ordinary rough surface of structures. They are superior of strain gauges, which measure point strains. Use of whole-field methods requires standardization. The symposium on ‘Digital Holography and Speckle Interferometry’ was initially organized with Dr. Satoru Yoneyama of Aoyama Gakuin University. The authors would like to acknowledge his support. Unfortunately, he could not attend the symposium because of his movement to a new position.

A comparative study of the pin-bearing responses of two glass-based fibre metal laminates

The pin-bearing behaviour of two commercially available glass-based fibre metal laminates (FMLs), GLARE ® 2 and GLARE ® 3, is presented. Results shown include bearing stress, strain, stiffness and strength, surface strains in the vicinity of the hole, and damage progression using microscopy. The initial stiffness, the bearing strain at which non-linearity first occurs and the initial rate of stiffness loss were similar for both materials, indicating that the initial bearing behaviour of these FMLs is dominated by the metal layers. Microscopy results provided experimental evidence that delamination first occurs in FMLs as a result of interlaminar normal stresses from pin loading and not because of buckling of the metal layers. Final failure for both materials involved complete separation of layers caused by out of plane deformation. The ultimate bearing stress and strain were significantly higher for GLARE ® 2 than for GLARE ® 3, which the micrographs indicate is due to the higher bending stiffness of the reinforcing layers in GLARE ® 2, which delays out of plane deformation during the final failure sequence. Measurements of surface strains showed similar initial behaviour for both materials, in agreement with the analysis of the bearing stress–strain curves, and provided additional insight into the final failure sequence of the two materials.