Strain Gauge Technique Research Articles

Enhanced magnetoelastic effect in Laves (Tb,Dy)Fe2 alloys with the joint introduction of Pr and Nd

The structural and magnetoelastic properties of (Tb0.3Dy0.7)1−x(Pr0.5Nd0.5)xFe1.93 (0 ≤ x ≤ 0.20) polycrystalline alloys have been investigated by means of X-ray diffraction (XRD), a vibrating sample magnetometer and a standard strain gauge technique. A single (Tb,Dy,Pr,Nd)Fe2 Laves phase with a cubic MgCu2-type structure is formed when x ≤ 0.12, while a small amount of impurities appear when x ≥ 0.15. The easy magnetization direction at room temperature is detected toward axis. The analysis of XRD, magnetization and magnetostriction shows that the Pr and Nd elements joint introduction into (Tb,Dy)Fe2 system can reduce the magnetocrystalline anisotropy and improve the magnetoelastic properties. The (Tb0.3Dy0.7)0.88(Pr0.5Nd0.5)0.12Fe1.93 alloy exhibits a high low-field magnetostriction λa (~314 ppm/1 kOe), a large spontaneous magnetostriction coefficient λ111 (~1710 ppm), a giant saturation magnetostriction λS (~1060 ppm) and the low magnetocrystalline anisotropy at room temperature, and may make it a promising candidate for magnetostriction applications.

Experimental measurement of gear mesh stiffness of cracked spur gear by strain gauge technique

In this paper, an experimental technique based on strain gauge has been proposed to measure the gear mesh stiffness of healthy spur gear as well as of cracked spur gear pair system. Calculation of mesh stiffness of healthy and cracked spur gear tooth are based on strain energy and strain energy release rate respectively. The location of strain gauge plays an important role in calculation of strain energy stored in gear tooth. The locations of strain gauge on gear tooth are illustrated for healthy and cracked gear. Stress intensity factor (SIF) has been calculated by strain gauge technique for calculating the stiffness of cracked pinion tooth. The effect of crack length on mesh stiffness has been investigated by strain gauge technique and results are compared with the established analytical method.

Digital image correlation for grain scale strain measurement in interstitial free high strength steel

Deformation measurement of materials and structures subjected to various loading conditions is an important task of experimental solid mechanics. Apart from the widely used point wise strain gauge technique, various full field non-contact optical methods are used for this purpose. In this work, an automated scheme to measure the grain level deformation in tensile deformed interstitial free high strength steel has been introduced. The method is based on digital image correlation technique. The proposed scheme utilised high resolution scanning electron images of the specimen surface that are sequentially captured during tensile loading. It is found that grain to grain there is large variation in deformation response at a given load. The present work also reveals point to point variation of strain within a grain interior.

Determination of KI in orthotropic laminates with double ended cracks using a single strain gage technique

Experimental determination of mode I stress intensity factor (SIF) KI in orthotropic composites is of significant importance. In this direction, single strain gage techniques that are developed for measurement of KI are based on the solutions of the single ended crack theories and those have also been tested only for single ended cracked orthotropic configurations. Although, certain limitations prevent straight forward application of these single ended crack solutions to the double ended configurations, the present investigation aims at demonstrating the use of such a single strain gage technique recently proposed by the authors to the configurations containing double ended cracks or internal cracks in orthotropic materials for the accurate measurement of KI. Importantly, the present investigation also proposes existence and determination of optimal strain gage locations in double ended cracked orthotropic plates for the accurate measurement of KI. Studies have also been carried out to understand the effect of change in geometry of the configuration on the optimal gage locations. The results of the present investigation have been observed to substantiate the theoretical formulations in terms of accurate determination of KI. Numerical results clearly show that the proposed single strain gage technique yields accurate values of KI when the gage is placed at an optimal gage location. On the contrary, highly erroneous values of KI are obtained when the gage is placed at non-optimal locations.

Structural and magnetic properties of Pr0.3Tb0.7Fe1.9-xMnx Ribbons

The structural and magnetic properties of Pr0.3Tb0.7Fe1.9-xMnx ribbons have been investigated using X-ray diffraction, vibrating sample magnetometry and the standard strain gauge technique. According to the XRD spectra, all ribbons of Pr0.3Tb0.7Fe19-xMnx demonstratea pure Laves phase, which benefits from the melt-spun technology. The Curie temperature of the Pr0.3Tb0.7Fe1.9-xMnx alloys decreases gradually from 366°C for x=0.1 to 328°C for x=0.3. Meanwhile, magnetostriction at room temperature demonstrates a maximum at x=0.1.

Effect of temperature and humidity on post-gel shrinkage, cusp deformation, bond strength and shrinkage stress – Construction of a chamber to simulate the oral environment

ObjectivesEvaluate the effect of environment on post-gel shrinkage (Shr), cuspal strains (CS), microtensile bond strength (μTBS), elastic modulus (E) and shrinkage stress in molars with large class II restorations. MethodsSixty human molars received standardized Class II mesio-oclusal-distal cavity preparations. Restorations were made with two composites (CHA, Charisma Diamond, Heraus Kulzer and IPS Empress Direct, Ivoclar-Vivadent) using three environment conditions (22°C/50% humidity, 37°C/50% humidity and 37°C/90% humidity) simulated in custom developed chamber. Shr was measured using the strain gauge technique (n=10). CS was measured using strain gauges. Half of the teeth (n=5) were used to assess the elastic modulus (E) and Knoop hardness (KHN) at different depths using microhardness indentation. The other half (n=5) was used to measure the μTBS. The composites and environment conditions were simulated in a two-dimensional finite element analysis of a tooth restoration. Polymerization shrinkage was modeled using Shr data. The Shr, CS, μTBS, KHN and E data were statistically analyzed using two-way ANOVA and Tukey test (significance level: 0.05). ResultsBoth composites had similar Shr, CS, μTBS and shrinkage stress. CHA had higher elastic modulus than IPS. Increasing temperature and humidity significantly increased Shr, CS and shrinkage stress. μTBS were similar for groups with lower humidity, irrespective of temperature, and higher with higher humidity. E and KHN were constant through the depth for CHA. E and KHN values were affected by environment only for IPS, mainly deeper in the cavity. Shrinkage stress at dentin/composite interface had high inverse correlation with μTBS. Shrinkage stress in enamel had high correlation with CS. ConclusionsIncreasing temperature and humidity caused higher post-gel shrinkage and cusp deformation with higher shrinkage stresses in the tooth structure and tooth/restoration interface for both composites tested. The chamber developed for simulating the oral environment conditions will improve the realism of in vitro studies.Clinical significance Simulating oral temperature and humidity is important to better determine the biomechanical behavior of composite resin restoration. Avoiding high humidity during restorative procedures using rubber dam isolation may reduce cuspal deformation and shrinkage stress and improve the bonding strength of posterior composite restorations.

Influence of boundary conditions on the critical and failure load in the GFPR channel cross-section columns subjected to compression

The paper deals with experimental investigation and numerical analysis on influence of boundary conditions on critical load, post-buckling behaviour and failure load of compressed composite channel-section columns. The columns were made of 8-ply glass–epoxy laminate. The six different layers arrangement were considered.Tests were conducted using two test stands. In the first of them, special self-aligning grips with spherical bearings were used. In the second stand contains a stiff plate and a table. The stiff plate was mounted to the upper jaw and has only one degree of freedom (vertical movement). The table with spherical bearing which is mounted in the bottom jaw has 3 DOF (rotations about three perpendicular axes). The strain-gauges technique has been used for all tested specimens. Additionally the second stand has been equipped with the ARAMIS system for non-contact 3D displacement measurements.Numerical analysis was conducted using ANSYS software. Two models were prepared with boundary conditions corresponding to test stands.The critical load values were determined using following methods: the load vs. square of strain difference P−(ε1−ε2)2, the load vs. strain difference P−(ε1−ε2) curve inflection point method. To the failure load estimation the Tsai-Wu criterion and maximum stress criterion have been applied.

Effect of Restorative Protocol on Cuspal Strain and Residual Stress in Endodontically Treated Molars.

To evaluate the effect of the restorative protocol on cuspal strain, fracture resistance, residual stress, and mechanical properties of restorative materials in endodontically treated molars. Forty-five molars received mesio-occlusal-distal (MOD) Class II preparations and endodontic treatment followed by direct restorations using three restorative protocols: composite resin (CR) only (Filtek Supreme, 3M-ESPE), resin modified glass ionomer cement in combination with CR (Vitremer, 3M-ESPE in pulp chamber and Filtek Supreme in MOD cavity), conventional glass ionomer cement in combination with composite resin (CGI-CR) (Ketac Fil, 3M-ESPE in pulp chamber and Filtek Supreme in MOD cavity). Cuspal strain was measured using strain gauges, and fracture resistance was tested with an occlusal load. Elastic modulus (EM) and Vickers hardness (VH) of the restorative materials were determined at different depths using dynamic microhardness indentation. Curing shrinkage was measured using the strain gauge technique. The restorative protocols were also simulated in finite element analysis (FEA). The shrinkage strain, cuspal strain, EM, VH, and fracture resistance data were statistically analyzed using split-plot analysis of variance and Tukey test (p=0.05). Residual shrinkage stresses were expressed in modified von Mises equivalent stresses. Shrinkage strain values (in volume %) were Ketac Fil (0.08±0.01) < Vitremer (0.18±0.01) < Filtek Supreme (0.54±0.03). Cuspal strain was higher and fracture resistance was lower when using CR only compared with the techniques that used glass ionomer. The EM and VH of the materials in the pulp chamber were significantly lower for glass ionomer. The FEA showed that using CR only resulted in higher residual stresses in enamel and root dentin close to the pulp chamber than the combinations with glass ionomers (RMGI-CR and CGI-CR). The choice of restorative protocol significantly affected the biomechanical behavior of endodontically treated molars. Using glass ionomer to fill the pulp chamber is recommended when endodontically treated molars receive direct composite restorations because it reduces cuspal strain and increases fracture resistance.

Experimental Investigation of GFRP Laminate Thin-Walled Column Subjected to Uniform Compression

This paper presents the results of experimental investigation of thin-walled GFRP laminate columns with square cross-section subjected to uniform compression. Column under consideration are made of eight ply laminate with different quasi-isotropic layer arrangement. The following three cases of layers arrangement are taken into consideration: CS1 [45/-45/45/-45]S, CS2 [45/-45/0/0]Sand CS3 [45/-45/45/0]S. The analysed columns have the length of 250 mm and following cross-section dimensions (width × height × thickness of the wall): 82 × 82 × 2.08 mm.The main aim of experimental investigation has been to compare the way of buckling load and postbuckling behaviour determinations. The layer arrangement influence on buckling load and postbuckling stiffness have been also checked. Two different methods (P-w2method and "inflection point" method) of determining buckling forcePcrand two different measurement technique (i.e. strain-gauges technique and stereographic transformations technique) have been employed.

Numerical and experimental investigations of the post-buckling behaviour of square cross-section composite tubes

The buckling and post-buckling behaviour of thin-walled square cross-section tubes subjected to static compression is presented. The columns under consideration were made with the autoclaving technique of eight layers of a glass fibre reinforced polymer unidirectional prepreg tape. Six different arrangements of layers were taken into account. The following experimental data were collected: force–displacement relations obtained from a Zwick/Roel universal testing machine, strains at chosen points of the tube measured with a strain gauge technique, a map of deflections obtained with a non-contact 3D optical method (Aramis System, made by GOM company). All those results were used to determine buckling load and equilibrium paths in the pre- and post-buckling range. A numerical model of the analysed tube was prepared with the ANSYS software. A linear and nonlinear buckling analysis was performed. The experimental results were used to validate the proposed FEM model. An influence of the layer arrangement on the buckling and post-buckling behaviour, differences between the numerical and experimental results and the methods employed for buckling load determination are discussed.

Stresses in a Bogie Frame of a Rail Carriage

The paper presents a comparative study regarding the distribution of stresses and strains in a bogie frame, a prototype used in plants for the transportation of liquid cast iron, for a case of loading corresponding to common working operating conditions. The results of a numerical analysis carried out using the three-dimensional finite element method and those of an experimental study using the strain gauge technique were compared. Agreement between calculated and measured results obtained was good and areas of the bogie frame with maximum stress were predicted with reasonable accuracy. Knowing the most dangerous stress concentration zones, a new design optimization process could be accelerated without becoming unreliable, ensuring thus a safe transportation of cast iron by rail.

Stress distribution patterns of implant supported overdentures-analog versus finite element analysis: A comparative in-vitro study.

Aims and Objectives:The aim of this study was to asses & compare the load transfer characteristics of Ball/O-ring and Bar/Clip attachment systems in implant supported overdentures using analog and finite element analysis models.Methodology:For the analog part of the study, castable bar was used for the bar and clip attachment and a metallic housing with a rubber O-ring component was used for the ball/O-ring attachment. The stress on the implant surface was measured using the strain-gauge technique. For the finite element analysis, the model were fabricated and load applications were done in a similar manner as in analog study.Results:The difference between both the attachment systems was found to be statistically significant (P<0.001).Conclusion:Ball/O-ring attachment system transmitted lesser amount of stresses to the implants on the non-loading side, as compared to the Bar-Clip attachment system. When overall stress distribution is compared, the Bar-Clip attachment seems to perform better than the Ball/O-ring attachment, because the force was distributed better.

Non-destructive strain determination based on phase measurement and radial basis function

A method of non-destructive strain field determination based on the combination of the temporal phase measurement interferometry (TPMI) with radial basis function (RBF) was proposed in this paper. The quality of unwrapped phase obtained by TPMI was improved after RBF interpolation. Then accurate displacements can be obtained, followed by the strain components calculated by employing point-wise local least-squares fitting technique. Optimal sampling intervals of images with different sizes were given based on numerical experiments. For validation, the normal strain distributions in y direction of an aluminum plate subjected to uniform tensile loading were determined by the proposed technique and compared with values measured by strain gauge. The results are in good agreement with each other. Besides, strain distribution of a three-point bending beam with pre-notch was evaluated by the proposed method and the strain gauge technique. Comparison of the results reveals the effectiveness and feasibility of the proposed method.

Occlusal load distribution through the cortical and trabecular bone of the human mid-facial skeleton in natural dentition: A three-dimensional finite element study

Understanding of the occlusal load distribution through the mid-facial skeleton in natural dentition is essential because alterations in magnitude and/or direction of occlusal forces may cause remarkable changes in cortical and trabecular bone structure. Previous analyses by strain gauge technique, photoelastic and, more recently, finite element (FE) methods provided no direct evidence for occlusal load distribution through the cortical and trabecular bone compartments individually. Therefore, we developed an improved three-dimensional FE model of the human skull in order to clarify the distribution of occlusal forces through the cortical and trabecular bone during habitual masticatory activities. Particular focus was placed on the load transfer through the anterior and posterior maxilla. The results were presented in von Mises stress (VMS) and the maximum principal stress, and compared to the reported FE and strain gauge data. Our qualitative stress analysis indicates that occlusal forces distribute through the mid-facial skeleton along five vertical and two horizontal buttresses. We demonstrated that cortical bone has a priority in the transfer of occlusal load in the anterior maxilla, whereas both cortical and trabecular bone in the posterior maxilla are equally involved in performing this task. Observed site dependence of the occlusal load distribution may help clinicians in creating strategies for implantology and orthodontic treatments. Additionally, the magnitude of VMS in our model was significantly lower in comparison to previous FE models composed only of cortical bone. This finding suggests that both cortical and trabecular bone should be modeled whenever stress will be quantitatively analyzed.

Calf venous compliance measured by venous occlusion plethysmography: methodological aspects.

Calf venous compliance (C calf) is commonly evaluated with venous occlusion plethysmography (VOP) during a standard cuff deflation protocol. However, the technique relies on two not previously validated assumptions concerning thigh cuff pressure (P cuff) transmission and the impact of net fluid filtration (F filt) on C calf. The aim was to validate VOP in the lower limb and to develop a model to correct for F filt during VOP. Strain-gauge technique was used to study calf volume changes in 15 women and 10 age-matched men. A thigh cuff was inflated to 60 mmHg for 4 and 8 min with a subsequent decrease of 1 mmHg s(-1). Intravenous pressure (P iv) was measured simultaneously. C calf was determined with the commonly used equation [Compliance = β 1 + 2β 2 × P cuff] describing the pressure-compliance relationship. A model was developed to identify and correct for F filt. Transmission of P cuff to P iv was 100 %. The decrease in P cuff correlated well with P iv reduction (r = 0.99, P < 0.001). Overall, our model showed that C calf was underestimated when F filt was not accounted for (all P < 0.01). F filt was higher in women (P < 0.01) and showed a more pronounced effect on C calf compared to men (P < 0.05). The impact of F filt was similar during 4- and 8-min VOP. P cuff is an adequate substitute for P iv in the lower limb. F filt is associated with an underestimation of C calf and differences in the effect of F filt during VOP can be accounted for with the correction model. Thus, our model seems to be a valuable tool in future studies of venous wall function.

Experimental Validation of a Finite Element Model of an Osteoporotic Human Femoral Bone Using Strain Gauge Measurement

The complications of fractures caused by osteoporosis have a mortality rate of 15-20 % in elderly people, leading to severe physical disability and long term home care [1]. Although currently, the technology that allows us to prevent osteoporosis and fractures caused by this disease exists, the statistics are concerning and can be considered basis for further research regarding this pathology of the bone tissue. This paper aims to address this issue form an engineering perspective by achieving experimental validation of a finite element model of an osteoporotic human femoral bone using strain gauge measurement for an in vitro analysis. A Computer Aided Design (CAD) model based on a CT of a human femoral bone was then used in a numerical analysis. The material constants used are taken from the literature and have been validated experimentally by strain gauge technique.

Paleostress of the Joseon and Pyeongan Supergroups in South Korea using the New Calcite Strain Gauge (NCSG)

Limestone bodies under the tectonic environment have experienced various tectonic processes, and also changed the stress state. In this study, calcite twins found in limestones of the Joseon Supergroup and Pyeongan Supergroup in the northeastern part of the Ogcheon Belt, South Korea were measured, then the paleostress (i.e., the maximum shortening axis) was reconstructed using the new calcite strain gauge (NCSG) technique. The average twin thickness and average twin intensity increase as the total twin strain increases. We utilize the appearance of twins, the average twin thickness and average twin intensity, and the total twin strain to estimate that the observed calcite twins were produced at temperatures of < 200oC in the Joseon Supergroup and 170oC in the Pyeongan Supergroup. In the Joseon Supergroup, the dominant direction of the maximum shortening axis WNW-ESE to NW-SE; NE-SW shortening is also observed. The maximum shortening axes in the Pyeongan Supergroup are oriented NW-SE and NE-SW. The NE-SW direction of maximum shortening is associated with the occurrence of the Songrim orogeny of the Paleozoic to Early Jurassic, and the NW-SE direction of maximum shortening correlates to the Daebo orogeny of the Early Jurassic to Late Jurassic. It is thus concluded that the paleostress across the study area changed from NE-SW to NW-SE during the Mesozoic.

A new single strain gage technique for the accurate determination of mode I stress intensity factor in orthotropic composite materials

The present work proposes a new single strain gage technique for the accurate determination of mode I stress intensity factor (SIF) in orthotropic composite materials. This work also aims at showing the existence of valid or optimal gage locations for the accurate determination of SIFs in orthotropic composites. Accordingly, a finite element based general approach is developed for the estimation of such optimal gage locations. Results of numerical examples show that the proposed strain gage technique can yield highly accurate value of SIF for orthotropic laminates when the gage is placed within the valid locations.

Measuring systolic ankle and toe pressure using the strain gauge technique – a comparison study between mercury and indium-gallium strain gauges

Background. Measurement of the ankle and toe pressures are often performed using a plethysmograph, compression cuffs and a strain gauge. Usually, the strain gauge contains mercury but other alternatives exist. From 2014, the mercury-containing strain gauge will no longer be available in the European Union. The aim of this study was to compare an indium-gallium strain gauge to the established mercury-containing strain gauge. Methods. Consecutive patients referred to the Department of Clinical Physiology and Nuclear Medicine at Bispebjerg and Frederiksberg Hospitals for measurements of systolic ankle and toe pressures volunteered for the study. Ankle and toe pressures were measured twice with the mercury and the indium-gallium strain gauge in random order. Comparison of the correlation between the mean pressure using the mercury and the indium-gallium device and the difference between the two devices was performed for both toe and ankle level. Results. A total of 53 patients were included (36 male). Mean age was 69 (range, 45–92 years). Mean pressures at toe and ankle level with the mercury and the indium-gallium strain gauges were 77 (range, 0–180) mm Hg and 113 (range, 15–190) mm Hg, respectively. Comparison between the mercury and the indium-gallium strain gauge showed a difference in toe blood pressure values of − 0.7 mm Hg (SD: 7.0). At the ankle level, a difference of 2.0 mm Hg (SD: 8.6) was found. Conclusion. The two different devices agree sufficiently in the measurements of systolic ankle and toe pressure for the indium-gallium strain gauge to replace the mercury strain gauge.

Magnetostriction and thermal expansion of HoFe11−xCoxTi intermetallic compounds

The thermal expansion and magnetostriction of the HoFe11−xCoxTi (0≤x≤11) alloys have been investigated, using the strain gauge technique in the temperature range 77–600K. Both thermal expansion and thermal expansion coefficient exhibit an anomalous behaviour and Invar effect below Curie temperature (TC=516K) in sample with x=0. The increase of x in HoFe11−xCoxTi system leads to disappearing of the Invar effect and increasing of the average thermal expansion coefficient from 6.370×10−6K−1 in x=0 to 10.735×10−6K−1 in x=11 below room temperature. In addition, the spontaneous volumemagnetostriction decreases with Co content. The magnetostriction compensation point is observed in the anisotropic magnetostriction curve of all samples. The maximum value of anisotropic magnetostriction (Δλ≈50×10−6) at room temperature is observed in sample with x=9. The saturation behaviour only appears in samples with x=5, 7 and 9. In samples with x=3, 5 and 7, a noticeable volume magnetostriction (ΔV/V) is observed in low temperature due to first-order magnetisation process. Moreover, ΔV/V exhibits a large anomaly about 45×10−6 and 20×10−6 around room temperature related to spin reorientation transition in samples with x=9 and 11, respectively. The results are discussed based on the local magnetic moment model and irreducible magnetoelastic coupling modes.