Stress Analysis Technique Research Articles

New high sensitivity approach for a quantitative visualization of the continuous whole-field stress evolution in digital photoelasticity

Digital photoelasticity is a widely used technique for experimental stress analysis on mechanical models subjected to loading conditions, due to its ability to reveal the stress information through color fringe patterns and consequently demodulate it computationally to achieve a quantitative evaluation. In this process, some limitations persist, such as, expertise dependence, experimental repeatability, sensitivity to load increments, and weak performance under experimental conditions, especially in time-dependent scenarios. In response to these weaknesses, the method “Quantitative Visualization of the Continuous Whole-Field Stress Evolution” introduced the ability to perform a complete demodulation of the fringe patterns generated in time-dependent applications, achieving high performance compared to conventional photoelasticity methods. This paper proposes a new highly sensitive approach for a quantitative visualization of the continuous whole-field stress evolution in digital photoelasticity by incorporating an inverse signal process and a multi-stage strategy. The algorithm aims to ensure the performance under high fringe order conditions while exhibiting high sensitivity in cases where the maximum stress obtained is less than one fringe order. The results presented validate its effectiveness in demodulating full-field stress distributions, especially in scenarios where the loading condition induces fringe orders less than one, thus contributing to the broader applicability of digital photoelasticity.

Non-destructive Testing Techniques for Stress Analysis of Pressure Vessels

Non-destructive Testing Techniques for Stress Analysis of Pressure Vessels

Quantitative Full-Field Data Fusion for Evaluation of Complex Structures

BackgroundValidation of models using full-field experimental techniques traditionally rely on local data comparisons. At present, typically selected data fields are used such as local maxima or selected line plots. Here a new approach is proposed called full-field data fusion (FFDF) that utilises the entire image, ensuring the fidelity of the techniques are fully exploited. FFDF has the potential to provide a direct means of assessing design modifications and material choices.ObjectiveA FFDF methodology is defined that has the ability to combine data from a variety of experimental and numerical sources to enable quantitative comparisons and validations as well as create new parameters to assess material and structural performance. A section of a wind turbine blade (WTB) substructure of complex composite construction is used as a demonstrator for the methodology.MethodsThe experimental data are obtained using the full-field experimental techniques of Digital Image Correlation (DIC) and Thermoelastic Stress Analysis (TSA), which are then fused with each other, and with predictions made using Finite Element Analysis (FEA). In addition, the FFDF method enables a new high-fidelity validation technique for FEA utilising a precise full-field point by point similarity assessment with the experimental data, based on the fused data sets and metrics.ResultsIt is shown that inaccuracies introduced because of estimation of comparable locations in the data sets are eliminated, The FFDF also enables inaccuracies in the experimental data to be mutually assessed at the same scale regardless of differences in camera sensors. For example, the effect of processing parameters in DIC such as subset size and strain window can be assessed through similarity assessment with the TSA.ConclusionsThe FFDF methodology offers a means for comparing different design configurations and material choices for complex composite substructures, as well as quantitative validation of numerical models, which may ultimately reduce dependence on expensive and time-consuming full-scale tests.

Обзор методов прогноза гидравлического разрыва противофильтрационного ядра каменно-земляной плотины

Introduction. The phenomenon of hydraulic fracture is associated with the failure of some earth-rock dams, in which the integrity of the core made of clay soil has been compromised. It is believed that hydraulic fracture occurs when the pressure of water contained in pores and microcracks overcomes the compressive stresses in the soil. At this point, several methods have been proposed for the computational prediction of hydraulic fracture. They are aimed at determining the conditions under which hydraulic fracture occurs and at determining the critical water pressure that causes fracture growth. Materials and methods. A review of foreign scientific publications was carried out to systematise information on methods and techniques for critical pressure determination. Results. The review gives a classification of methods for predicting hydraulic fracture. Theoretical methods are based on the usage of elasticity theory, plasticity theory or fracture mechanics. The simplest method is based on the analysis of the stress state of the soil mass. This review describes methods based on the analysis of the stress-strain state of soil around a cavity with internal pressure. They consider several mechanisms of crack propagation, including the loss of tensile and shear strength. Empirical formulas based on the results of laboratory experiments are also given. In the framework of the analytical review, a comparison of some methodologies has been carried out. Most of the methodologies agree that the critical pressure primarily depends on the minimum principal stress σ3 in the ground. The comparison showed that the critical pressure calculated by the theoretical triaxial stress analysis technique is noticeably lower than that calculated by the empirical techniques. In the presence of a cavity, the more likely cause of fracturing is the loss of shear strength of the soil rather than tensile strength. Conclusions. Despite the abundance of techniques for predicting hydraulic fracturing, no theoretically verified and accurate methodology has been established at the present time.

Evaluation of Pipeline Steel Mechanical Property Distribution Based on Multimicromagnetic NDT Method

To break through the drawbacks of traditional damage test methods that cannot obtain the full-plate mechanical property distribution of pipeline steel and are laboratory-dependent and costly, multimicromagnetic nondestructive testing (NDT) technology and machine learning technology are employed. The micromagnetic multiparameter microstructure and stress analysis (3MA) technique is used to extract 11 micromagnetic characteristics of pipeline steel. The Lorentz force-based electromagnetic ultrasound (EMAT) technique is applied to offset the defects of the 3MA technique in testing depth and extract ultrasonic velocity characteristics of pipeline steel as a new characteristic. Based on machine learning techniques, 12 characteristics are used for information fusion to evaluate the mechanical properties of the entire pipeline steel. The prediction results show that, compared with multilayer perceptron (MLP), random forest (RF), and deep neural networks (DNNs), the testing accuracy based on the extreme gradient boosting (XGBoost) algorithm was found to be the highest (PR10 over 93%). Meantime, based on the importance of parameters during the training of the XGBoost model, the modeling mechanism of the surface hardness and tensile strength models is investigated, providing a theoretical basis for analyzing the fusion of micromagnetic feature information based on machine learning (black box).

Physical and simulation modelling of solid media fracturing by means of explosive charges of different cross-sectional shapes

Purpose is to evaluate experimentally and theoretically a mechanism of solid media fracturing by means of explosive charges varying in their cross-sectional shapes. Methods. The Mohr-Coulomb strength condition has been applied to describe rock transition to the disturbed state. The condition has become a basis to develop a mathematical model of explosion (i.e. shock and detonation wave) of the concentrated borehole charges. The simulation explosion was modelled while adequate load applying at the points belonging to the outline of both cylindrical charge and at the charging angles in the shapes of triangular and square prisms. The evaluation mechanism of solid media fracturing by means of explosive charges, varying in their shapes, used the models made of optically active materials. A method of high-speed photorecording of the process was involved; the method was combined with the photoelastic technique of stress analysis. Findings. Taking into consideration rock transition to the disturbed state, the Mohr-Coulomb strength condition was applied with the possibility to simulate failures resulting from shear as well as from separation according to the developed mathematical model. The calculation results have helped identify distribution of a geomechanical parameter (Q) at different time points (time iterations). Dependencies of changes in the maximum component of the main stress tensor σ1 / γН along the axis passing through the charge centres perpendicularly to its flat surface for different time iterations have been developed. It has been defined that the maximal stresses are concentrated on the top of both triangular and square prisms helping shape a denser crack network within the zones. Originality. It has been identified that at the initial explosion stage, the maximum values of the main stress tensor component σ1 / γН along the axis passing through the charge centre perpendicularly to its flat surface, experience certain change depending upon a power law with the increasing distance to the charge outline. At the same time, if the charge is of a square prism shape then time iteration being i = 5 makes the main stress decrease according to a linear dependence. Practical implications. The research may be used as the basis for the development of rational parameters of the resource-saving methods applied to separate hard complex rocks in terms of open pits where building materials are mined.

Application of transmission photoelasticity in visualizing fluid-structure interactions

Photoelasticity is a stress analysis technique based on the principle that some materials act as waveplates when stressed. In this study, transmission photoelasticity is used as a novel optical technique to capture flow information. A bio-inspired structure is designed comprising a whisker-like shaft inserted into a sensing base made of photoelastic material. When the whisker-inspired structure encounters a flow stimulus, it deflects and generates a high bending stress in the sensing base that is transduced into a fringe pattern that correlates with the flow stimulus. The pattern is observed using a circular polariscope and is then linked to the flow stimulus encountered by the structure. The results show that this optical method can be employed to link a specific fringe pattern with the corresponding free stream velocity with a global accuracy of 85.7%. Also, this technique is able to detect an obstacle upstream of the bio-inspired structure. Transmission photoelasticity could help design flow sensing devices.

Stress analysis of total hip arthroplasty with a fully hydroxyapatite-coated stem: comparing thermoelastic stress analysis and CT-based finite element analysis

Purpose: The aim of this study was to evaluate the stress distribution in a synthetic femur that was implanted with a fully hydroxyapatite-coated stem using thermoelastic stress and finite element analyses, and to clarify the differences in the stress distributions between these two methods. Methods: Thermoelastic stress analysis is a stress-analysis technique that employs the thermoelastic effect. Sinusoidal vertical loads were applied to the head of the stem placed on the synthetic femur, and surface stress distribution images were acquired using an infrared stress measurement system. The finite element model for the synthetic femur and stem were set up similarly to the thermoelastic stress analysis experiment, and vertical load was applied to the head of the stem. Surface stress distribution and stress values obtained via these two methods were compared. Results: Thermoelastic stress analysis showed that compressive and tensile stresses were distributed from the proximal femur to the diaphysis, not only on the medial and lateral surfaces, but also on the anterior and posterior surfaces. However, finite element analysis showed that compressive stress was not distributed on the anterior and posterior surfaces of the femoral intertrochanter. The stress values of thermoelastic stress analysis tended to be higher in the proximal femur than that obtained via the finite element analysis. Conclusions: The surface stress distribution obtained by these two methods were different specifically in the proximal femur. Our results imply that thermoelastic stress analysis has a better potential than finite element analysis to show the surface stress distribution that reflects the stem design.

Effect of speckle size on surface crack detection via digital image correlation

Digital image correlation (DIC) is an experimental stress analysis technique used in nondestructive tests. The accuracy of DIC in crack detection depends on various factors such as the sizes of speckles and pixels. In the current study, a speckle pattern based on the spreading of nanoparticles with small speckles is compared with a conventional sprayed pattern to understand whether crack detection via DIC is improved by reducing the sizes of speckles and pixels. Owing to the small size of nanoparticles, an optical microscope is used for magnification. The spreading method for crack detection is first investigated experimentally. Results show that cracks can be detected easily when a 250 nm opening appears in the crack edges. Subsequently, the spreading method is compared with the conventional DIC, in which the spraying method is used for patterning, in terms of crack detection. Results show that by reducing the speckle size and closely analyzing the speckle pattern, the DIC technique is considerably better than the conventional technique in detecting small cracks. Moreover, the conventional method is more suitable for detecting large cracks.

Thermoelastic stress analysis as a method for the quantitative non-destructive evaluation of bonded CFRP T-joints

Adhesive bonding is a material joining process in which an adhesive, placed between the surfaces, solidifies to produce a strong bond. In this regard, adhesively bonded joints represent an interesting alternative to mechanical joints and provide many advantages over conventional mechanical fasteners: continuity of the structure, high strength-to-weight ratio, design flexibility, and easiness of fabrication.In the present research, the Thermoelastic Stress Analysis (TSA) technique has been used as a non-destructive tool for evaluating the mechanical behaviour of aeronautical adhesive bonded CFRP T-joints made by automated fibre placement process. Moreover, the thermoelastic signal was used for determining the debonded areas after the pull-off tests. The results in terms of the measured debonded area were compared to the well-established lock-in thermography technique. The capability of the Thermoelastic Stress Analysis to perform an in-depth study of the quality of T-joints has been demonstrated.

Similar biomechanical properties of four tripled tendon graft models for ACL reconstruction

PurposeThe present study tested and compared the biomechanical properties of four different triplicate graft tendon techniques.Methods32 tripled tendons from the common extensor muscle of bovine fingers were tested on a material testing machine, passing the end loop over a metal rod of a clevis connected to the load cell on the upper side, and fixing the lower end to a clamp. The samples were divided into four groups: (A) tripled with a free end sutured only to one of the two fixed bundles (B) tripled with a free end positioned between the two fixed strands and sutured to both (C) tripled with an S-shape and all the three strands sutured together at the upper and lower extremities of the graft (D) partially quadrupled with the free end sutured together with the other three bundles at the upper extremity. Each sample was pretensioned at 50 N for 10 min and then subjected to 1000 load control cycles between 50 and 250 N. Finally, each sample was subjected to a load to failure test.Authors also present some preliminary results on the feasibility of a non-contact and full-field Thermoelastic Stress Analysis technique, based on Infrared Thermography, to evaluate the level of stress on the whole graft, and hence on each strand, during fatigue loading.ResultsEighty five percent of the samples failed at the level of the clamp. The cyclical elongation progressively decreased in all the samples and there was a simultaneous increase in stiffness. An increased stiffness was noted between Group 2 vs Group 3 and Group 2 vs Group 4 at the 500th and 1000th cycle. The failure loads were as follows: (a) 569.10 N, (b) 632.28 N, (c) 571.68 N, (d) 616.95 N. None of the parameters showed a statistically significant difference between the four groups.ConclusionThis study reported similar biomechanical behavior of four different models of tripled grafts suitable for ACL reconstruction. In addition, the biomechanics of overall tripled tendon grafts seems more affected by the viscoelastic property of the tendon itself rather than the preparation method.

Origin and Application of the Twinned Calcite Strain Gauge

This paper is a personal account of the origin and development of the twinned-calcite strain gauge, its experimental verification, and its relationship to stress analysis. The method allows the calculation of the three-dimensional deviatoric strain tensor based on five or more twin sets. A minimum of about 25 twin sets should provide a reasonably accurate result for the magnitude and orientation of the strain tensor. The opposite-signed strain axis orientation is the most accurately located. Where one strain axis is appreciably different from the other two, that axis is generally within about 10° of the correct value. Experiments confirm a magnitude accuracy of 1% strain over the range of 1–12% axial shortening and that samples with more than 40% negative expected values imply multiple or rotational deformations. If two deformations are at a high angle to one another, the strain calculated from the positive and negative expected values separately provides a good estimate of both deformations. Most stress analysis techniques do not provide useful magnitudes, although most provide a good estimate of the principal strain axis directions. Stress analysis based on the number of twin sets per grain provides a better than order-of-magnitude approximation to the differential stress magnitude in a constant strain rate experiment.

Residual stress and fracture toughness of sintered body of ZrO2-GO composite ceramics material

Zirconia ceramics and carbon-based materials are widely adopted in medical and dental applications due to their excellent biocompatibility and aesthetics. However, fracture toughness of ceramic materials limits their application in clinical dentistry because of the existence of residual stress. In this study, zirconia/graphene oxide (ZrO2-GO) composite ceramics were fabricated by hot-press sintering. Residual stresses developed on the surface of ZrO2-GO composite ceramics were evaluated by X-ray residual stress analysis and indentation techniques. The variation of surface residual stress with GO content was evaluated, and found to be consistent with that of fracture toughness. The generation of residual stress was found to be directly related to fracture toughness. Residual stress calculated by theoretical formula of indentation method was consistent with that measured by X-ray diffraction in line with the content of GO. Based on above results, it is concluded that 0.1–0.15 wt% GO composite ceramics possessed better mechanical properties.

Analysis of the Stress Distribution Pattern of Anatomic and Non-Anatomic Tooth Forms on Maxillary and Mandibular Edentulous Ridges—A Photoelastic Study

Aim: To compare the type of stress distribution pattern occurring with anatomic and non-anatomic tooth forms beneath a complete denture in both maxillary and mandibular arch. Methodology: A photoelastic model of the edentulous maxillary and mandibular ridge was prepared meticulously to simulate the human mandible and maxilla. Two sets of acrylic teeth with anatomic and non-anatomic occlusal forms were used to fabricate upper and lower dentures. A vertical static load of 100 N was applied through the mandibular model to the maxillary model. After load application on the dentures the photoelastic model as well as the upper and lower complete dentures were sectioned in the midline. The sectioned photoelastic model was viewed through a polariscope to observe the fringe pattern indicating varying amounts of stress distribution. In this study, a two-dimensional photoelastic stress analysis technique was utilized. Results: Force per unit area was observed more in anatomic teeth than the non-anatomic counterpart. Hence anatomic tooth forms may increase the possibility of bone resorption rate over a period of time. However, in non-anatomic lower teeth, a decrease in value was observed from posterior to anterior region. Conclusion: Stress of greater magnitude was observed with cuspal teeth whereas non-anatomic (0°) showed slightly less magnitude of stress. Depending upon the clinical situation the clinician needs to choose the type of occlusal tooth forms for edentulous patients.

Coupled heat equation in thermoelasticity with temperature dependent moduli

New and consistent expressions for the coupled heat equation are developed within the framework of small-strain thermoelasticity for both Fourier and Cattaneo–Vernotte conduction models. These expressions place no restrictions on the changes in temperature, allow for the temperature dependence of the thermoelastic moduli, and include all the coupling terms as functions of the thermoelastic moduli and their derivatives. As applications, (i) an extended Lord–Shulman-type model is derived that takes into account the temperature dependence of the thermoelastic moduli, and (ii) the equations underpinning the experimental technique of thermoelastic stress analysis are revisited.

Investigations into the interface failure of yttria partially stabilised zirconia - porcelain dental prostheses through microscale residual stress and phase quantification

ObjectivesYttria Partially Stabilised Zirconia (YPSZ) is a high strength ceramic which has become widely used in porcelain veneered dental copings due to its exceptional toughness. Within these components the residual stress and crystallographic phase of YPSZ close to the interface are highly influential in the primary failure mode; near interface porcelain chipping. In order to improve present understanding of this behaviour, characterisation of these parameters is needed at an improved spatial resolution. MethodsIn this study transmission micro-focus X-ray Diffraction, Raman spectroscopy, and focused ion beam milling residual stress analysis techniques have, for the first time, been used to quantify and cross-validate the microscale spatial variation of phase and residual stress of YPSZ in a prosthesis cross-section. ResultsThe results of all techniques were found to be comparable and complementary. Monoclinic YPSZ was observed within the first 10μm of the YPSZ-porcelain interface with a maximum volume fraction of 60%. Tensile stresses were observed within the first 150 μm of the interface with a maximum value of ≈300 MPa at 50 μm from the interface. The remainder of the coping was in mild compression at ≈−30MPa, with shear stresses of a similar magnitude also being induced by the YPSZ phase transformation. SignificanceThe analysis indicates that the interaction between phase transformation, residual stress and porcelain creep at YPSZ-porcelain interface results in a localised porcelain fracture toughness reduction. This explains the increased propensity of failure at this location, and can be used as a basis for improving prosthesis design.

Development of a GPGPU‐parallelized hybrid finite‐discrete element method for modeling rock fracture

SummaryThe hybrid finite‐discrete element method (FDEM) is widely used for engineering applications, which, however, is computationally expensive and needs further development, especially when rock fracture process is modeled. This study aims to further develop a sequential hybrid FDEM code formerly proposed by the authors and parallelize it using compute unified device architecture (CUDA) C/C++ on the basis of a general‐purpose graphics processing unit (GPGPU) for rock engineering applications. Because the contact detection algorithm in the sequential code is not suitable for GPGPU parallelization, a different contact detection algorithm is implemented in the GPGPU‐parallelized hybrid FDEM. Moreover, a number of new features are implemented in the hybrid FDEM code, including the local damping technique for efficient geostatic stress analysis, contact damping, contact friction, and the absorbing boundary. Then, a number of simulations with both quasi‐static and dynamic loading conditions are conducted using the GPGPU‐parallelized hybrid FDEM, and the obtained results are compared both quantitatively and qualitatively with those from either theoretical analysis or the literature to calibrate the implementations. Finally, the speed‐up performance of the hybrid FDEM is discussed in terms of its performance on various GPGPU accelerators and a comparison with the sequential code, which reveals that the GPGPU‐parallelized hybrid FDEM can run more than 128 times faster than the sequential code if it is run on appropriate GPGPU accelerators, such as the Quadro GP100. It is concluded that the GPGPU‐parallelized hybrid FDEM developed in this study is a valuable and powerful numerical tool for rock engineering applications.

Evaluation of strain distribution on an edentulous mandible generated by cobalt-chromium metal alloy fixed complete dentures fabricated with different techniques: An in vitro study

Statement of problemFixed complete dentures (FCDs) have been used in the treatment of completely edentulous patients for over 40 years. However, few reports have investigated misfit values and strain distribution in the context of FCDs fabricated with new technologies. PurposeThe purpose of this in vitro study was to evaluate misfit values and strain distribution in FCDs and their relation to the fabrication technique of the cobalt-chromium (Co-Cr) metal framework. Material and methodsFour implants were placed in the interforaminal region of a mandibular cast at the bone level. The Co-Cr metal alloy frameworks were fabricated using the following techniques: computer-aided design and computer-aided manufacturing (CAD-CAM), milling from hard blocks, CAD-CAM milling from soft blocks, and direct metal laser sintering (DMLS). The superstructures of equal sizes with acrylic resin bases and acrylic resin denture teeth were fabricated on the Co-Cr metal alloy framework, and a digital microscope was then used to measure the misfit between the abutments and the implants. The stress formed after the application of torque was measured with a strain-gauge stress analysis technique. Data were statistically analyzed using 1-way ANOVA and the Tukey Honestly Significant Difference test (α=.05). The correlation between the misfit and the strain values was evaluated with the Pearson Correlation test (α=.001). ResultsThe lowest mean misfit values (99 ±17 μm) were observed in the hard block group (P<.05) and the highest in the DMLS group (139 ±29 μm). A statistically significant positive relationship was found between the misfit and the stress distribution after torque application (P<.05). Moreover, the lowest misfit group, hard blocks, had the lowest mean strain values (81.1 ±54 MPa) after torque application. ConclusionsWithin the limitations of this in vitro study, the fabrication technique used for Co-Cr metal alloy frameworks appears to influence the passive fit significantly (P<.05). The hard-block technique was found to be the most precise fabrication technique for Co-Cr metal alloy frameworks. A significant relationship was observed between the amount/distribution of misfit and the strain on the FCD (P<.05).

Pipeline Stress Analysis Through Stress Function Fittings

Abstract This work presents a hybrid experimental technique for stress analysis in pipes due to soil-pipe interaction. It was used a variation of Digital Speckle Pattern Interferometry (DSPI) combined with a small indentation setup for acquiring radial displacement points. Data collected are fitted under the Airy stress functions method for the determination of displacements and strain components. The radial displacement data is fitted in to extract Airy stress function coefficients in a short combination selected specifically for the analysis of stress fields in pipes. This technique is of great utility as an auxiliary approach to the actual field data compilation.

Thermal Stress Analysis of Residual Stress in a Cylindrical Aluminum Casting with Cast-in GCI Liner, Taking Recovery Behavior Effect into Account

Most aluminum cylinder blocks produced using high-pressure or low-pressure die-casting processes require gray cast iron liners (GCI liners) to compensate for their insufficient wear resistance and heat resistance of the Al-Si-Cu alloys. However, the cast-in liners cause excessive residual stress at the cylinder bore region. The resultant residual stress induces distortion of the cylinder liner. These inconveniences hinder development of more efficient engines. Therefore, an accurate thermal stress analysis technique has been sought to predict the residual stress and distortion of the cylinder liner. For accurate thermal stress analysis, we have already developed an elastoplastic-creep constitutive equation for which the inelastic strain developed at high temperatures does not contribute to strain hardening that occurs at low temperatures by duplicating the recovery behavior. Our earlier investigation using this equation has already revealed that incorporation of the recovery in the alloy constitutive equation is effective for improving the prediction accuracy of the thermal stress developed during casting. However, this conclusion was obtained only for a simple shape casting with a uniaxial thermal stress state. Effects of the developed constitutive equation have not been discussed for a casting closer to an actual cylinder block. For this study, a cylindrical aluminum casting with GCI (ISO 300) insert was produced. Then, the circumferential strain of the GCI liner was measured in-situ during casting. Measurements were taken of the residual stresses of the cylindrical aluminum casting and GCI liner, and of the liner deformation at a room temperature. The experimentally obtained results supported a discussion of the predictive accuracies of the elastoplastic-creep constitutive equation and the classical elastoplastic constitutive equation. A comparison revealed that the elastoplastic-creep constitutive equation for the aluminum casting has better predictive accuracy than the classical elastoplastic equation for residual stress, liner deformation, and the circumferential strain of a GCI liner during casting. Investigation of the simulated strain components of the cylindrical aluminum casting during casting indicated incorporation of the recovery in the alloy constitutive equation as a main factor improving the predictive accuracy.