Experimental Displacement Data Research Articles

A Methodology to Assess Directional and Spatial Variations of Tensile and Fracture Properties in Fabricated Nuclear Components

In the present study, directional and spatial variations in the mechanical properties are calculated in two nuclear-grade materials. In practice, multiple ASTM standard specimens are tested to measure mechanical properties of any material. The variations obtained in the properties during the tests are generally neglected assuming such variations are due to experimental uncertainties. However, such variations may indicate some degree of anisotropy and spatial inhomogeneity in the material due to component fabrication. In the present study, multiple miniaturized tensile specimens are tested. These specimen materials are taken across the thickness and at different geometrical locations in the two manufactured nuclear-grade components. The experimental load versus displacement data of all the specimens are then used to evaluate stress-strain data and cohesive zone parameters. These parameters are determined for each tested specimen separately to gather variations over the geometries of the components. Subsequently, TPB specimens are analyzed employing these parameters to calculate variations in fracture initiation toughness over the geometry. The key findings of the present work include higher strengths in circumferential direction in comparison to the longitudinal direction for SA333 Gr6 steel. A new equation is developed to correlate the material toughness with the fracture toughness with a proportionality constant of 2.7778 for low-alloy carbon steels. The study showed that directional and spatial variations in Jini are less pronounced in 20MnMoNi55 compared to SA333Gr6 materials. This finding is crucial for safety analyses in nuclear components and indicates that this methodology can be applied more widely across different materials.

Experimental and theoretical investigation of aortic wall tissue in tensile tests.

Understanding the mechanical properties of aortic tissue is essential for developing numerical computation tools and assessing the risk of aortic aneurysm fractures. Tensile tests using aortic wall specimens allow for the determination of stress and strain depending on the location and direction of the sample. The aim of this study was to perform a mechanical tensile test using canine aorta samples and create a numerical model of aortic tissue tension from the processed data. Dogbone-shaped samples were dissected from canine aortic segments. The initial measurements were made at zero tension and the tensile tests were conducted at 10 mm/min until rupture. Force and stretch data were used to obtain engineering and true stress-strain curves. The true stress-strain curves were taken until the maximum strength was obtained, after which they were smoothed and fitted using a logistic function with three coefficients. These curves were then used as material mechanical properties for a numerical model of the aortic tissue tension. A simplified rectangle form was used to mimic the middle of the dogbone-shaped portion of the tissue specimen. Experimental displacement data were collected for the boundary conditions of the finite element 3D model. The experimental data processing revealed that the logistic function described the nonlinear behaviour of the aorta soft tissue with an accuracy of 95% from the start of the tension to the media layer rupture. By applying numerical simulations, we obtained a correspondence of the load curve with an RMSE = 0.069 for the theoretical and experimental external tension data. The numerical investigation confirmed that the non-linear soft tissue was validated by applying a logistic function approach to the mechanical properties of the aortic wall.

Determination of mixed-mode I/II fracture toughness and bridging law of composite laminates

Accurate determination of the fracture toughness and the bridging law in a simple way is meaningful for the composite structural design. This study proposes a semi-analytical approach to calculate the mixed-mode I/II fracture toughness, and the crack opening/sliding displacements. Based on the relation between them, the mixed-mode I/II bridging law is obtained by using the J-integral theory. The obtained fracture toughness and distribution of the bridging stress show good agreements with test results, which illustrates the applicability of the semi-analytical approach. The obtained bridging law is further integrated into a tri-linear cohesive zone model for simulating the delamination behavior. Numerical load–displacement responses are consistent with experimental ones, further verifying the semi-analytical approach. Only experimental load and displacement data are necessary in this semi-analytical approach while specific equipment and tedious measurements on the delamination length and the relative crack opening/sliding displacement during the delamination tests are avoided, which makes the proposed approach simple and applicable for engineering application.

Strain Field Evolution Analysis of Brittle Shale with Initial Fractures Based on DIC

Wellbore instability mainly occurs in shale formations, and it is of great significance to deeply analyze the characteristics of shale-failure behavior to evaluate the stability of the shale surrounding the well wall during drilling. Through a uniaxial compression experiment and DIC technology, the whole strain field of shale specimens with prefabricated holes and cracks under uniaxial compression is measured. The experimental data of load, displacement and strain field are analyzed comprehensively. The results show that the fracture location and expansion path of shale are closely related to the evolution of the strain field. The evolution of the strain field directly affects the failure behavior of the rock. Under the action of load, local high strain will first appear around the initial shale defects (pores and fractures), and stress concentration will occur. With the increase of load, cracks and failures will first appear in the local high-strain zone, and the failure will spread along the region and path and eventually lead to the overall failure of the rock. The establishment of a description method for shale-failure behavior through strain-field evolution can effectively analyze the crack behavior of shale with initial defects such as holes and cracks and provide theoretical and experimental bases for the stability evaluation of the shale surrounding the well wall, including shale-strength prediction and shale-failure mechanism.

Numerical identification of position-dependent friction coefficients from measured displacement data in a bolt-nut connection

Friction is a complex system affected by microscopical effects and multidisciplinary phenomena. Coulomb's simple friction model with a constant friction coefficient cannot account for all these tribological effects. Nevertheless, this model is still widely utilised for calculations of mechanical applications. In order to reflect the importance of friction as a parameter for functionality, we need more realistic and sophisticated calculations. This is particularly relevant for bolt-nut connections, which serve as motivating example for our study. Our approach is to introduce position-dependent friction coefficients by dividing the contact surface into different friction areas, each characterised by a constant friction coefficient. These coefficients are then adapted to measured displacement data. To this end, we develop a numerical parameter identification tool. The tool combines calculations in Ansys Mechanical, an established Finite Element software, and Microsoft's Visual Basics for Applications for optimisation purposes. We verify the parameter identification tool using the simple model of a block on a planar surface. Within this test scenario, the algorithm converges and provides a good approximation of the friction coefficients. Subsequently, we apply parameter identification to the model of a bolt-nut connection. We perform optical measurements to acquire experimental displacement data. The parameter identification tool demonstrates its functionality. Finally, we discuss future modifications of the procedure, that will enable more realistic and reliable results.

Prediction of nanoindentation creep behavior of tungsten-containing high entropy alloys using artificial neural network trained with Levenberg–Marquardt algorithm

This paper describes the synthesis of tungsten-containing high-entropy alloys (HEAs). The synthesis method involves a powder metallurgy process, and spark plasma sintering (SPS) is used to compact the powder. XRD and SEM analyses of synthesized HEAs showed that the main phases formed were body-centered and face-centered cubic phases, and a sigma phase was also observed after sintering at 900 ℃. Furthermore, nanoindentation showed that the introduction of tungsten in HEA resulted in high hardness and elastic modulus, which ranged from 8.31 to 13.57 GPa and 197.21–209.43 GPa respectively. The indentation creep behavior was ascertained at room temperature. The HEAs exhibited a significant benchmark after the addition of a specific amount of W for further investigation because of their lower creep rate. Experimental creep displacement data were used for modeling by artificial neural networks (ANNs) in which the training has been performed by the Levenberg–Marquardt algorithm. The experimental creep displacement data and the ANN model predictions have an excellent agreement. The ANN model is reliable and can accurately forecast the room temperature creep behavior of HEAs. HEAs are promising candidates for use in elevated and wear-resistance applications, owing to their unique combination of high hardness and high creep resistance.

Simulation analysis model of high-speed motorized spindle structure based on thermal load optimization

High-end CNC machine tools' primary transmission mechanism is a high-speed electric spindle. Thermal displacement of the spindle occurs as a result of heat created inside the spindle during transmission, which has an impact on the machining precision of high-end CNC machine tools. Establishing a high-precision motorized spindle simulation model is crucial because it serves as a foundation for optimizing and testing the motorized spindle's construction and material, adjusting for thermal errors, and estimating its life. The thermal-solid coupling model of the motorized spindle is created by Ansys based on the experimental data of temperature and thermal displacement of the A02 motorized spindle and in accordance with the boundary conditions. The accuracy of front and rear bearings is 93.42% and 90.52%, respectively, when compared to experimental data, and the accuracy of axial thermal displacement is 95.16%. Finally, the motorized spindle is optimized to extend its service life after the thermal displacement, stress, and strain of the bearing are model.

Numerical identification of the elasticity tensor of heterogeneous materials made of Silicon Carbide and Titanium by the Finite Element Model Updating (FEMU)

This work is subjected to the development of a method to identify the elasticity tensor of homogeneous and heterogeneous materials. The materials are created in the form of checkerboards. We solved the direct problem to obtain the strain field using the finite element method, after obtaining this strain field, we created synthetic experimental displacement data by simulation. A re-calibration of the created experimental and simulated data is done based on the principle of the finite element model updating (FEMU), used in almost all domains, in the inverse problem. The minimization of the cost function obtained by FEMU is done by Levenberg-Marquardt algorithm which is very fast and elegant algorithm. A complete study has been done by studying the sensitivity of the identified values with respect to the refinement of the mesh and with respect to the level of disturbance.

Measuring unsteady drag of the flow around a sphere based on time series displacement measurements using physics-informed neural networks

Surface drag increases energy usage and emissions in numerous transport and engineering applications, with surface treatment being one technique aimed at reducing surface skin friction and hence, surface drag. One approach to investigate the performance of surface treatments is based on the measurement of the terminal velocities of settling spheres with and without surface treatment. This relatively affordable method is limited to the terminal velocity region, as the analysis of the data during the accelerating phase of the sphere requires the differentiation of the experimental data, which results in significant noise and drag measurements with high uncertainty. This paper compares two neural network approaches to determine the temporal derivatives of experimental data. Specifically, the ensemble averaged experimental data and physics information is used to define a model for a settling sphere, which is used to test the performance of neural networks trained on noisy displacement data using an approach based on the governing differential equation and a direct approach, with varying loss term weights, measurement error levels and temporal resolutions. The results show that the neural network trained directly on the experimental displacement data is able to reduce the uncertainty of the temporal derivatives to a level similar to that of the differential equation approach when initial conditions are included in the training. Finally, the two approaches are applied to experimental data to determine the unsteady drag. This paper demonstrates that neural networks can be used to determine the temporal derivatives of experimental data with relatively low uncertainty, particularly where the system physics is at least partially known.

Deviation-based calibration for progressive damage analysis in pultruded glass fiber reinforced composites

This paper presents a systemic calibration methodology to efficiently simulate progressive damage evolution in four different pultruded glass fiber reinforced polymer (GFRP) composites using the strain-based COMposite DAMage Model (CODAM2) in the commercial finite element software LS-DYNA. In particular, Compact Tension (CT), scaled-up CT, and wide CT tests are simulated to find the best set of input parameters by considering four distinct indicators obtained from experimental and numerical load vs displacement data. By combining these indicators into a physically meaningful equivalent deviation value via a linear weighted-sum method, the results show that the most suited input damage variables yield physically accurate crack length predictions which underlines the robustness and accuracy of the proposed method. Furthermore, it is shown that the incorporation of bi-linear softening laws improves CODAM2 simulation results by up to 90%, however it also increases the number of parameters to be calibrated.

A semi-analytical method for determining mode-II fracture toughness and bridging law of composite laminates

Accurate determinations of fracture toughness and the bridging law are important for the design and analysis of composite laminates. In this work, based on the Castigliano theorem and the point friction theory, a semi-analytical method for mode-II fracture toughness and bridging law is established. ENF tests on T800 carbon/epoxy laminates are carried out and fracture toughness are obtained. Public data from laminates made by other different materials are also used for verification. It is found the fracture toughness calculated by the semi-analytical method agree well with experimental results, verifying the accuracy of the proposed method for determining fracture toughness. Furthermore, the relative shear displacement at the pre-crack tip is also calculated and its relation with fracture toughness is established, from which bridging law can be determined by J-integral theory. The determined bridging law is integrated into cohesive zone model for delamination growth modelling. Good agreements between numerical and experimental load–displacement curves exhibit, which further verifies the proposed method. Using the proposed method, only experimental load and displacement data are required when determining fracture toughness and bridging law. Problems of unstable crack growth and difficult observation due to the compression of delamination are avoided in a simple and efficient way.

Initial cyclic hardening behavior of cracked structures under large-amplitude cyclic loading

A new cyclic hardening model is proposed based on combined experimental and numerical analyses to simulate the deformation of a cracked structure under large amplitude cyclic loading. In the experiment conducted herein, compact tension specimen tests made of TP304 stainless steel were subjected to large-amplitude cyclic loading. Then, finite element (FE) analysis was performed using the ABAQUS debond option to develop a cyclic hardening model. In the proposed cyclic hardening law, isotropic hardening was calculated in the first loading cycle. To assess the unloading of the first cycle, a Chaboche combined hardening model was used. The model results agreed well with the experimental displacement data. The effects of hardening in the first loading cycle on the yield surface and equivalent plastic strains in the subsequent cycles are presented as well.

Transient modelling of impact driven needle-free injectors

Needle-free jet injectors (NFJIs) are one of the alternatives to hypodermic needles for transdermal drug delivery. These devices use a high-velocity jet stream to puncture the skin and deposit drugs in subcutaneous tissue. NFJIs typically exhibit two phases of jet injection – namely – an initial peak-pressure phase (< 5 ms), followed by a constant jet speed injection phase (≳ 5 ms). In NFJIs, jet velocity and jet diameter are tailored to achieve the required penetration depth for a particular target tissue (e.g., intradermal, intramuscular, etc.). Jet diameter and jet velocity, together with the injectant volume, guide the design of the NFJI cartridge and thus the required driving pressure. For device manufacturers, it is important to rapidly and accurately estimate the cartridge pressure and jet velocities to ensure devices can achieve the correct operational conditions and reach the target tissue. And thus, we seek to understand how cartridge design and fluid properties affect the jet velocity and pressure profiles in this process. Starting with experimental plunger displacement data, transient numerical simulations were performed to study the jet velocity profile and stagnation pressure profile. We observe that fluid viscosity and cartridge-plunger friction are the two most important considerations in tailoring the cartridge geometry to achieve a given jet velocity. Using empirical correlations for the pressure loss for a given cartridge geometry, we extend the applicability of an existing mathematical approach to accurately predict the jet hydrodynamics. By studying a range of cartridge geometries such as asymmetric sigmoid contractions, we see that the power of actuation sources and nozzle geometry can be tailored to deliver drugs with different fluid viscosities to the intradermal region.

Calibration of a Heterogeneous Brain Model Using a Subject-Specific Inverse Finite Element Approach.

Central to the investigation of the biomechanics of traumatic brain injury (TBI) and the assessment of injury risk from head impact are finite element (FE) models of the human brain. However, many existing FE human brain models have been developed with simplified representations of the parenchyma, which may limit their applicability as an injury prediction tool. Recent advances in neuroimaging techniques and brain biomechanics provide new and necessary experimental data that can improve the biofidelity of FE brain models. In this study, the CAB-20MSym template model was developed, calibrated, and extensively verified. To implement material heterogeneity, a magnetic resonance elastography (MRE) template image was leveraged to define the relative stiffness gradient of the brain model. A multi-stage inverse FE (iFE) approach was used to calibrate the material parameters that defined the underlying non-linear deviatoric response by minimizing the error between model-predicted brain displacements and experimental displacement data. This process involved calibrating the infinitesimal shear modulus of the material using low-severity, low-deformation impact cases and the material non-linearity using high-severity, high-deformation cases from a dataset of in situ brain displacements obtained from cadaveric specimens. To minimize the geometric discrepancy between the FE models used in the iFE calibration and the cadaveric specimens from which the experimental data were obtained, subject-specific models of these cadaveric brain specimens were developed and used in the calibration process. Finally, the calibrated material parameters were extensively verified using independent brain displacement data from 33 rotational head impacts, spanning multiple loading directions (sagittal, coronal, axial), magnitudes (20–40 rad/s), durations (30–60 ms), and severity. Overall, the heterogeneous CAB-20MSym template model demonstrated good biofidelity with a mean overall CORA score of 0.63 ± 0.06 when compared to in situ brain displacement data. Strains predicted by the calibrated model under non-injurious rotational impacts in human volunteers (N = 6) also demonstrated similar biofidelity compared to in vivo measurements obtained from tagged magnetic resonance imaging studies. In addition to serving as an anatomically accurate model for further investigations of TBI biomechanics, the MRE-based framework for implementing material heterogeneity could serve as a foundation for incorporating subject-specific material properties in future models.

A Robust Finite Element-based Filter for Digital Image and Volume Correlation Displacement Data

Digital Image and Volume Correlation (DIC and DVC) are non-contact measurement techniques that are used during mechanical testing for quantitative mapping of full-field displacements. The relatively high noise floor of DIC and DVC, which is exasperated when differentiated to obtain strain fields, often requires some form of filtering. Techniques such as median filters or least-squares fitting perform poorly over high displacement gradients, such as the strain localisation near a crack tip, discontinuities across crack flanks or large pores. As such, filtering does not always effectively remove outliers in the displacement field. This work proposes a robust finite element-based filter that detects and replaces outliers in the displacement data using a finite element method-based approximation. A method is formulated for surface (2D and Stereo DIC) and volumetric (DVC) measurements. Its validity is demonstrated using analytical and experimental displacement data around cracks, obtained from surface and full volume measurements. It is shown that the displacement data can be filtered in such a way that outliers are identified and replaced. Moreover, data can be smoothed whilst maintaining the nature of the underlying displacement field such as steep displacement gradients or discontinuities. The method can be used as a post-processing tool for DIC and DVC data and will support the use of the finite element method as an experimental–numerical technique.

Mechanical characterization of fish oil microcapsules by a micromanipulation technique

This paper aims to study the mechanical properties of fish oil microcapsules made of different food-grade formulations and processing conditions, which is crucial to maintaining their mechanical integrity in further compaction for developing the final dosage form of tablet. The combination of gelatin and gum Arabic or maltodextrin were use as wall materials. Spray drying, complex coacervation, and double encapsulation (coacervation followed by spray coating) were used to prepare different fish oil microcapsules. Both fundamental physical properties and mechanical properties of microcapsules were investigated. The mechanical characterization results were obtained using a micromanipulation technique and revealed that the mean rupture forces of individual microcapsules ranged from 0.44 ± 0.11 to 1.73 ± 0.27 mN and tended to increase with increasing particle size. The Young's modulus of microcapsules was determined by fitting the experimental force versus displacement data with the Hertz model. The microcapsules prepared by coacervation of gelatin and gum Arabic followed by spray coating with a mixture of gelation and maltodextrin were the strongest and stiffest based on the calculated nominal rupture stress and Young's modulus respectively. These findings can provide guidance on choosing the most desirable formulation and processing conditions to produce strong microcapsules with desirable barrier properties for industrial applications.

Dynamic modelling and control of shear-mode rotational MR damper for mitigating hazard vibration of building structures

Magneto-rheological (MR) materials and their devices are being rapidly developed and have drawn surge of interest for the potential application in vibration control. Among them, a novel shear-mode rotational MR damper (SM-RMRD) with adaptive variable stiffness and damping was developed for adaptive structural control in real-time against different types of earthquakes. To make use of this innovative device perfectly, a robust and reliable model should be developed to simulate the nonlinear and hysteretic behaviours for the application in adaptive control. Accordingly, this research initially presents a new phenomenological model to describe the force response of the SM-RMRD. Then, model parameters are estimated based on experimental data of force, displacement and velocity, which were directly or indirectly obtained from the device under different loading protocols. The field dependence of each model parameter is also investigated so that a general model with current-related parameters is acquired for designing the control strategy. Using the current-dependent model of SM-RMRD, a semi-active controller is developed and implemented to the SM-RMRD to produce the feedback control for the structures in real-time. Finally, the effectiveness of proposed control method is appraised by a numerical study, in which an SM-RMRDs-incorporated three-storey building model with different control strategies are subjected to various scaled benchmark earthquakes. The comparison result verifies the excellent capacity of the proposed controller based on the developed phenomenological model in terms of reducing the storey acceleration and inter-storey drift.

Development of a computational model for acute ischemic stroke recanalization through cyclic aspiration.

Acute ischemic stroke (AIS), the result of embolic occlusion of a cerebral artery, is responsible for 87% of the 6.5 million stroke-related deaths each year. Despite improvements from first-generation thrombectomy devices for treating AIS, 80% of eligible stroke patients will either die or suffer a major disability. In order to maximize the number of patients with good outcomes, new AIS therapies need to be developed to achieve complete reperfusion on the first pass. One such therapy that has shown promise experimentally is the application of cyclic aspiration pressure, which led to higher recanalization rates at lower pressure magnitudes. In order to investigate AIS and cyclic aspiration recanalization, an improved computational modeling framework was developed, combining a viscoelastic thromboembolus model with a cohesive zone (CZ) model for the thromboembolus-artery interface. The model was first validated against experimental displacement data of a cyclically aspirated thromboembolus analog. The CZ model parameters, including the addition of a damage accumulation model, were then investigated computationally to determine their individual effects on the thromboembolus and CZ behavior. The relaxation time and the damage model critical opening length were shown to have the greatest effect on the CZ opening and led to increased displacement that accumulated with repeated loading. Additional simulations were performed with parameters relevant to AIS including internal carotid artery dimensions and thromboemboli mechanical properties. In these AIS cases, more upstream CZ opening was observed compared to the thromboembolus analog cases and greater displacement was achieved with the lower-frequency aspiration (0.5 vs 1Hz).

Slip perturbation during fault reactivation by a fluid injection

Slip orientation inferred from fault striae or focal mechanism datasets is commonly used in stress inversion methods based on the Wallace-Bott hypothesis. The hypothesis postulates that slip on a fault plane is collinear with the orientation of the resolved shear stress. It is valid for a single planar fault subjected to a homogeneous far-field stress. However, the experimental displacement data from an induced fault reactivation experiment, conducted in the Mont Terri rock laboratory, Switzerland, indicated multiple triggered slip orientations, thereby preventing application of the above inversion method. We present numerical and analytical results of slip on a reactivated fracture with a non-uniform fluid pressure distribution. Using these models, we evaluate the reasons for the inconsistency of our observations and the traditional Wallace-Bott hypothesis and test the physical effects of various parameters on fault slip. In the fully coupled hydromechanical numerical model (three-dimensional distinct element method), fluid pressure at a point on the fault surface is increased stepwise (assumed planar and singular) until shear reactivation of the fault is induced. We studied two different models with high and low fault plane stiffness to represent hard and soft rock masses, respectively. The model shows that high fault stiffness preserves the planarity of the fault plane, while low fault stiffness permits dilation and morphological changes of the fracture related to fluid pressure diffusion. The highest slip perturbation was observed in the low stiffness model due to the change of the fracture shape, controlled by the non-uniform pressure distribution. The Eshelby analytical solution confirmed that the more the fracture is dilated, the more the corresponding resolved shear stress is perturbed. Additionally, when compared to dilation and fault aperture, the friction angle has the most influence on the angular difference between geomechanical slip vectors and resolved shear stress.

Three-Dimensional Finite Element Simulations on Impact Responses of Gels With Fractional Derivative Models

Fractional derivative constitutive models, developed by the present authors (CND, vol.10, 061002, 2015), are implemented into a commercial finite element (FE) software, abaqus (referred to as a computational model) for solving dynamic problems of gel-like materials. This software is used to solve impact responses of gels, and the solutions are compared with the experimental results. The FE results reproduce well the experimental acceleration and displacement data from different types of gels whose properties are characterized by the fractional order and material parameters. Thus, the computational model presented here was validated. The fractional derivative model is compared with the Simo model (Computer Method in Applied Mechanics and Engineering, 60:153–173, 1987), which is an integer order derivative model. The response of the fractional derivative model can be approximated well when appropriate parameters of the Simo model are used. In the finite element method (FEM), compressibility is introduced artificially for simulations. Interpretations are given on the compressibility of materials in the FEM.