3D Digital Image Correlation System Research Articles

Experimental and numerical assessment of two reconstructive techniques for the fragility fractures of the pelvis type Ia.

Anterior pelvic ring fractures are common in geriatric patients. The Supraacetabular External Fixator (SEF) is a relatively simple and effective surgical procedure. On the other hand, there is the option of a Subcutaneous Iliopubic Plate (SIP) osteosynthesis. Only limited comparative biomechanical data of these two devices are available. Therefore, this biomechanical study's objective was to compare the stabilizing effect of the SEF versus the SIP in a model of Fragility Fractures of the Pelvis (FFP) type Ia. A test stand for pelvic biomechanics testing that emulates the gait loading cycle with physiological relevance was used. The osteotomy on the right pelvic ring was stabilized either with the SEF or the SIP. Strain gauges were used to measure strain in the pelvic ring. The osteotomy's spatial interfragmentary displacement (SID) was monitored using a 3D digital image correlation system. The SEF stabilization reduced the SID by approximately 10%, whereas the locking SIP could reduce displacement by about 62%. Additionally, the SIP reduced the stress/strain levels by 67% in the posterior pelvic ring. We could demonstrate that the SIP is superior to SEF in treating FFP type Ia as it significantly reduced the osteotomy's SID and the strain in the posterior pelvic ring.

Study on the bending and shear properties of quasi-honeycomb sandwich structures considering the variable-density core design

The quasi-honeycomb cell has better coplanar bearing capacity and stability in comparison with a honeycomb cell. The topology optimization can achieve the best distribution of materials within a core composed of cells. Hence, this paper makes an effort to provide a clear understanding about the enhancement effect of the core’s variable-density topology optimization on the mechanical properties of a quasi-honeycomb sandwich structure. The SR (i.e., the initials of SIMP and RAMP) interpolation function, obtained by weighting the Solid Isotropic Material with Penalization (SIMP) and Rational Approximation of Material Properties (RAMP) functions, is modified by adding the minimum elastic modulus term. The Optimal Classification (OC) algorithm is revised by adopting the volume constraint of Bi-directional Evolutionary Structural Optimization (BESO). And then taking into account the mapping between the topology elements and cells, the material distribution optimization of the quasi-honeycomb core is performed to minimize the structural compliance. The failure behavior, strength, stiffness, and energy absorption of three-dimensional (3D) printed uniform and variable-density quasi-honeycomb sandwich structures are studied by three-point bending tests, and the evolution processes and distribution laws on the displacement and strain of cores are analyzed using the 3D Digital Image Correlation (DIC) system. The comparisons between the experimental and numerical results are also carried out for the displacement and energy absorption of the sandwich structure, the bending strength of the face sheet, and the displacement and strain fields of the core. The results show that the bending strength, bending stiffness, shear strength, and energy absorption are enhanced after the variable-density topology optimization of the core, and the numerical values agree well with the experimental data. This study provides new ideas and important guidance for the variable-density design of quasi-honeycomb cores and the mechanical performance improvement of sandwich structures.

The Calibration Process and Setting of Image Brightness to Achieve Optimum Strain Measurement Accuracy Using Stereo-Camera Digital Image Correlation

Combining the drilling method with the digital image correlation (DIC) method is becoming more common to speed up the measurement and evaluate the strains relieved at several locations. However, to obtain the most accurate results, it is necessary to be aware of the influence of possible aspects that could adversely affect the results of the strain/stress analysis carried out using DIC. The paper describes several analyses to assess the influence of the 3D DIC system’s calibration procedure for strain/stress analysis of the specimen with a hole loaded with four different levels of tensile force. In addition, the paper also deals with the analysis of the influence of the image brightness, which was modified by changing the exposure time of the cameras. Based on the results of strain/stress analyses performed on small areas (approx. 25 × 25 mm) of a specimen with a hole by a stereo-camera DIC system, it can be concluded that both analysed factors can negatively influence the results. The most accurate results are ensured using the calibration target of very high manufacturing precision sized similarly to the field of view observed in correlation mode. The optimal image brightness is adjusted when the mean grey value of the image is from the range of 56 up to 171 with as evenly distributed image point intensities as possible.

Modal analysis of composite plates: Digital image correlation method application

Composite materials and structures are widely used and applied in many industries owing to their advantages, such as satisfactory stiffness-to-mass ratio and corrosion resistance. However, during their operating life, responsible parts subject to complex loads may change and their properties might deteriorate. To ensure structural integrity it is necessary to monitor and regularly check the performance of composite structures. This paper investigates the change of frequency characteristics of two rectangular composite (carbon-epoxy) plates after inflicting structural damage. Following the necessary preparation of the structure's upper surfaces by white-and-black stochastic pattern, the responses (free vibratory movement) of structures to momentary excitation were recorded by an optical, contactless 3D digital image correlation (DIC) system that contains a set of ultrafast cameras. In order to determine the natural frequencies of the plates, the recorded time-domain responses were post-processed, i.e. converted to the frequency domain by fast Fourier transform (FFT). The reduction in values of natural frequencies is observed on the damaged structures. The performed experiments demonstrate the applicability of the DIC method in the structural health monitoring of composite parts.

Study on the Compressive Properties of an Elastomeric Porous Cylinder Using 360° Three-Dimensional Digital Image Correlation System.

To study the compressive properties of an elastomeric porous cylinder, a 360° 3D digital image correlation (DIC) system is proposed. This compact vibration isolation table system captures different segments of the object from four different angles and fields of view, enabling a comprehensive measurement of the full surface of the object. To increase the stitching quality, a coarse-fine coordinate matching method is presented. First, a three-dimensional rigid body calibration auxiliary block is employed to track motion trajectory, which enables preliminary matching of four 3D DIC sub-systems. Subsequently, scattered speckle information characteristics guide fine matching. The accuracy of the 360° 3D DIC system is verified through a three-dimensional shape measurement conducted on a cylindrical shell, and the maximum relative error of the shell's diameter is 0.52%. A thorough investigation of the 3D compressive displacements and strains exerted on the full surface of an elastomeric porous cylinder are investigated. The results demonstrate the robustness of the proposed 360° measuring system on calculating images with voids and indicate a negative Poisson's ratio of periodically cylindrical porous structures.

Experimental investigation on the buckling and post-buckling behavior of variable stiffness laminates

On the basis of adequate considering the process constraints and defect control methods of tow curve placement, two types of variable stiffness laminates were designed and manufactured. A comprehensive experiment has been carried out through the 3D digital image correlation system, strain gauges, and displacement meters. The measured results show that the buckling and failure loads of variable stiffness specimens are improved by at least 40% and 70%, respectively. The FEA results of out-of-plane displacement and strain agree well with the experimental results. Furthermore, the reason for the higher buckling and failure loads of the variable stiffness specimens was elucidated by numerical results.

Ballistic resistance of high-strength armor steel against ogive-nosed projectile impact

The advanced high-strength armor steel with the superior strength-to-weight ratio can extremely improve the ballistic resistance and mobility of military equipment and structures. Aiming to assess the ballistic resistance including the ballistic limit and failure modes of two types of advanced high-strength armor steels, the projectile perforation test and numerical simulations were conducted. Firstly, ten shots of 15 mm-caliber ogive-nosed projectile perforation test were performed under the initial impact velocities of 164–428 m/s. The failure mode and out-of-plane displacement (OPD) response of target plate were recorded by utilizing the high-speed 3D digital image correlation system. Then, the classical finite element (FE) and mesh-free Smoothed Particle Galerkin (SPG) methods were adopted to conduct the numerical simulations, respectively. The predicted residual velocities of projectile were compared with the test data to verify the accuracy of the calibrated constitutive model parameters and numerical analysis approaches. By further comparing the failure modes and OPD–time histories of target, it was drawn that the FE method is preferable to reproduce the failure mode of target, while the SPG method is recommended to quickly predict the residual velocity of projectile. Finally, by adopting the validated numerical analysis approach, the residual velocities for two types of high-strength armor steels under the initial impact velocity range of 150–600 m/s were obtained. The reliabilities of the existing seven analytical models in predicting the ballistic limit and residual velocity for high-strength armor steels were further evaluated.

Experimental Investigation of Double-Sided Strain of Composites in Tensile Testing Using MultiCamera DIC

Composite materials are widely used in engineering because of their high strength, high modulus, and corrosion resistance. Accurately obtaining the mechanical properties of composites is helpful for their further development. However, in a uniaxial tensile test, the strain distribution between the front and back of the composite sheet sample may differ due to its heterogeneity, and its stress-strain curve depends on which side the strain is measured. To report the stress-strain curve more accurately, a multicamera digital image correlation (DIC) system was employed to measure the double-sided strain in this work. Two sets of 3D digital image correlation (3D-DIC) systems were placed in front of and behind the specimen to record the tensile process of the specimen, and a double-sided calibration technique was implemented to connect the two sets of 3D-DIC systems into a unified coordinate system. Young’s modulus, percent bending, and local strain history are analyzed based on the measurements of strain on both sides. The results show that the strain on both sides of the composite is not exactly same, especially in the strain concentration area. As a comparison, the strain distribution on both sides of the metal material is almost identical.

Digital image correlation-aided non-destructive buckling load prediction of cylindrical shells

The buckling capacity of a thin cylindrical shell depends on the unknown existed imperfections. Therefore, the prediction of the shell buckling load is still challenging if not impossible. In this paper, the prediction of critical buckling load of axially compressed cylindrical shell is investigated based on the novel non-destructive probing method. In order to find the proper locations for probing, we have combined the digital image correlation (DIC) technique with the non-destructive probing procedures. We have designed and built a 360° three-dimensional (3D) DIC system to reveal the displacement fields of the cylindrical shells and especially the commercial aluminum cans under axial compressions. Through the combination of experiments, numerical simulations and theoretical analysis, nonlinear force-indentation responses of the imperfect shells with non-zero local Gaussian curvatures to the point indentation were analyzed to guide the choice of the proper locations for the indentation. Our results demonstrate that the buckling load prediction of imperfect cylinders is possible if the probing is done sufficiently close to the dominating imperfection location, which could be detected and localized using the DIC technique.

The Radial Bulging and Axial Strains of Intervertebral Discs during Creep Obtained with the 3D-DIC System.

Creep-associated changes in disc bulging and axial strains are essential for the research and development of mechano-bionic biomaterials and have been assessed in various ways in ex vivo creep studies. Nonetheless, the reported methods for measurement were limited by location inaccuracy, a lack of synchronousness, and destructiveness. To this end, this study focuses on the accurate, synchronous, and noninvasive assessment of bugling and strains using the 3D digital image correlation (3D-DIC) system and the impact of creep on them. After a preload of 30 min, the porcine cervical discs were loaded with different loads for 4 h of creep. Axial strains and lateral bulging of three locations on the discs were synchronously measured. The three-parameter solid model and the newly proposed horizontal asymptote model were used to fit the acquired data. The results showed that the load application reduced disc strains by 6.39% under 300 N, 11.28% under 400 N, and 12.59% under 500 N. Meanwhile, the largest protrusion occurred in the middle of discs with a bugling of 1.50 mm, 1.67 mm, and 1.87 mm. Comparison of the peer results showed that the 3D-DIC system could be used in ex vivo biomechanical studies with reliability and had potential in the assessment of the mechanical behavior of novel biomaterials. The phenomenon of the largest middle protrusion enlightened further the strength of spinal implants in this area. The mathematical characterizations of bulging and strains under different loads yielded various model parameters, which are prerequisites for developing implanted biomaterials.

Blast Effects of a Shear Thickening Fluid-Based Stemming Material

The Trauzl test is widely used to measure the explosive power of a substance by determining the volume increase produced by the detonation of a tested explosive charge in the cavity of a lead block with defined quality and size. In this study, the Trauzl lead block test and a high-speed 3D digital image correlation (3D-DIC) system were used to evaluate the effect of stemming on a blast hole. The blasting experiments were conducted with emulsion explosives. The stemming materials adopted in this study were sand, aggregate, and shear thickening fluid (STF)-based stemming materials. The results of the blasting experiments and numerical analysis showed that the expansion rate of the lead block was most affected by STF-based materials, followed by aggregates and sand stemming. Furthermore, the displacement and surface strain on the block were the highest in the experimental case using STF-based stemming materials. The STF-based stemming material developed in this study in open pit mining or various blasting constructions is expected to increase rock fragment efficiency, compared to that of general blasting stemming methods, and reduce blasting vibration by decreasing the amount of explosive per blast hole used for blasting.

Wrinkling suppression in thin membranes using designed geometrical features

The rapidly increasing use of thin membranes; especially in the fabrication of flexible electronics, has motivated investigating the wrinkling behavior of these membranes. Wrinkling has an undesirable effect since wrinkles degrade the surface accuracy of structures incorporating thin membranes. This work introduces and evaluates an approach based on including optimized geometric features in thin membranes to suppress their wrinkling behavior. The ability of the optimized geometric features to suppress wrinkling in a 25 μm thick polyimide membrane subjected to uniaxial stretching is investigated computationally and experimentally in this work. A finite element model is developed to predict the wrinkling behavior of the membrane. An experimental setup equipped with 3D digital image correlation system is used to determine the wrinkles pattern, amplitude, and wavelength. Symmetric circular holes are introduced in the membrane to redistribute the stress field, eliminate the fluctuation in the minor principal stress in the membrane, and suppress wrinkles. The location and size of the circular holes are determined by coupling the Non-Linear Programming by Quadratic Largrangian technique and finite element simulations. An optimal design is obtained and the experimental results show that the optimally designed holes effectively suppressed the wrinkling behavior.

Reverse total shoulder arthroplasty baseplate stability with locking vs. non-locking peripheral screws

BackgroundThere are many options for glenosphere baseplate fixation commercially available, yet there is little biomechanical evidence supporting one type of fixation over another. In this study, we compared the biomechanical fixation of a reverse total shoulder glenoid baseplate secured with locking or non-locking peripheral screws. MethodsBoth a non-augmented mini baseplate with full backing support and an augmented baseplate were testing after implantation in solid rigid polyurethane foam. Each baseplate was implanted with a 30 mm central compression screw and four peripheral screws, either locking or non-locking (15 mm anterior/posterior and 30 mm superior/inferior). A 1 Hz cyclic force of 0-750 N was applied at a 60o angle for 5000 cycles. Throughout the test, the displacement of the baseplate was measured using a 3D Digital Image Correlation System. FindingsThe amount of migration measured in the both the non-augmented and augment cases shows no significant differences between locking and non-locking cases at the final cycle count (non-augment: 5.66 +/− 2.29 μm vs. 3.71 +/− 1.23 μm; p = 0.095, augment: 15.43 +/− 8.49 μm vs. 12.46 +/− 3.24 μm; p = 0.314). Additionally, the amount of micromotion measured for both sample types shows the same lack of significant difference (non-augment: 10.79 +/− 5.22 μm vs. 10.16 +/− 7.61 μm; p = 0.388, augment: 55.03 +/− 10.13 μm vs. 54.84 +/− 10.65 μm; p = 0.968). InterpretationThe presence of locking versus non-locking peripheral screws does not make a significant difference on the overall stability of a glenoid baseplate, in both a no defect case with a non-augmented baseplate and a bone defect case with an augmented baseplate.

Fracture mechanics based interpretation of the load sequence effect in the flexural fatigue behavior of concrete using digital image correlation

For a reliable and economical design of concrete structures subjected to fatigue loading, a comprehensive understanding and realistic prediction of concrete fatigue life under complex loading scenarios with variable amplitudes is of major concern. In this paper, experimental investigations of concrete behavior under monotonic, cyclic, and fatigue loading are presented with particular focus on the influence of loading sequence on fatigue life. Namely, a test campaign consisting of 32 three-point bending tests on notched beams was conducted, including two beam sizes and six different loading scenarios. Several response characteristics of the fatigue behavior including, fatigue creep curves, Wöhler curves, stiffness degradation, evolving shapes of hysteretic loops, and crack propagation aspects have been evaluated. In addition, the main dissipative mechanisms governing the flexural behavior of concrete under repeated loading were analyzed based on a wide range of loading scenarios. Furthermore, the effect of loading sequence has been studied and analyzed in detail with the help of a 3D digital image correlation (DIC) system. Based on these observations, a theoretical interpretation of the phenomenology behind the sequence effect under bending loading is provided considering the fatigue crack propagation aspects and the corresponding stress redistribution around the crack tip.

A Complex Review of the Possibilities of Residual Stress Analysis Using Moving 2D and 3D Digital Image Correlation System

Abstract Understanding the levels of residual stresses in the material is very important in predicting the service life of structural elements. One of the most widely used techniques to quantify them is the drilling method, where a small hole is milled in the structure. If the residual stresses are present, stress redistribution will occur, resulting in deformation of the hole surroundings. Nowadays, there is an effort to replace the conventionally used strain gauges, i.e. special strain gauge rosettes, with full-field optical experimental techniques. This paper deals with analysing the possibilities of measuring the relieved strains/stresses with a unique drilling/measuring device, which, unlike other non-commercial measuring systems, uses the moving digital image correlation (DIC) system. Since correlation systems do not tend to move during operation, an analysis was performed describing the effect of changing the position of the single and stereo camera correlation systems on the quality of the results of the strain/stress analysis performed in the vicinity of the milled hole. The conclusion from the analyses performed is that there is no significant accumulation of correlation errors during measurement. Therefore, the information on the magnitudes of the strains/stresses relieved obtained by the moving DIC system can be used to quantify the residual stresses with an expected error corresponding to the sensitivity of this full-field optical experimental technique.

P10. Sub-regional analysis of principal strains across the intact L3-4 disc during in vitro multi-directional loading using 3D digital image correlation (DIC)

P10. Sub-regional analysis of principal strains across the intact L3-4 disc during in vitro multi-directional loading using 3D digital image correlation (DIC)

3D digital image correlation system for monitoring of changes induced by RH fluctuations on parchment

One of the most common sources of damage in Cultural Heritage Objects (CHO) such as parchment, oil paintings and historical textiles is relative humidity (RH) changes which cause inplane and out-of-plane displacements of their surfaces. The best suited method which enables full-field, non-contact displacements measurement with high resolution and sufficient range, is 3D Digital Image Correlation (3D DIC). However, the standard version of DIC requires applying random, good contrast speckle pattern at a surface of the object under investigation. Such requirement is not acceptable for CHOs. In this paper, we analyze the possibility to apply 3D DIC method for monitoring of displacements in selected groups of CHOs without modifying their surface i.e. based on their natural texture. The selection of the data capturing conditions and analysis parameters can lead to successful non-invasive monitoring of CHOs’ behavior. The samples studied herein are historical parchments subjected to controlled RH changes that impose inplane and out-of-plane displacements variations in time.

Reverse Total Shoulder Arthroplasty Baseplate Stability in Superior Bone Loss With Augmented Implant

BackgroundGlenoid bone loss is commonly encountered in cases of rotator cuff tear arthropathy and can create challenges during reverse shoulder arthroplasty. In this study, we sought to investigate the biomechanical properties of a new treatment option for superior glenoid defect, an augmented reverse total shoulder baseplate.MethodsThree conditions were examined: non-augmented baseplate without defect, non-augmented baseplate with defect, and augmented baseplate with defect. The augmented baseplates included a 30-degree half wedge which also matched the created superior defect. The samples were cyclically loaded at a 60° simulated abduction angle to mimic baseplate loosening. The migration and micromotion of the baseplate were measured on the superior edge using a 3D Digital Image Correlation System.ResultsThe migration measured in the augmented baseplate showed no significant difference when compared to the no defect or defect cases. In terms of micromotion, the augmented baseplate showed values that were between the micromotions reported for the no defect and defect conditions, but not by a statistically significant amount.ConclusionThis study provides biomechanical evidence that augmented baseplates can reduce the amount of micromotion experienced by the RSA construct in the presence of significant superior glenoid bone deficiency, but do not fully restore stability to that of a full contact non-augmented baseplate.

Research paper: The three-dimensional mechanical response of orthodontic archwires and brackets in vitro during simulated orthodontic torque

Orthodontic archwire rotation around its long axis, known as third-order torque, is utilised to correct tooth rotational misalignments moving the tooth root closer to or away from the cheek through engagement with an orthodontic bracket. Studying the behaviour of archwire and brackets during an applied rotation can aid in better understanding and appreciating the mechanics of third-order torque, potentially allowing for more effective orthodontic treatment protocols. Mechanically characterising archwire behaviour during third-order torque application is a complex task due to their physical scale and geometries. An advanced measurement technique was needed to address these constraints. A three-dimensional (3D) non-contact optical method using a digital image correlation (DIC) system was developed. An orthodontic torque simulator (OTS) was used to apply and measure third-order torque with 0.483 × 0.635 mm (0.019″ x 0.025″) rectangular archwires in tandem with a 3D DIC system, whereby surface deformations and strains could be computed using correlation algorithms. The 3D DIC system was implemented to enable third-order torque experimentation with the OTS while imaging the archwire and bracket surfaces. The 3D DIC system's ability to measure 3D archwire deformations and strains was verified using a finite element model, where comparisons between 3D DIC measurements and calculated results from the model were made to ensure the measurement capabilities of 3D DIC in the context of third-order torque. The 3D DIC system was then used to compare archwire behaviour between stainless steel (SS) and titanium molybdenum alloy (TMA) archwires to study potential clinical differences in archwire behaviour, in which the archwires were rotated with a custom SS rigid dowel (RD) as well as commercial Damon Q orthodontic brackets. The quantification of third-order torque and archwire deformations and strains led to the conclusion that SS archwires led to larger torque magnitudes compared to TMA archwires. The RD resulted in larger archwire strains compared to Damon Q brackets. The 3D DIC system provides a non-contact measurement technique that can further be used with third-order torque experimentation with the OTS.

A simplified method for the evaluation of the layer compression test using one 3D digital image correlation system and considering the material anisotropy by the equibiaxial Lankford parameter

The layer compression test is an established method for the characterization of sheet metal behavior under equibiaxial tension. Due to its ability to achieve high strains without necking and the simple experimental setup, the test is a welcome alternative to the more complex Bulge test for flow curve determination. In addition, the layer compression test provides further data for the calibration of yield loci models. However, the evaluation of the test is not trivial, since a tactile extensometer measurement incorporates the error of closing gaps between single sheet layers. Moreover, the sheet metal anisotropy is neglected. To overcome the above-mentioned drawbacks, a measurement and evaluation methodology based on the optical strain measurement of two orthogonally positioned 3D digital image correlation (DIC) systems was introduced recently. The method delivers reliable results but increases the complexity and costs of the test. Here, a simplification to this method is proposed. By the usage of only one 3D DIC system, the major in-plane strain is acquired from an online measurement. The minor in-plane strain is calculated posteriori by the consideration of the biaxial Lankford parameter. In this way, the anisotropy and thus the correct flow behavior can be studied by only one 3D DIC system. The proposed method is evaluated and discussed.