Stereomicroscopic optical method for the assessment of load transfer patterns across the wood-adhesive bond interphase

Holzforschung ◽  
2015 ◽  
Vol 69 (5) ◽  
pp. 653-660 ◽  
Author(s):  
Matthew Schwarzkopf ◽  
Lech Muszyński
Keyword(s):  
Mechanical Properties ◽  
Load Transfer ◽  
Mechanical Performance ◽  
Adhesive Bond ◽  
Wood Adhesive ◽  
Surface Strain ◽  
Image Correlation ◽  
Optical Measurements ◽  
Experimental Methodology ◽  
Full Field

Abstract The mechanical performance of wood-based composites is determined by the mechanical properties of their individual components and the effective load transfer between these components. In laminated wood composites, this load transfer is facilitated by the adhesive bond. The experimental methodology developed in this study measures and analyzes the full-field deformation and strain distributions across the loaded wood-adhesive interphase at a micromechanical level. Optical measurements were performed based on the principles of digital image correlation by a stereomicroscopic camera system. This system allows the monitoring of in-plane deformations as well as out-of-plane displacements, providing full-field 3D surface strain maps across the adhesive bond. These measurements can be used to improve the understanding of the load transfer between the adherents and the contribution of the adhesive to the mechanical properties of the bulk composite and serve as a quantitative input for numerical modeling and simulations aimed at the improvement of the products.

scholarly journals Bio-Inspired 3D Infill Patterns for Additive Manufacturing and Structural Applications

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 499 ◽  
Author(s):  
Jan Podroužek ◽  
Marco Marcon ◽  
Krešimir Ninčević ◽  
Roman Wan-Wendner
Keyword(s):  
Additive Manufacturing ◽  
Mechanical Performance ◽  
Peak Load ◽  
Fem Analysis ◽  
Material Model ◽  
Surface Strain ◽  
Image Correlation ◽  
Nonlinear Material ◽  
Full Field ◽  
Structural Applications

The aim of this paper is to introduce and characterize, both experimentally and numerically, three classes of non-traditional 3D infill patterns at three scales as an alternative to classical 2D infill patterns in the context of additive manufacturing and structural applications. The investigated 3D infill patterns are biologically inspired and include Gyroid, Schwarz D and Schwarz P. Their selection was based on their beneficial mechanical properties, such as double curvature. They are not only known from nature but also emerge from numerical topology optimization. A classical 2D hexagonal pattern has been used as a reference. The mechanical performance of 14 cylindrical specimens in compression is quantitatively related to stiffness, peak load and weight. Digital image correlation provides accurate full-field deformation measurements and insights into periodic features of the surface strain field. The associated variability, which is inherent to the production and testing process, has been evaluated for 3 identical Gyroid specimens. The nonlinear material model for the preliminary FEM analysis is based on tensile test specimens with 3 different slicing strategies. The 3D infill patterns are generally useful when the extrusion orientation cannot be aligned with the build orientation and the principal stress field, i.e., in case of generative design, such as the presented branching structure, or any complex shape and boundary condition.

Effect of Autoclave Cure Time and Surface Preparation on Film Adhesive Bond in Lightweight Material Joints

2018 ◽  
Author(s):  
Isotta Morfini ◽  
Luca Goglio ◽  
Giovanni Belingardi ◽  
Sayed A. Nassar
Keyword(s):  
Failure Mode ◽  
Load Transfer ◽  
Mechanical Performance ◽  
Surface Preparation ◽  
Adhesive Bond ◽  
Lap Joints ◽  
Mode Analysis ◽  
Bonding Parameters ◽  
Film Adhesive ◽  
Cure Time

This study investigates the effect of cure time and surface roughness on mechanical performance of single lap joints (SLJ). Test joints are made of aluminum/aluminum or aluminum/magnesium adherends that are autoclave-bonded using a commercially available film adhesive. Joint mechanical performance is assessed in terms of the static load transfer capacity (LTC), fatigue life and failure mode. Except for the cure time, all the rates of the other autoclave-bonding parameters are kept constant; namely, the level of cure temperature and pressure, as well as the rates of autoclave heating, cooling, pressurization and depressurization. Test data, failure mode analysis, discussion, observations and conclusions are provided.

Local Elasto-Plastic Identification of the Behaviour of Friction Stir Welds with the Virtual Fields Method

2011 ◽  
Vol 70 ◽  
pp. 135-140 ◽  
Author(s):  
G. Le Louëdec ◽  
M.A. Sutton ◽  
Fabrice Pierron
Keyword(s):  
Mechanical Properties ◽  
Digital Image Correlation ◽  
Digital Image ◽  
High Speed ◽  
Weld Zone ◽  
Spatial Variations ◽  
Image Correlation ◽  
Virtual Fields Method ◽  
Full Field ◽  
Friction Stir

Welding is one of the most popular joining technologies in industry. Depending on the materials to be joined, the geometry of the parts and the number of parts to be joined, there is a wide variety of methods that can be used. These joining techniques share a common feature: the material in the weld zone experiences different thermo-mechanical history, resulting in significant variations in material microstructure and spatial heterogeneity in mechanical properties. To optimize the joining process, or to refine the design of welded structures, it is necessary to identify the local mechanical properties within the different regions of the weld. The development of full-field kinematic measurements (digital image correlation, speckle interferometry, etc.) helps to shed a new light on this problem. The large amount of experimental information attained with these methods makes it possible to visualize the spatial distribution of strain on the specimen surface. Full-field kinematic measurements provide more information regarding the spatial variations in material behaviour. As a consequence, it is now possible to quantify the spatial variations in mechanical properties within the weld region through a properly constructed inverse analysis procedure. High speed tensile tests have been performed on FSW aluminium welds. The test was performed on an MTS machine at a cross-head speed of up to 76 mm/s. Displacement fields were measured across the specimen by coupling digital image correlation with a high-speed camera (Phantom V7.1) taking 1000 frames per second. Then, through the use of the virtual fields method it is possible to retrieve the mechanical parameters of the different areas of the weld from the strain field and the loading. The elastic parameters (Young’s modulus and Poisson’s ratio) are supposed to be constant through the weld. Their identification was carried out using the virtual fields method in elasticity using the data of the early stage of the experiment. Assuming that the mechanical properties (elastic and plastic) of the weld are constant through the thickness, the plastic parameters were identified on small sections through the specimen, using a simple linear hardening model. This method leads to a discrete identification of the evolution of the mechanical properties through the weld. It allows the understanding of the slight variations of yield stress and hardening due to the complexity of the welding process.

Non-Contact Technique for Characterizing Full-Field Surface Deformation of Shape Memory Polymers

2010 ◽  
Author(s):  
A. J. W. McClung ◽  
G. P. Tandon ◽  
K. E. Goecke ◽  
J. W. Baur
Keyword(s):  
Elastic Modulus ◽  
Shape Memory ◽  
Strain Measurement ◽  
Shape Memory Polymers ◽  
Material Behavior ◽  
Image Correlation ◽  
Optical Measurements ◽  
Transverse Strain ◽  
Strain Gages ◽  
Full Field

Thermally-actuated shape memory polymers (SMPs) typically display two phases separated by the glass transition temperature (Tg). At temperatures well below the Tg, the polymer exhibits a relatively high elastic modulus. Well above the Tg the elastic modulus drops by several orders of magnitude. In this high temperature region, SMP materials can achieve strain levels well above 100 %. The complex behavior of SMPs (stiffnesses dropping to the order of 1 GPa and extremely high strain levels) precludes the use of traditional strain gages and low-contact force extensometers. The present study presents a detailed expansion of state-of-the-art thermomechanical testing techniques used to characterize the material behavior of SMPs. An MTS environmental chamber with an observation window allows for non-contact optical measurements during testing. A laser extensometer is used for measurement and active control of axial strain. The upper limit on the strain rate capability of the laser extensometer is established. In addition, the photographic strain measurement method known as digital image correlation (DIC) is incorporated, allowing for full field measurement of axial and transverse strains of SMPs over a range of temperatures and strain rates. The strain measurements of the DIC and laser extensometer are compared to each other as well as to clip-on extensometers and strain gages. The comparisons provide insight into the limitations of the traditional strain measurement systems. A series of tensile tests are performed on a commercial SMP from 25 °C up to temperatures of 130 °C and strain levels above 100 %. The laser extensometer provides a robust method for controlling the strain in the gage section of the samples. In addition, results show that the full field measurements of both the axial and the transverse strain are essential for characterizing the constitutive response of SMPs at room and elevated temperatures.

Error Assessment of Blade Deformation Measurements on a Multi-Megawatt Wind Turbine Based on Digital Image Correlation

2015 ◽  
Author(s):  
Jan Winstroth ◽  
Joerg R. Seume
Keyword(s):  
Digital Image Correlation ◽  
Wind Turbine ◽  
Error Estimation ◽  
Digital Image ◽  
Rotor Blades ◽  
Image Correlation ◽  
Optical Measurements ◽  
Full Field ◽  
Out Of Plane ◽  
Plane Bending

Optical full-field measurement methods such as Digital Image Correlation (DIC) provide a new opportunity for measuring deformation and vibration in wind turbine rotor blades during operation, in high spatial and temporal resolution. Recent field tests on a multi-megawatt wind turbine have demonstrated the vast potential for full scale testing, however little is known about the overall accuracy of DIC measurements on wind turbines. The present work proposes using a virtual 3D wind turbine model for estimating the error associated with the optical measurements. The entire setup is simulated a priori and accurate error estimation becomes possible. The error estimation for a 3.2 MW wind turbine suggests that relative out-of-plane bending of the rotor blades can be measured with an accuracy of ±9.1 mm, relative in-plane bending of the rotor blades can be measured with an accuracy of ±10.2 mm, and relative blade torsion can be measured with an accuracy of ±0.07 deg. This corresponds to a relative error of 0.46% for out-of-plane bending, 1.11% for in-plane bending and 5.46% for blade torsion.

Measurement of Transient Dynamic Response of Circuit Boards of a Handheld Device During Drop Using 3D Digital Image Correlation

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
S. B. Park ◽  
Chirag Shah ◽  
Jae B. Kwak ◽  
Changsoo Jang ◽  
Soonwan Chung ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
High Speed ◽  
Image Correlation ◽  
Impact Response ◽  
Experimental Methodology ◽  
Full Field ◽  
Handheld Device ◽  
3D Digital Image Correlation ◽  
The Impact

In this work, a new experimental methodology for analyzing the drop impact response is assessed using a pair of high-speed digital cameras and 3D digital image correlation software. Two different test boards are subjected to Joint Electron Device Engineering Council (JEDEC) standard free-fall impact conditions of half-sine pulse of 1500 G in magnitude and 0.5 ms in duration. The drop is monitored using a pair of synchronized high-speed cameras at a rate of up to 15,000 frames per second. The acquired images are subsequently analyzed to give full-field dynamic deformation, shape, and strain over the entire board during and after impact. To validate this new methodology for analyzing the impact response, the in-plane strain as well as the out-of-plane acceleration at selected locations were measured simultaneously during the drop using strain gauge and accelerometers and were compared with those obtained using high-speed cameras and 3D digital image correlation presented in this paper. Comparison reveals excellent correlation of the transient behavior of the board during impact and confirms the feasibility of using the full-field measurement technique used in this study.

Fatigue Crack Growth Rates and Tensile Strength of Titanium Produced by Means of Selective Laser Melting

2014 ◽  
Vol 627 ◽  
pp. 305-308 ◽  
Author(s):  
Tomasz Brynk ◽  
Barbara Romelczyk ◽  
Zbigniew Pakiela ◽  
Tomasz Kurzynowski ◽  
Edward Chlebus
Keyword(s):  
Mechanical Properties ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Selective Laser Melting ◽  
Pure Titanium ◽  
Tensile Tests ◽  
Image Correlation ◽  
Laser Melting ◽  
Full Field

Mini-samples technique was utilized to determine mechanical properties of technically pure titanium produced by means of selective laser melting (SLM). Full-field digital image correlation (DIC) measurements and inverse method were applied for crack tip position and stress intensity factors calculations in the case of fatigue crack growth rate tests. DIC was also used for strain measurement during tensile tests on sub sized samples. There was studied the influence of samples orientation on the mechanical properties of mini-samples. Samples were cut out from rectangular cubes and were oriented with 0°, 45° or 90° angle to the direction of laser beam travel. There were also tested samples directly produced via SLM. Additionally microstructure observations were performed to verify the quality of SLM processed materials and explain mechanical properties variations.

scholarly journals A Probabilistic Approach with Built-in Uncertainty Quantification for the Calibration of a Superelastic Constitutive Model from Full-field Strain Data

2019 ◽  
Author(s):  
Harshad M Paranjape ◽  
Kenneth I. Aycock ◽  
Craig Bonsignore ◽  
Jason D. Weaver ◽  
Brent A. Craven ◽  
...  
Keyword(s):  
Machine Learning ◽  
Bayesian Inference ◽  
Constitutive Model ◽  
Probabilistic Approach ◽  
Surface Strain ◽  
Image Correlation ◽  
Full Field ◽  
Material Parameters ◽  
Superelastic Deformation ◽  
Calibration Approach

We implement an approach using Bayesian inference and machine learning to calibrate the material parameters of a constitutive model for the superelastic deformation of NiTi shape memory alloy. We use a diamond-shaped specimen geometry that is suited to calibrate both tensile and compressive material parameters from a single test. We adopt the Bayesian inference calibration scheme to take full-field surface strain measurements obtained using digital image correlation together with global load data as an input for calibration. The calibration is performed by comparing these two experimental quantities of interest with the corresponding results from a simulation library built with the superelastic forward finite element model. We present a machine learning based approach to enrich the simulation library using a surrogate model. This improves the calibration accuracy to the extent permitted by the accuracy of the underlying material model and also improves the computational efficiency. We demonstrate, verify, and partially validate the calibration results through various examples. We also demonstrate how the uncertainty in the calibrated superelastic material parameters can propagate to a subsequent simulation of fatigue loading. This approach is versatile and can be used to calibrate other models of superelastic deformation from data obtained using various modalities. This probabilistic calibration approach can become an integral part of a framework to assess and communicate the credibility of simulations performed in the design of superelastic NiTi articles such as medical devices. The knowledge obtained from this calibration approach is most effective when the limitations of the underlying model and the suitability of the training data used to calibrate the model are understood and communicated.

scholarly journals Digital image correlation-based point-wise inverse characterization of heterogeneous material properties of gallbladder in vitro

2014 ◽  
Vol 470 (2167) ◽  
pp. 20140152 ◽  
Author(s):  
Katia Genovese ◽  
Luciana Casaletto ◽  
Jay D. Humphrey ◽  
Jia Lu
Keyword(s):  
Mechanical Properties ◽  
Extracellular Matrix ◽  
Material Properties ◽  
Soft Tissues ◽  
Applied Pressure ◽  
Heterogeneous Material ◽  
Image Correlation ◽  
Surface Geometry ◽  
Stress Strain ◽  
Full Field

Continuing advances in mechanobiology reveal more and more that many cell types, especially those responsible for establishing, maintaining, remodelling or repairing extracellular matrix, are extremely sensitive to their local mechanical environment. Indeed, it appears that they fashion the extracellular matrix so as to promote a ‘mechanical homeostasis’. A natural corollary, therefore, is that cells will try to offset complexities in geometry and applied loads with heterogeneous material properties in order to render their local environment mechanobiologically favourable. There is a pressing need, therefore, for hybrid experimental–computational methods in biomechanics that can quantify such heterogeneities. In this paper, we present an approach that combines experimental information on full-field surface geometry and deformations with a membrane-based point-wise inverse method to infer full-field mechanical properties for soft tissues that exhibit nonlinear behaviours under finite deformations. To illustrate the potential utility of this new approach, we present the first quantification of regional mechanical properties of an excised but intact gallbladder, a thin-walled, sac-like organ that plays a fundamental role in normal digestion. The gallbladder was inflated to a maximum local stretch of 120% in eight pressure increments; at each pressure pause, the entire three-dimensional surface was optically extracted, and from which the surface strains were computed. Wall stresses in each state were predicted from the deformed geometry and the applied pressure using an inverse elastostatic method. The elastic properties of the gallbladder tissue were then characterized locally using point-wise stress–strain data. The gallbladder was found to be highly heterogeneous, with drastically different stiffness between the hepatic and the serosal sides. The identified material model was validated through forward finite-element analysis; both the configurations and the local stress–strain patterns were well reproduced.

scholarly journals Testing System for the Mechanical Properties of Small-Scale Specimens Based on 3D Microscopic Digital Image Correlation

Sensors ◽  
2020 ◽  
Vol 20 (12) ◽  
pp. 3530
Author(s):  
Xu Liu ◽  
Rongsheng Lu
Keyword(s):  
Mechanical Properties ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Three Dimensional ◽  
Image Correlation ◽  
Field Strain ◽  
Small Scale ◽  
Testing System ◽  
Shape Functions ◽  
Full Field

The testing of the mechanical properties of materials on a small scale is difficult because of the small specimen size and the difficulty of measuring the full-field strain. To tackle this problem, a testing system for investigating the mechanical properties of small-scale specimens based on the three-dimensional (3D) microscopic digital image correlation (DIC) combined with a micro tensile machine is proposed. Firstly, the testing system is described in detail, including the design of the micro tensile machine and the 3D microscopic DIC method. Then, the effects of different shape functions on the matching accuracy obtained by the inverse compositional Gauss–Newton (IC-GN) algorithm are investigated and the numerical experiment results verify that the error due to under matched shape functions is far larger than that of overmatched shape functions. The reprojection error is shown to be smaller than before when employing the modified iteratively weighted radial alignment constraint method. Both displacement and uniaxial measurements were performed to demonstrate the 3D microscopic DIC method and the testing system built. The experimental results confirm that the testing system built can accurately measure the full-field strain and mechanical properties of small-scale specimens.

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