scholarly journals An experimental study on the manufacture and characterization of in-plane fibre-waviness defects in composites

2018 ◽  
Vol 5 (5) ◽  
pp. 180082 ◽  
Author(s):  
W. J. R. Christian ◽  
F. A. DiazDelaO ◽  
K. Atherton ◽  
E. A. Patterson
Keyword(s):  
Residual Strain ◽  
Composite Structures ◽  
Computational Models ◽  
Image Correlation ◽  
Strain Fields ◽  
Strain Measurements ◽  
Ultrasound Measurements ◽  
Residual Strains ◽  
Failure Predictions

A new method has been developed for creating localized in-plane fibre waviness in composite coupons and used to create a large batch of specimens. This method could be used by manufacturers to experimentally explore the effect of fibre waviness on composite structures both directly and indirectly to develop and validate computational models. The specimens were assessed using ultrasound, digital image correlation and a novel inspection technique capable of measuring residual strain fields. To explore how the defect affects the performance of composite structures, the specimens were then loaded to failure. Predictions of remnant strength were made using a simple ultrasound damage metric and a new residual strain-based damage metric. The predictions made using residual strain measurements were found to be substantially more effective at characterizing ultimate strength than ultrasound measurements. This suggests that residual strains have a significant effect on the failure of laminates containing fibre waviness and that these strains could be incorporated into computational models to improve their ability to simulate the defect.

Direct Optical Estimation of Deformation Gradient Tensors Using Lucas-Kanade Digital Image Warping

2013 ◽  
Author(s):  
John J. Boyle ◽  
Guy M. Genin ◽  
Maiko Kume ◽  
Robert B. Pless ◽  
Stavros Thomopoulos
Keyword(s):  
Digital Image ◽  
Accurate Determination ◽  
Deformation Gradient ◽  
Biological Tissues ◽  
Magnetic Resonance Images ◽  
Image Correlation ◽  
Strain Fields ◽  
Established Technique

Mechanical characterization of inhomogeneous and/or geometrically complex biological tissues requires precise and accurate determination of strain fields. Digital image correlation is a well established technique for determining strain fields on the surfaces of deforming materials. The technique involves matching patterns between pairs of images to estimate the displacement of certain regions or features on a sample. 2 Image correlation has also been used to track deformations in dynamic magnetic resonance images of heart and brain. 3

Neutron Diffraction Residual Strain Measurements in Plasma Sprayed Nanostructured Hydroxyapatite Coatings for Orthopaedic Implants

2010 ◽  
Vol 652 ◽  
pp. 309-314 ◽  
Author(s):  
Rehan Ahmed ◽  
Nadimul Haque Faisal ◽  
Stefan M. Knupfer ◽  
Anna Maria Paradowska ◽  
Michael E. Fitzpatrick ◽  
...  
Keyword(s):  
Heat Treatment ◽  
Neutron Diffraction ◽  
Residual Strain ◽  
Strain Measurements ◽  
Strain Profile ◽  
Hydroxyapatite Coatings ◽  
Heat Treated ◽  
Residual Strains ◽  
Biomedical Coatings ◽  
Plasma Sprayed

Residual strains in plasma sprayed and heat-treated hydroxyapatite (HA) coatings deposited on a titanium alloy (Ti-6Al-4V) substrate were investigated by means of neutron diffraction. Strain measurements were performed in vertical scan (“z-scanning”) mode to provide a through thickness strain profile in the coating and substrate materials. Results are discussed in terms of the influence of heat-treatment on the residual strain profile of these biomedical coatings. This investigation concluded that the heat-treatment had a significant effect on the residual strain profile in HA coatings.

scholarly journals A novel specimen shape for measurement of linear strain fields by means of digital image correlation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Nedaa Amraish ◽  
Andreas Reisinger ◽  
Dieter Pahr
Keyword(s):  
Digital Image Correlation ◽  
Image Correlation ◽  
Strain Gauges ◽  
Linear Strain ◽  
Strain Fields ◽  
Strain Gradients ◽  
Full Field ◽  
Strain Measurements ◽  
Deformation Stages ◽  
Specimen Shape

AbstractStrains on the surface of engineering structures or biological tissues are non-homogeneous. These strain fields can be captured by means of Digital Image Correlation (DIC). However, DIC strain field measurements are prone to noise and filtering of these fields influences measured strain gradients. This study aims to design a novel tensile test specimen showing two linear gradients, to measure full-field linear strain measurements on the surface of test specimens, and to investigate the accuracy of DIC strain measurements globally (full-field) and locally (strain gauges’ positions), with and without filtering of the DIC strain fields. Three materials were employed for this study: aluminium, polymer, and bovine bone. Normalized strain gradients were introduced that are load independent and evaluated at two local positions showing 3.6 and 6.9% strain change per mm. Such levels are typically found in human bones. At these two positions, two strain gauges were applied to check the experimental strain magnitudes. A third strain gauge was applied to measure the strain in a neutral position showing no gradient. The accuracy of the DIC field measurement was evaluated at two deformation stages (at $$\approx $$ ≈ 500 and 1750 μstrain) using the root mean square error (RMSE). The RMSE over the two linear strain fields was less than 500 μstrain for both deformation stages and all materials. Gaussian low-pass filter (LPF) reduced the DIC noise between 25% and 64% on average. As well, filtering improved the accuracy of the local normalized strain gradients measurements with relative difference less than 20% and 12% for the high- and low-gradient, respectively. In summary, a novel specimen shape and methodological approach are presented which are useful for evaluating and improving the accuracy of the DIC measurement where non-homogeneous strain fields are expected such as on bone tissue due to their hierarchical structure.

Residual Strains in ITER Conductors by Neutron Diffraction

2014 ◽  
Vol 777 ◽  
pp. 84-91 ◽  
Author(s):  
Stefanus Harjo ◽  
Tsutomu Hemmi ◽  
Jun Abe ◽  
Wu Gong ◽  
Yoshihiko Nunoya ◽  
...  
Keyword(s):  
Residual Strain ◽  
High Field ◽  
Performance Test ◽  
Strain Difference ◽  
Thermal Strain ◽  
Field Zone ◽  
Cross Sectional ◽  
Strain Measurements ◽  
Peak Broadening ◽  
Residual Strains

Measurements of internal strains in the superconducting constituent (Nb3Sn phase in Nb3Sn strand) in two cable-in-conduit conductors (CICC) for International Thermonuclear Experimental Reactor were performed using an engineering materials diffractometer TAKUMI of J-PARC. From strain measurements in a CICC for the toroidal field magnet after a performance test of cyclic current, in 100 mm long cut bars, a peak broadening and a large relaxation on residual strain were observed in Nb3Sn phase at a portion received a high magnetic field (high field zone). Internal strain measurements were also conducted in a CICC for the central solenoidal magnets after the similar performance test, in the full-size shape as used in the performance test (3.6 m long) and in 100 mm long cut bars. Three main results were obtained. (1) Residual strain difference before and after the cutting to 100 mm long bar was about 0.1%, (2) a large relaxation on residual thermal strain was observed at the high field zone, and (3) the large relaxation on residual thermal strain at the high field zone was found mainly in a cross sectional side where the Lorentz force coming in.

Computational Models for Multilayered Composite Shells with Application to Tires

1996 ◽  
Vol 24 (1) ◽  
pp. 11-38 ◽  
Author(s):  
G. M. Kulikov
Keyword(s):  
Type Theory ◽  
Computational Models ◽  
Geometrical Nonlinearity ◽  
Higher Order ◽  
Stress Strain ◽  
Strain Fields ◽  
First Order ◽  
Timoshenko Type ◽  
Joint Influence ◽  
Discrete Layer

Abstract This paper focuses on four tire computational models based on two-dimensional shear deformation theories, namely, the first-order Timoshenko-type theory, the higher-order Timoshenko-type theory, the first-order discrete-layer theory, and the higher-order discrete-layer theory. The joint influence of anisotropy, geometrical nonlinearity, and laminated material response on the tire stress-strain fields is examined. The comparative analysis of stresses and strains of the cord-rubber tire on the basis of these four shell computational models is given. Results show that neglecting the effect of anisotropy leads to an incorrect description of the stress-strain fields even in bias-ply tires.

scholarly journals Shear Capacity of Reinforced Concrete Beams under Monotonic and Cyclic Loads: Experiments and Computational Models

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4092
Author(s):  
Kamil Bacharz ◽  
Barbara Goszczyńska
Keyword(s):  
Reinforced Concrete ◽  
Laboratory Tests ◽  
Computational Models ◽  
Concrete Beams ◽  
Shear Capacity ◽  
Reinforced Concrete Beams ◽  
Image Correlation ◽  
Engineering Practice ◽  
Cyclic Loads ◽  
Loading Modes

The paper reports the results of a comparative analysis of the experimental shear capacity obtained from the tests of reinforced concrete beams with various static schemes, loading modes and programs, and the shear capacity calculated using selected models. Single-span and two-span reinforced concrete beams under monotonic and cyclic loads were considered in the analysis. The computational models were selected based on their application to engineering practice, i.e., the approaches implemented in the European and US provisions. Due to the changing strength characteristics of concrete, the analysis was also focused on concrete contribution in the shear capacity of reinforced concrete beams in the cracked phase and on the angle of inclination of diagonal struts. During the laboratory tests, a modern ARAMIS digital image correlation (DIC) system was used for tracking the formation and development of diagonal cracks.

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