scholarly journals In Situ Digital Image Correlation Observations of Laser Forming

Metals ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 17 ◽  
Author(s):  
Herman Fidder ◽  
Joris P. J. Admiraal ◽  
Václav Ocelík ◽  
Jeff Th. M. De Hosson
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Heat Affected Zone ◽  
Laser Power ◽  
Pure Titanium ◽  
Processing Parameters ◽  
Image Correlation ◽  
Laser Forming ◽  
Bending Angle

In this study experimental and modelling methods are used to examine the microstructural and bending responses of laser-formed commercially pure titanium grade 2. The in situ bending angle response is measured for different processing parameters utilizing 3D digital image correlation. The microstructural changes are observed using electron backscatter diffraction. Finite element modelling is used to analyse the heat transfer and temperature field inside the material. It has been proven that the laser bending process is not only controlled by processing parameters such as laser power and laser beam scanning speed, but also by surface absorption. Grain size appears to have no influence on the final bending angle, however, sandblasted samples showed a considerably higher final bending angle. Experimental and simulation results suggest that the laser power has a larger influence on the final bending angle than that of the laser transverse speed. The microstructure of the laser heat-affected zone consists of small refined grains at the top layer followed by large elongated grains. Deformation mechanisms such as slip and twinning were observed in the heat-affected zone, where their distribution depends on particular processing parameters.

scholarly journals Digital Image Correlation for Evaluation of Cracks in Reinforced Concrete Bridge Slabs

2021 ◽  
Vol 6 (7) ◽  
pp. 99
Author(s):  
Christian Overgaard Christensen ◽  
Jacob Wittrup Schmidt ◽  
Philip Skov Halding ◽  
Medha Kapoor ◽  
Per Goltermann
Keyword(s):  
Reinforced Concrete ◽  
Digital Image Correlation ◽  
Crack Initiation ◽  
Laboratory Test ◽  
Digital Image ◽  
Crack Detection ◽  
Image Correlation ◽  
In Situ Tests ◽  
Stop Criterion

In proof-loading of concrete slab bridges, advanced monitoring methods are required for identification of stop criteria. In this study, Two-Dimensional Digital Image Correlation (2D DIC) is investigated as one of the governing measurement methods for crack detection and evaluation. The investigations are deemed to provide valuable information about DIC capabilities under different environmental conditions and to evaluate the capabilities in relation to stop criterion verifications. Three Overturned T-beam (OT) Reinforced Concrete (RC) slabs are used for the assessment. Of these, two are in situ strips (0.55 × 3.6 × 9.0 m) cut from a full-scale OT-slab bridge with a span of 9 m and one is a downscaled slab tested under laboratory conditions (0.37 × 1.7 × 8.4 m). The 2D DIC results includes full-field plots, investigation of the time of crack detection and monitoring of crack widths. Grey-level transformation was used for the in situ tests to ensure sufficient readability and results comparable to the laboratory test. Crack initiation for the laboratory test (with speckle pattern) and in situ tests (plain concrete surface) were detected at intervals of approximately 0.1 mm to 0.3 mm and 0.2 mm to 0.3 mm, respectively. Consequently, the paper evaluates a more qualitative approach to DIC test results, where crack indications and crack detection can be used as a stop criterion. It was furthermore identified that crack initiation was reached at high load levels, implying the importance of a target load.

Methodology for in situ stress intensity factor determination on cracked structures by digital image correlation

2010 ◽  
Vol 1 (4) ◽  
pp. 344-357 ◽  
Author(s):  
V. Richter‐Trummer ◽  
P.M.G.P. Moreira ◽  
S.D. Pastrama ◽  
M.A.P. Vaz ◽  
P.M.S.T. de Castro
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Digital Image Correlation ◽  
Intensity Factor ◽  
Digital Image ◽  
Strain Field ◽  
Image Correlation ◽  
Content Type ◽  
Cracked Structures

PurposeThe purpose of this paper is to develop a methodology for in situ stress intensity factor (SIF) determination that can be used for the analysis of cracked structures. The technique is based on digital image correlation (DIC) combined with an overdetermined algorithm.Design/methodology/approachThe linear overdeterministic algorithm for calculating the SIF based on stress values around the crack tip is applied to a strain field obtained by DIC.FindingsAs long as the image quality is sufficiently high, a good accuracy can be obtained for the measured SIF. The crack tip can be automatically detected based on the same strain field. The use of the strain field instead of the displacement field, eliminates problems related to the rigid body motion of the analysed structure.Practical implicationsIn future works, based on the applied techniques, the SIF of complex cracked plane stress structures can be accurately determined in real engineering applications.Originality/valueThe paper demonstrates application of known techniques, refined for other applications, also the use of stress field for SIF overdeterministic calculations.

scholarly journals Multi-Scale Digital Image Correlation Analysis of In Situ Deformation of Open-Cell UHMWPE Foam

2020 ◽  
Author(s):  
Eugene S. Statnik ◽  
Codrutza Dragu ◽  
Cyril Besnard ◽  
Alexander J.G. Lunt ◽  
Alexey I. Salimon ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
High Performance ◽  
Structural Evolution ◽  
Image Correlation ◽  
Deformation Bands ◽  
Open Cell ◽  
Polyether Ether Ketone ◽  
Structural Levels

Porous ultra-high molecular weight polyethylene (UHMWPE) is a high performance bioinert polymer used in cranio-facial reconstructive surgery in procedures where relatively low mechanical stresses arise. As an alternative to much stiffer and costly polyether-ether-ketone (PEEK) polymer, UHMWPE finds further wide application in hierarchically structured hybrids for advanced implants mimicking cartilage, cortical and trabecular bone tissues within a single component. The mechanical behaviour of open-cell UHMWPE sponges obtained through sacrificial desalination of hot compression-moulded UHMWPE-NaCl powder mixtures shows a complex dependence on the fabrication parameters and microstructural features. In particular, similarly to other porous media it displays significant inhomogeneity of strain that readily localises within deformation bands that govern the overall response. In this article, we report advances in the development of accurate experimental techniques for operando studies of the structure-performance relationship applied to the porous UHMWPE medium with pore sizes of about 250 µm that are most well-suited for live cell proliferation and fast vascularization of implants. Samples of UHMWPE sponges were subjected to in situ compression using a micromechanical testing device within Scanning Electron Microscope (SEM) chamber, allowing the acquisition of high-resolution image sequences for Digital Image Correlation (DIC) analysis. Special masking and image processing algorithms were developed and applied to reveal the evolution of pore size and aspect ratio. Key structural evolution and deformation localisation phenomena were identified at both macro- and micro-structural levels in the elastic and plastic regimes. The motion of pore walls was quantitatively described, and the presence and influence of strain localisation zones were revealed and analysed using DIC technique.

Bending Deformation of Pure Titanium Plate in CO2 Laser Forming

2007 ◽  
Vol 329 ◽  
pp. 625-630 ◽  
Author(s):  
Koichi Okuda ◽  
Y. Sugie ◽  
Masayuki Nunobiki
Keyword(s):  
Co2 Laser ◽  
Laser Power ◽  
Pure Titanium ◽  
Laser Spot ◽  
Laser Forming ◽  
Titanium Plate ◽  
Bending Angle ◽  
Spot Diameter ◽  
Bending Deformation ◽  
Laser Spot Diameter

This study deals with behaviour of bending deformation in CO2 laser forming process of titanium. CO2 laser forming technique was applied for a pure titanium plate with thickness of 1 mm to aim the development of new bending process. The experiments of laser forming were carried out with a CO2 laser machine. The bending angle and the temperature of workpiece were examined under the condition of various laser power, feed speed and laser spot diameter. Based on the experimental results, it was found that the bending deformation behaved greatly depending on the laser power and the laser spot diameter. The bending angle increased with an increase in the laser power. The bending direction tended to change from the laser irradiation side to its opposite side when the large laser spot diameter was applied.

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