Microstructure-Scale In-Situ Image Correlation-Based Study of Grain Deformation and Crack Tip Displacements in Al–Cu Alloys

2014 ◽  
Vol 4 (2) ◽  
pp. MPC20140041
Author(s):  
Vipul K. Gupta ◽  
Scott A. Willard ◽  
Jacob D. Hochhalter ◽  
Stephen W. Smith
Keyword(s):  
Crack Tip ◽  
Image Correlation ◽  
Cu Alloys

scholarly journals In Situ Measurements for Plastic Zone Ahead of Crack Tip and Continuous Strain Variation under Cyclic Loading Using Digital Image Correlation Method

Metals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 273 ◽  
Author(s):  
Yan Zhao ◽  
Dianyin Hu ◽  
Meng Zhang ◽  
Wei Dai ◽  
Weifang Zhang
Keyword(s):  
Digital Image Correlation ◽  
Plastic Zone ◽  
Crack Propagation ◽  
Digital Image ◽  
Crack Tip ◽  
Experimental Results ◽  
Image Correlation ◽  
Specimen Preparation ◽  
Strain Variation

Fatigue crack is one of the most common damage forms for aeronautical aluminum alloy. With crack propagation, the strain fields of the whole object surface and plastic zone (PZ) ahead of the crack tip are changing continuously. For most metallic materials, the behavior of PZ around the crack tip and continuous strain variation play a vital role in crack propagation. In this work, the “continuous” strain information at and in front of the crack tip on the specimen surface was obtained quantitatively and the PZ size ahead of crack tip was in situ measured quantitatively with crack propagation by using the digital image correlation (DIC) method, which overcomes the difficulty for the in situ measurement of mechanical variables. Moreover, the method of specimen preparation was simplified by using a white matt paint with strong adhesion, but also resulted in a higher resolution being shown, even for such a large area. Furthermore, the experimental results of the PZ size from the proposed method had good agreement with the theoretical values, which overcomes the limitation that the conventional approaches only consider the quasi-static crack. Finally, the continuous strain variation behavior was analyzed from the experimental results in detail with the consideration of crack propagation.

Influence of Martensitic Phase on Microcrack Propagation in a Ferritic-Martensitic Steel

2014 ◽  
Vol 891-892 ◽  
pp. 301-306 ◽  
Author(s):  
Angelika Brueckner-Foit ◽  
Pascal Pitz ◽  
Frank Zeismann ◽  
Lisa Zellmer
Keyword(s):  
Dual Phase Steel ◽  
Martensitic Steel ◽  
Crack Opening ◽  
Crack Tip ◽  
Relative Displacement ◽  
Image Correlation ◽  
X Ray ◽  
Crack Wake ◽  
Microcrack Propagation

Hard phases such as martensite regions affect micro-crack extension by blocking the plastic zone ahead of the crack tip, but also by changing the crack opening which can be taken as loading quantity for cracks. This paper deals with the measurement of crack opening for microcracks in a ferrite/martensite dual phase steel. The methods used are in-situ testing in the SEM, X-ray tomography, and digital image correlation. It was found that martensite regions affect the relative displacement of the crack phases both at the crack tip and in the crack wake.

3D/4D Strain Mapping Using In Situ X-Ray Microtomography

2011 ◽  
Vol 70 ◽  
pp. 249-254 ◽  
Author(s):  
Hiroyuki Toda ◽  
Kentaro Uesugi ◽  
Yoshio Suzuki ◽  
Masakazu Kobayashi
Keyword(s):  
Strain Distribution ◽  
Crack Tip ◽  
Local Strain ◽  
Image Correlation ◽  
Correlation Technique ◽  
In Situ Observation ◽  
Strain Mapping ◽  
X Ray ◽  
Discrete Crack

X-ray microtomography (XMT) has been utilized for the in-situ observation of various structural materials under external disturbance such as loading. In-situ XMT provides a unique possibility to access the three-dimensional (3D) character of internal microstructure and its time evolution behaviours non-destructively, thereby enabling advanced techniques for measuring local strain distribution. Local strain mapping is readily enabled by processing such high-resolution tomographic images either by the particle tracking technique or the digital image correlation technique. Procedures for tracking microstructural features which have been developed by the authors, have been applied to analyse localised deformation and damage evolution in a material. Typically several tens of thousands of microstructural features, such as particles and pores, are tracked in a tomographic specimen (0.2 - 0.3 mm3in volume). When a sufficient number of microstructural features is dispersed in 3D space, the Delaunay tessellation algorithm is used to obtain local strain distribution. With these techniques, 3D strain fields can be measured with reasonable accuracy. Even local crack driving forces, such as local variations in the stress intensity factor, crack tip opening displacement and J integral along a crack front line, can be measured from discrete crack tip displacement fields.

scholarly journals Experimental and Numerical Study on Plastic Zone Variation ahead of Fatigue Crack Tip

2018 ◽  
Vol 165 ◽  
pp. 06004
Author(s):  
Zhang Wei ◽  
Zhou Daoqing ◽  
Cai Liang
Keyword(s):  
Plastic Deformation ◽  
Fatigue Crack ◽  
Plastic Zone ◽  
Crack Growth ◽  
Crack Tip ◽  
Image Correlation ◽  
In Situ Observation ◽  
Crack Growth Behaviour ◽  
Single Overload

The plastic deformation ahead of crack tip is of great significance to analysis of the fatigue crack growth behaviour. Using the in-situ microscopy experiment technique, the variation of strain field in the vicinity of crack tip is investigated within load cycles at the small time scale. The contours of plastic zones are measured through the in-situ observation and digital image correlation (DIC). Finite element method (FEM) is also used to simulate the plasticity ahead of the crack tip. Furthermore, the numerical studies are extended to the single overload case to analyse the effect of large plastic zone on the subsequent crack growth. The evolution of residual stress is extracted by FEM simulation to explore the influence of plastic deformation before, during and after the single overload applied on the following crack propagation. Based on the FEM analysis, a model is proposed to approximate the size of the overload effect zone. Finally, some experimental data and numerical simulations are employed to validate this model.

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.

scholarly journals Optimisation Method for Determination of Crack Tip Position Based on Gauss-Newton Iterative Technique

2021 ◽  
Vol 34 (1) ◽  
Author(s):  
Bing Yang ◽  
Zhanjiang Wei ◽  
Zhen Liao ◽  
Shuwei Zhou ◽  
Shoune Xiao ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Plastic Zone ◽  
Relative Error ◽  
Crack Tip ◽  
Image Correlation ◽  
Preconditioned Conjugate Gradient ◽  
Loading Process ◽  
Tip Position

AbstractIn the digital image correlation research of fatigue crack growth rate, the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor, thereby affecting the life prediction. This paper proposes a Gauss-Newton iteration method for solving the crack tip position. The conventional linear fitting method provides an iterative initial solution for this method, and the preconditioned conjugate gradient method is used to solve the ill-conditioned matrix. A noise-added artificial displacement field is used to verify the feasibility of the method, which shows that all parameters can be solved with satisfactory results. The actual stress intensity factor solution case shows that the stress intensity factor value obtained by the method in this paper is very close to the finite element result, and the relative error between the two is only − 0.621%; The Williams coefficient obtained by this method can also better define the contour of the plastic zone at the crack tip, and the maximum relative error with the test plastic zone area is − 11.29%. The relative error between the contour of the plastic zone defined by the conventional method and the area of the experimental plastic zone reached a maximum of 26.05%. The crack tip coordinates, stress intensity factors, and plastic zone contour changes in the loading and unloading phases are explored. The results show that the crack tip change during the loading process is faster than the change during the unloading process; the stress intensity factor during the unloading process under the same load condition is larger than that during the loading process; under the same load, the theoretical plastic zone during the unloading process is higher than that during the loading process.

Mechanical Properties of Nanocrystalline Materials Produced by In Situ Consolidation Ball Milling

2008 ◽  
Vol 579 ◽  
pp. 15-28 ◽  
Author(s):  
Carl C. Koch ◽  
Khaled M. Youssef ◽  
Ron O. Scattergood
Keyword(s):  
Mechanical Properties ◽  
Ball Milling ◽  
Nanocrystalline Materials ◽  
Preparation Method ◽  
High Strength ◽  
Al Alloys ◽  
Ductile Metals ◽  
Cu Alloys ◽  
Bulk Nanocrystalline

This paper reviews a method, “in situ consolidation ball milling” that provides artifactfree bulk nanocrystalline samples for several ductile metals such as Zn, Al and Al alloys, and Cu and Cu alloys. The preparation method is described in this paper and examples of the mechanical behavior of nanocrystalline materials made by this technique are given. It is found that in such artifact-free metals, combinations of both high strength and good ductility are possible.

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