A Crack Detection Technique for Use With Brittle Materials

1986 ◽  
Vol 108 (3) ◽  
pp. 232-235 ◽  
Author(s):  
W. S. Sampath ◽  
T. C. Ramaraj ◽  
M. C. Shaw
Keyword(s):  
Crack Initiation ◽  
Propagation Velocity ◽  
Crack Detection ◽  
Gold Film ◽  
Crack Opening ◽  
Electrical Conductance ◽  
Brittle Materials ◽  
Metal Foil ◽  
Engineering Structures ◽  
Crack Propagation Velocity

Crack gages are sensors designed to monitor crack initiation and growth in engineering structures by alteration of electrical conductance. Present gages involve a thick (5 μm) metal foil on an even thicker polymer substrate and are not suitable for use on brittle materials where the crack opening is small. The new technique employs a very thin (300 Å) gold film sputtered on a nonconducting brittle specimen. The method also enables crack propagation velocity to be estimated.

Smart Coating Sensor Applied in Crack Detection for Aircraft

2013 ◽  
Vol 330 ◽  
pp. 383-388 ◽  
Author(s):  
Ma Bao Liu ◽  
Bin Bin Li ◽  
Jiang Tao Li ◽  
Yuan Yuan Lian
Keyword(s):  
Crack Initiation ◽  
Crack Detection ◽  
Low Cost ◽  
Surface Preparation ◽  
Protective Layer ◽  
Fatigue Cracking ◽  
Electric Resistance ◽  
Engineering Structures ◽  
Smart Coating

Monitoring fatigue cracking of large engineering structures is a costly and time-intensive process. The authors present a low-cost smart coating sensor (SCS) consisted of driving layer, sensing layer and protective layer typically that can detect crack initiation and growth. The results show that the smart coating sensor can detect cracks above 300μm, corresponding to the increment of the sensing layer’s electric resistance at the level of 0.05Ω. Therefore, the development of SCS is of importance significance in the substitution of an existed inspection that requires substantial disassembly and surface preparation, and, thus, can find numerous applications in difficult-to-access locations on aircrafts.

Detection of Crack Travel and Opening of a Standard Notched Specimen Mode I Using Embedded FOS Device

2013 ◽  
Vol 442 ◽  
pp. 360-366 ◽  
Author(s):  
F.E. Utou ◽  
J. Gryzagoridis ◽  
B. Sun
Keyword(s):  
Optical Fiber ◽  
Light Beam ◽  
Fiber Optics ◽  
Optical Fibers ◽  
Crack Detection ◽  
Crack Opening ◽  
Engineering Structures ◽  
Notched Specimen ◽  
Sensing System ◽  
Total Failure

Crack detection and monitoring has become one of a focus center for the health monitoring of engineering structures under the influence of mechanical deformation.This paper discusses the detecting, tracking and monitoring mechanisms for the crack, by initiating a sensing system by using a standard notched specimen. Crack features such as magnitude of crack travel versus crack opening are displacement indicators that can vary due to the applied load on the normal line to the direction of the crack travel. More ever, the rate of the crack opening is considered to be proportional to the rate of the crack travel.Lines of three optical fibers of 125 nm are embedded and fixed at two ends and pass across the direction of the crack travel at an approximation of 2mm apart. The light of 2V from the source is passed through the optical fiber, across the crack tip. The crack opening forces the optical fiber to extend under tension, and hence the interruption of its diameter. This causes the decrease in the light intensity traveling through the fiber till the total failure of the fiber, to declare presence of crack. The embedded fiber optics on the specimen links the instrumentation optical system which permits the light beam throughput. Finally the converted light beam into voltage domain allowed us to closely analyze the crack tendency, and eventually be able to establish a model and sensor equation which governs the trend of the crack growth.

scholarly journals Harmfulness Defect in Double-Notched Specimen of S533 Steel

2020 ◽  
Vol 9 (4) ◽  
pp. 2287-2293
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Finite Element Methods ◽  
Propagation Velocity ◽  
Test Specimen ◽  
Crack Opening ◽  
Concentration Coefficient ◽  
Notched Specimen ◽  
Crack Propagation Velocity ◽  
Stress Concentration Coefficient

The analytical solving of fracture mechanics equations remains insufficient for complex mechanisms, hence the use of finite element methods (FEM). The paper considered a test specimen with double S355 steel notches, stressed in tension, causing crack opening with two planes of symmetry. The refinement of the mesh is carried out at the bottom of the notch using the elements of Barsoum. The stress concentration coefficient and the crack propagation velocity are evaluated.

Development of a scanning laser crack detection technique for corrosion fatigue testing of fine wire

1995 ◽  
Vol 10 (2) ◽  
pp. 372-380 ◽  
Author(s):  
Paul A. Schmidt ◽  
James C. Earthman
Keyword(s):  
Crack Initiation ◽  
Corrosion Fatigue ◽  
Crack Detection ◽  
Fatigue Testing ◽  
Crack Opening ◽  
Laser System ◽  
Detection Technique ◽  
Scanning Laser ◽  
Growth Monitoring ◽  
Metallic Wires

A scanning laser crack detection technique has been developed for use in corrosion fatigue testing of fine metallic wires. The technique has been integrated into a computerized data acquisition and control system allowing the unattended operation of extended fatigue tests. The system is capable of detecting cracks with surface lengths as small as 100 μm, with crack opening displacements as low as 1 μm. Detection schemes of light loss and light scattering have been successfully used to monitor crack initiation in air and in 0.9% sodium chloride solution. The present scanning laser system has been used for crack initiation detection in over 50 fatigue experiments and has the potential for use in crack growth monitoring. The method can provide information concerning other surface phenomena in addition to the study of cracks. The technique has potential applications beyond metallic wires, including fibers used in optics and ceramic reinforcement fibers used in structural composites.

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 Extremely Thin Metal Foil Blades as Cutting Tools for Hard and Brittle Materials

2018 ◽  
Vol 221 ◽  
pp. 04006
Author(s):  
Satoshi Sakamoto ◽  
Sanshiro Akaoka ◽  
Masaya Gemma ◽  
Yasuo Kondo ◽  
Kenji Yamaguchi ◽  
...  
Keyword(s):  
Particle Size ◽  
Abrasive Particle ◽  
Brittle Materials ◽  
Groove Depth ◽  
Thin Metal ◽  
Metal Foil ◽  
Machining Time ◽  
Blade Thickness ◽  
Hard And Brittle Materials ◽  
Thin Metal Foil

The manufacturing costs of semiconductor products such as silicon wafers can be reduced by decreasing the kerf loss. In addition, a decrease in the kerf loss leads to an effective utilization of rare materials, which is environmentally beneficial from the viewpoint of saving resources. This study aims to reduce the kerf loss during slicing hard and brittle materials. Therefore, the possibility of using an extremely thin metal foil blade instead of a wire tool in slicing was examined. Initially, grooving characteristics using a metal foil blade (thickness: 50 μm or less) was investigated. The main conclusions are that grooving with a metal foil blade is possible and kerf loss can be reduced. The groove depth tends to increase as the machining time and particle size of abrasives increase. The groove width is smaller when a thin metal foil blade is used and vice versa. However, if the abrasive particle size is too large, grooving becomes impossible. Since the wear of metal foil blade increases with an increase in the particle size of the abrasive, it is necessary to use an abrasive with a particle size that is suitable for the thickness of the metal foil blade.

scholarly journals Experimental and Theoretical Determination of the Frost-Heave Cracking Law and the Crack Propagation Criterion of Slab Track with Water in the Crack

2019 ◽  
Vol 9 (21) ◽  
pp. 4592 ◽  
Author(s):  
Fengzhuang Tong ◽  
Liang Gao ◽  
Xiaopei Cai ◽  
Yanglong Zhong ◽  
Wenqiang Zhao ◽  
...  
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Opening ◽  
Evaluation Criteria ◽  
Image Correlation ◽  
Frost Heave ◽  
External Temperature ◽  
Slab Track ◽  
Initiation And Propagation ◽  
Evolution Laws

Crack propagation produced by frost heave affects the durability of slab-track structures in high-humidity and cold regions in China. This work is intended to reveal the evolution laws of frost-heave crack propagation, establish evaluation criteria for crack propagation, and investigate factors involved in frost-heave crack propagation. Firstly, by preparing slab-track specimens with initial cracks, an experiment of frost-heave crack propagation was designed. The process of frost-heave crack propagation was carried out by means of digital image correlation (DIC) technology and acoustic emission (AE) technology, respectively. These experiments revealed the evolution laws of generalized strain and AE events’ location during crack initiation and propagation, respectively, and the key parameters of micro-crack initiation strain and unstable propagation strain were obtained. By using theoretical and experimental analysis, a double-strain criterion for frost-heave crack propagation was proposed. Finally, factors involved in frost-heave crack propagation were investigated. The results show that crack initiation can be reflected by the crack-tip strain. The average micro-crack initiation strain and unstable propagation strain were found to be 224 με and 243 με, respectively. Moreover, it was found that the frost-heave crack propagation was caused by an ice plug which formed at the crack opening. When the crack width is larger than 2.7 mm and the external temperature is lower than −6.6 °C, cracks propagate easily under the frost-heave force.

The Calculation of Stress Intensity Factors and the Analysis of Propagation Characteristic of Crack at Hole

2011 ◽  
Vol 250-253 ◽  
pp. 1856-1861
Author(s):  
Li Jun Lu ◽  
Jian Ping Liu ◽  
Zhong Mei Li
Keyword(s):  
Stress Intensity ◽  
Crack Propagation ◽  
Stress Intensity Factors ◽  
Propagation Velocity ◽  
Propagation Characteristic ◽  
Propagation Model ◽  
Intensity Factors ◽  
Crack Propagation Velocity ◽  
Guyed Mast ◽  
Shape And Size

This paper focusing on the crack at hole of guyed-mast’s ear-plate connecting cables and shaft of guyed-mast, adopting two degree of freedom crack propagation model, track the crack propagation according to the increment of the deepest point and the surface point on the crack front of crack at hole of guyed-mast’s ear-plate. The stress intensity factors of I,II and III type crack with given shape and size have been calculated via finite element method, and a numerical method of calculating stress intensity factors with any shape and size crack has been proposed; furthermore according to modified I, II and III type compound crack propagation velocity formula on the basis of Paris crack propagation velocity formula, we analyzed the changing of crack shape parameter a/c with crack size parameter a/T of crack at hole of ear-plate connecting cable and shaft of guyed-mast by numerical integration method and obtained the propagation characteristic.

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