Indentation-induced subsurface tunneling cracks as a means for evaluating fracture toughness of brittle coatings

Chai, Herzl

doi:10.1007/s10704-009-9362-3

Cited by 8 publications

(14 citation statements)

References 27 publications

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“…The hoop is responsible for generating the radial cracks observed in figure 4(b). Our system consisted of a thin plate on a soft substrate, so that failure from flexural stresses always prevailed over failure from contact stress [21,22]. We confirmed this observation by interrupting a few puncture tests prior to the flexural fracture of the plate.…”

Section: Puncture Testssupporting

confidence: 57%

“…The glass plate shows several long radial cracks emanating from the tip of the needle, many of them reaching the edge of the plate (figure 4(b)). This type of crack behavior is a characteristic of a flexural failure of the glass plate [21,22]. Under the point force imposed by the needle the glass plate bends, and flexural stresses increase.…”

Section: Puncture Testsmentioning

confidence: 99%

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Fabrication, testing and modeling of a new flexible armor inspired from natural fish scales and osteoderms

et al. 2014

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Crocodiles, armadillo, turtles, fish and many other animal species have evolved flexible armored skins in the form of hard scales or osteoderms, which can be described as hard plates of finite size embedded in softer tissues. The individual hard segments provide protection from predators, while the relative motion of these segments provides the flexibility required for efficient locomotion. In this work, we duplicated these broad concepts in a bio-inspired segmented armor. Hexagonal segments of well-defined size and shape were carved within a thin glass plate using laser engraving. The engraved plate was then placed on a soft substrate which simulated soft tissues, and then punctured with a sharp needle mounted on a miniature loading stage. The resistance of our segmented armor was significantly higher when smaller hexagons were used, and our bio-inspired segmented glass displayed an increase in puncture resistance of up to 70% compared to a continuous plate of glass of the same thickness. Detailed structural analyses aided by finite elements revealed that this extraordinary improvement is due to the reduced span of individual segments, which decreases flexural stresses and delays fracture. This effect can however only be achieved if the plates are at least 1000 stiffer than the underlying substrate, which is the case for natural armor systems. Our bio-inspired system also displayed many of the attributes of natural armors: flexible, robust with 'multi-hit' capabilities. This new segmented glass therefore suggests interesting bio-inspired strategies and mechanisms which could be systematically exploited in high-performance flexible armors. This study also provides new insights and a better understanding of the mechanics of natural armors such as scales and osteoderms.

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Section: Puncture Testssupporting

confidence: 57%

Section: Puncture Testsmentioning

confidence: 99%

Fabrication, testing and modeling of a new flexible armor inspired from natural fish scales and osteoderms

et al. 2014

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“…Referring to Figure 1A for notation, the subsurface radial stress under the load, σ 0 , is given by Chai (2009). where d is the layer thickness, subscripts c and s indicate layer and substrate, and P is the applied load.…”

Section: Failure Analysismentioning

confidence: 99%

A Bilayer Method for Measuring Toughness and Strength of Dental Ceramics

Chai,

Russ,

Vardhaman

et al. 2024

J Dent Res

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The ever-increasing usage of ceramic materials in restorative dentistry necessitates a simple and effective method to evaluate flexural strength σF and fracture toughness KC. We propose a novel method to determine these quantities using a bilayer specimen composed of a brittle plate adhesively bonded onto a transparent polycarbonate substrate. When this bilayer structure is placed under spherical indentation, tunneling radial cracks initiate and propagate in the lower surface of the brittle layer. The failure analysis is based on previous theoretical relationships, which correlate σF with the indentation force P and layer thickness d, and KC with P and mean length of radial cracks. This work examines the accuracy and limitations of this approach using a wide range of contemporary dental ceramic materials. The effect of layer thickness, indenter radius, load level, and length and number of radial cracks are carefully examined. The accuracy of the predicted σF and KC is similar to those obtained with other concurrent test methods, such as biaxial flexure and 3-point bending (σF), and bending specimens with crack-initiation flaws ( KC). The benefits of the present approach include treatment for small and thin plates, elimination of the need to introduce a precrack, and avoidance of dealing with local material nonlinearity effects for the KC measurements. Finally, the bilayer configuration resembles occlusal loading of a ceramic restoration (brittle layer) bonded to a posterior tooth (compliant substrate).

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“…Numerous techniques have been proposed to evaluate the fracture toughness of thin films, such as tension [2][3][4][5][6][7], bending [8][9][10], buckling [11] and indentation [12][13][14][15][16] tests, which can be categorized into stressbased and energy-based methods [17]. For the stress-based methods, the toughness is obtained by measuring stress intensity factor following the ASTM standards.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of fracture toughness of ZrN hard coatings by internal energy induced cracking method

Huang

Chen

Wang

et al. 2014

Surface and Coatings Technology

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Indentation-induced subsurface tunneling cracks as a means for evaluating fracture toughness of brittle coatings

Cited by 8 publications

References 27 publications

Fabrication, testing and modeling of a new flexible armor inspired from natural fish scales and osteoderms

Fabrication, testing and modeling of a new flexible armor inspired from natural fish scales and osteoderms

A Bilayer Method for Measuring Toughness and Strength of Dental Ceramics

Evaluation of fracture toughness of ZrN hard coatings by internal energy induced cracking method

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