69.3: A Mechanics Framework for Ion‐Exchanged Cover Glass with a Deep Compression Layer

Price, James J.; Glaesemann, G. Scott; Clark, Donald A.; Gross, Timothy M.; Barefoot, K.

doi:10.1889/1.3256467

Cited by 18 publications

(12 citation statements)

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“…Sharp contact is defined by the response of the glass, where a local contact exceeds the elastic limit and results in a permanent impression in the glass surface. Sharp contact is the primary failure mode in ion-exchanged cover glass (Price et al, 2009). Failure occurs during drops onto irregular, hard surfaces that generate large median/radial cracks originating in the subsurface of a sharp contact impression that penetrate the depth of compressive layer (DOL) and enter the central tension (CT) region.…”

Section: Introductionmentioning

confidence: 99%

“…Crack extension through the depth of layer typically occurs with minimal assistance from bend induced stresses since most devices utilize a design that keeps the cover glass fairly rigid. The Vickers indentation cracking test is used to measure the resistance to the formation of large median/ radial cracks under controlled/repeatable testing conditions in a rigid configuration and closely replicates the failure mechanism seen in cover glass in the field (Price et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

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Vickers Indentation Cracking of Ion-Exchanged Glasses: Quasi-Static vs. Dynamic Contact

Gross

Price

2017

Front. Mater.

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The indentation deformation and cracking responses of ion-exchanged glasses were measured using quasi-static and dynamic loading cycles. Two glass types were compared, a normal glass that deforms to a large extent by a shearing mechanism and a damage-resistant glass that comparatively deforms with less shear and more densification. The quasi-static indentation cracking threshold for median/radial cracks for the ion-exchanged normal glass was determined to be 7 kgf, while the ionexchanged damage-resistant glass required loads exceeding 30 kgf. The increased cracking threshold of the damage-resistant glass composition is attributed to the deformation mechanism, i.e., deformation with greater densification/less shear results in less subsurface damage and less residual stress. Both glass types were also subjected to dynamic indentation where the contact event time was more than 10,000 times shorter than the quasi-static condition. Under dynamic loading conditions, the cracking thresholds of the ion-exchanged normal and damage-resistant glasses increased to greater than 50 kgf and greater than 150 kgf, respectively. The stress-induced optical retardation was compared for quasi-static and dynamic indents made at sub-cracking threshold loads for both glasses. For indents made at the same sub-cracking threshold load in the normal glass, optical retardation mapping indicates less residual stress surrounding dynamic indents when compared to quasi-static indents. This suggests a rate dependence on the deformation mechanism in normal glasses with higher rates promoting densification in favor of shear. However, for damage-resistant glass, the stress-induced optical retardation is the same for indents made at both quasi-static and dynamic indentation rates.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Vickers Indentation Cracking of Ion-Exchanged Glasses: Quasi-Static vs. Dynamic Contact

Gross

Price

2017

Front. Mater.

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“…Intrinsic damage resistance by composition design and extrinsic surface strengthening methods, such as ion exchange (Cooper and Krohn, 1969;Mackenzie and Wakaki, 1980;Price et al, 2009;Varshneya, 2010) and thermal tempering (Gardon, 1980), are the key for improving the performance of oxide glasses against contact cracking. Such strengthening methods are ubiquitous in commercial applications, including cover glasses for electronic devices, high pressure windows, security and safety glasses, etc.…”

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confidence: 99%

Competing Indentation Deformation Mechanisms in Glass Using Different Strengthening Methods

et al. 2016

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Chemical strengthening via ion exchange, thermal tempering, and lamination are proven techniques for the strengthening of oxide glasses. For each of these techniques, the strengthening mechanism is conventionally ascribed to the linear superposition of the compressive stress (CS) profile on the glass surface. However, in this work, we use molecular dynamics simulations to reveal the underlying indentation deformation mechanism beyond the simple linear superposition of compressive and indentation stresses. In particular, the plastic zone can be dramatically different from the commonly assumed hemispherical shape, which leads to a completely different stress field and resulting crack system. We show that the indentation-induced fracture is controlled by two competing mechanisms: the CS itself and a potential reduction in free volume that can increase the driving force for crack formation. Chemical strengthening via ion exchange tends to escalate the competition between these two effects, while thermal tempering tends to reduce it. Lamination of glasses with differential thermal expansion falls in between. The crack system also depends on the indenter geometry and the loading stage, i.e., loading versus after unloading. It is observed that combining thermal tempering or high free volume content with ion exchange or lamination can impart a relatively high CS and reduce the driving force for crack formation. Therefore, such a combined approach might offer the best overall crack resistance for oxide glasses.

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“…In addition, if glass is scratched the cover lens becomes more susceptible to cracking [5]. The integrity of a hard coated plastic lens is not affected by scratches.…”

Section: Resultsmentioning

confidence: 99%

“…In addition, if the surface of glass is scratched it reduces the strength of the glass, making it more susceptible to cracking. [5].Hard coated plastic lens have been used on some feature phones and other limited applications. The drawbacks have been poor durability and a "plastic feel" and appearance.…”

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confidence: 99%

26.2: Super Durable Cover Lens Film

Pokorný

Toy

Cross

et al. 2014

Symp Digest of Tech Papers

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A new, hard coated cover lens film for the display industry is described. Interference fringing is drastically reduced through the use of a novel primer. The mechanism of failure in abrasion and scratch testing is explained along with the implications of this for designing a robust cover lens film. Author KeywordsHard coat; abrasion resistance; interference fringing; pencil hardness; cover lens; ObjectiveThe goal of this program is to provide the display industry an alternative to glass for cover lens applications. While glass manufacturers have made great improvements in cover glass properties [1], glass still suffers from high weight, converting challenges, ease of fracture and splinter, high cost, and poor flexibility. In addition, if the surface of glass is scratched it reduces the strength of the glass, making it more susceptible to cracking. [5].Hard coated plastic lens have been used on some feature phones and other limited applications. The drawbacks have been poor durability and a "plastic feel" and appearance. Another challenge for the industry is that several scratch and abrasion tests are used which makes performance comparison of various coatings to glass difficult. Unfortunately, the results from these different tests tend not to correlate with each other. 3M has produced nanoparticle reinforced hard coats for over 20 years. During this time, the properties of the hard coats have been greatly improved and additional functionality has been added. Current functional hard coats include features such as: anti-glare, easy cleanability, fingerprint fading, antireflection, anti-linting, and abrasion resistance. We have now developed a new hard coat with extremely high abrasion resistance while retaining flexibility and hardness.

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69.3: A Mechanics Framework for Ion‐Exchanged Cover Glass with a Deep Compression Layer

Cited by 18 publications

References 4 publications

Vickers Indentation Cracking of Ion-Exchanged Glasses: Quasi-Static vs. Dynamic Contact

Vickers Indentation Cracking of Ion-Exchanged Glasses: Quasi-Static vs. Dynamic Contact

Competing Indentation Deformation Mechanisms in Glass Using Different Strengthening Methods

26.2: Super Durable Cover Lens Film

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