Fatigue Crack Propagation Threshold

Marci, G.; Castro, D. E.; Bachmann, V.

doi:10.1520/jte11530j

Cited by 29 publications

(2 citation statements)

References 16 publications

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“…The maximum SERR or G value of a load cycle was calculated using the following equation [20]:

G_{\max} goodbreak= \frac{italicnδ P_{\max}}{2 italicBa}

where n , δ , P max , B , and n are the slope of the linear compliance to crack length relationship, load point displacement, maximum applied force within the load cycle, specimen width, and crack length, respectively. Displacement‐controlled fatigue experiments allow to deduce the fatigue threshold at high cycle numbers and very low crack propagation rates below 10 −6 mm/cycle [21, 22]. The fatigue threshold SERR is a measure of the minimum amount of energy required to propagate a crack or more generally cause an increase in compliance.…”

Section: Methodsmentioning

confidence: 99%

Environmental fatigue crack growth of PV glass/EVA laminates in the melting range

Riedl,

Haselsteiner,

Säckl

et al. 2024

Progress in Photovoltaics

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The delamination of encapsulants in photovoltaic (PV) modules is a common issue that leads to power loss due to optical losses. Encapsulant debonding is usually examined under monotonic loading conditions subsequent to environmental exposure such as damp heat. Service‐relevant, superimposed environmental‐mechanical fatigue loads are not considered adequately. Hence, the environmental fatigue delamination resistance of thermally toughened double glass laminates with an ethylene vinyl acetate copolymer (EVA) adhesive layer was investigated in this study. Focus was given to the melting range of EVA, in which the non‐crosslinked crystalline phase fraction is already in the partly molten state. Double cantilever beam specimens were tested on an electrodynamic test machine at temperatures of 60, 70, 80, and 90°C and relative humidity (rh) levels of 2%, 30%, 50%, and 80%. The fractured surfaces were characterized by digital microscopy, Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and differential scanning calorimetry (DSC). The cyclic fatigue tests revealed a decay in delamination resistance at elevated temperature and humidity levels. At 70°C, the delamination resistance was low, regardless of the relative humidity. Most of the laminates failed by debonding. XPS analysis showed a reduction of the C=O and C–O content, along with an increase in Si–O content with increasing relative humidity. For laminates tested at 60 and 70°C, an EVA recrystallization peak was observed in DSC experiments. This peak was shifted to significantly higher temperatures at 80% rh. XPS and DSC indicated local hydrolysis within the porous fracture process zone ahead of the crack tip. Consequently, acetic acid formation led to a decrease in delamination resistance, resulting in lower fatigue threshold values. The investigations confirmed the significant impact of environmental conditions on the fatigue delamination resistance within glass/encapsulant laminates. Notably, acetic acid formation and a significant reduction in delamination properties were observed after around 100 h of environmental fatigue exposure.

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“…The maximum SERR or G value of a load cycle was calculated using the following equation [20]:

G_{\max} goodbreak= \frac{italicnδ P_{\max}}{2 italicBa}

Section: Methodsmentioning

confidence: 99%

Environmental fatigue crack growth of PV glass/EVA laminates in the melting range

Riedl,

Haselsteiner,

Säckl

et al. 2024

Progress in Photovoltaics

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“…Fatigue crack propagation is a complex phenomenon that is not yet fully understood, although many studies 38) have been dedicated to understanding the mechanism behind metal fatigue since it was first observed in 1829. 9,10) The fatigue propagation threshold in Ti6Al4V was first measured by Marci et al 11) Afterwards, several variables affecting the fatigue threshold were determined, including the stress ratio R (= K max /K min , where K max and K min are the maximum and minimum of the applied stress intensity factor, respectively), crack closure, and short fatigue cracks. It has been established that the contribution of R to the change in the threshold stress intensity range is a crucial parameter determining crack growth characteristics.…”

Section: Introductionmentioning

confidence: 99%

Effects of Temperature and Stress Ratio on Stage II Fatigue Crack Propagation in Bimodal Ti–6Al–4V

et al. 2021

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The temperature dependence of the fatigue crack propagation rate in stage IIb in bimodal Ti6Al4V was investigated at different stress ratios R. Fatigue tests were conducted between room temperature and 550 K at R of 0.1, 0.7, 0.8, and 0.9, and two phenomena were elucidated consequently. First, the fatigue crack growth rates were nearly temperature independent for R = 0.1, 0.7, and 0.8 while it is temperature dependent at R = 0.9. This difference in the temperature dependence can be explained by the assumptions that the fatigue crack growth is controlled by the dislocation activities associated with work-hardening for R¯0.8 while it is controlled by dislocation glide at R = 0.9. Second, the fatigue crack growth rates at R = 0.9 was higher than those at R = 0.1, 0.7, and 0.8. This increase in the fatigue crack growth rate at R = 0.9 can be explained by the change in the stress intensity factor of crack opening. Both the controlling mechanisms emanated from the change in the dislocation structure in front of the crack tip.

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Ermüdungsschwellwert: Materialeigenschaft und Auslegungsparameter

Marci

Castro

Bachmann

et al. 1990

Materialwissenschaft Werkst

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Der Ermiidungsschwellwert wird durch zwei experimentelle Versuchsmethoden fur den gesamten Zugschwellbereich bestimmt. Dabei stellen die beiden Versuchsmethoden die den Zugschwellbereich begrenzenden Ermudungsbelastungen dar. Eine dritte Versuchsmethode positioniert den Schwellwert zwischen K,,, und K,,,, wobei der Schwellwertaufgrund des ,,Closure"-Parameters KO, -nicht unter 0,5 K,,, positioniert zu werden braucht. Die gewonnenen Ergebnisse zeigen, daB der Ermudungsschwellwert unter allen Ermudungsbelastungen existiert undje nach Werkstoffeine Materialkonstante bzw. eine von K, , , abhangige KenngroBe ist. Fatigue Crack Propagation Threshold: Material Property and Design CriteriaThe fatigue crack propagation threshold has been determined by two experimental methods covering the tension-tension fatigue regime. The two experimental methods are boundary conditions for this fatigue regime. A third experimental method positions the threshold somewhere between K, , , and K,i, such that because of the ,,Closure Parameter KO," the threshold is not positioned below 0.5 K,,,. The results obtained show that a threshold exists under all fatigue loading conditions and -depending on the subject material is either a material property or a material parameter which depends on K,,,. ,/Kmax Verhaltnis von Unterspannung zur Oberspannung da/dN Riflfortschrittsgeschwindigkeit AKth unteres Ende einer da/dN -AK-Kurve AKo Ermudungsschwellwert ohne ,,Closure", ermittelt unter speziellen Ermudungsbelastungen AKT Ermudungsschwellwert ohne ,,Closure", ermittelt unter generellen Ermudungsbelastungen (fur die meisten Werkstoffe ist AKo = AKT) Ende des Bereiches, in dem Bruchflachenkontakt erfolgt Aufteilungs(Grenz-)punkt fur die Auftcilung des AK in den Bereich, in dem ErmudungsriRfortschritt erfolgen kann (AKeff), meist als ,,KO,'' bezeichnet AK = Kmax -Kmm KO, KG e Lastverhaltnis beim Jump-in-Versuch 6

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Fatigue Crack Propagation Threshold

Cited by 29 publications

References 16 publications

Environmental fatigue crack growth of PV glass/EVA laminates in the melting range

Environmental fatigue crack growth of PV glass/EVA laminates in the melting range

Effects of Temperature and Stress Ratio on Stage II Fatigue Crack Propagation in Bimodal Ti–6Al–4V

Ermüdungsschwellwert: Materialeigenschaft und Auslegungsparameter

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