Prediction of Crack-Opening Stress Levels for Service Loading Spectra
Notice bibliographique
Résumé
The fatigue lives of automotive components subjected to variable amplitude service loading are assumed to be dominated by a process of small crack growth. It is generally accepted that crack closure is responsible for most of the variation in fatigue crack growth rates and fatigue lives. This investigation examined the effect of different types and magnitudes of service loadings on crack closure behavior. Three different Society of Automotive Engineers (SAE) standard service load histories with different mean stresses were applied to notched specimens of a 2024-T351 aluminum alloy. The three spectra are the SAE Grapple Skidder history, which has a positive mean stress, the SAE Log Skidder history which has a zero mean stress, and the inverse of the SAE Grapple Skidder history which has a negative mean stress. A curve of maximum stress in the history versus fatigue life was constructed for each spectrum. The crack-opening stress (COS) levels were measured at frequent intervals in order to capture the behavior of the opening stress for each spectrum, for each of a set of scaled histories with different maximum stress ranges. A crack growth analysis based on a fracture mechanics approach was used to model the fatigue behavior of the aluminum alloy specimens for the given load spectra and stress ranges. The crack growth analysis was based on an effective strain-based intensity factor, a crack growth rate curve obtained during closure-free loading cycles, and a local notch strain calculation based on Neuber's rule. The COS levels were modeled assuming that the COS follows an exponential build-up formula that is a function of the difference between the current crack opening stress and the steady state crack opening stress of the given cycle unless this cycle is below the intrinsic stress range, or the maximum stress is below zero. However, the build-up only occurs when the crack-opening steady state stress level for the given cycle is higher than the previously calculated crack opening stress. The modeled crack opening stress level was in good agreement with the measured crack opening stress. The average of the measured crack opening stresses and those calculated using the model were nearly the same for all the histories examined. When these average crack-opening stresses were used in the life prediction model they gave predictions as good as those obtained by modeling COS on a cycle by cycle basis. In the interest of simplifying the use of COS in design the average COS was correlated with the frequency of occurrence of the cycle reducing the COS to the average level. The use of a COS level corresponding to the one in 200 cycle gave a conservative estimate of average COS for all the histories.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».