Damage analysis of deployable thin-walled composite shell structure during coiling up
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Damage tolerance
This study is to investigate the compressive strength of the carbon/epoxy thick laminate after damage. Through damage tolerance of thick laminate is not standardized test because specimens exceed typical specimen thickness described in the ASTM standard, design allowable of thick laminate shall be determined by the experiment to address design criteria of the structure and incorporate functional capability with damage level. In this study, it is performed the research on damage tolerance of thick laminate adopting aircraft structure. The damage tolerance of thick laminates such as no damage and impact damage is evaluated under compression loading.
Damage tolerance
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Several methods are available for the measurement of strength of paper in the thickness direction. However, the values obtained from these methods are highly correlated with each other and also with the in-plane strength measurements. The relationship between z-direction tensile strength and in-plane tensile index of handsheets made at varying extents of pulp beating, types of strength aids and doses of strength aids has been studied. It has been noticed that the z-direction tensile strength of paper can be expressed in terms of in-plane tensile index by a single relationship whether the tensile index is changed by refining, or by adding strength aids, or by increasing the dose of the strength aid. In practice, an appropriate value of tensile index may be specified to ensure adequate performance of the paper even when it is subjected to stresses in z-direction.
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The effects of the tensile rate and samples preparation method on tensile strength and elongation after fracture for PP and PS were studied.The results showed that tensile strength of PP and PS increased with the increasing of tensile rate.But the elongation after fracture of these two materials presented different changes.The tensile strength and elongation after fracture of injection molding samples of PS were much higher than the compression molding samples of PS.The elongation after fracture of injection molding samples of PP increased 69% than the compression molding samples,but the tensile strength did not change obviously.
Elongation
Molding (decorative)
Compression molding
Tensile testing
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Vehicle stiffness is a commonly used parameter in the field of vehicle safety. But a single-valued “stiffness”, although well defined for the linear case, is not well defined for non-linear systems, such as vehicle crashes. Moreover, the relationship between vehicle stiffness and mass remains confusing. One previous work [Vehicle Mass and Stiffness: Search for a Relationship, G. Nusholtz, SAE2004, 04CONG--17, 2004 SAE International Congress, March, Detroit, USA, 2004] addresses this issue. Multiple definitions of stiffness were used to address the lack of a clear definition of stiffness. The R-squared values for the correlation between mass and each stiffness measure were presented. The results showed that no clear relationship existed between mass and any of the stiffness measures. The results from a statistical analysis indicated that there were differences in stiffness between different types of vehicles. This paper extends the same research by including a significant amount of new data samples as well as some different analysis procedures. Results show that mass is poorly correlated to stiffness and for some vehicle types mass correlates better to vehicle crush than to stiffness. In addition, it is shown that even without a well-defined definition of stiffness different levels of stiffness can be defined and differences in stiffness between different vehicle types can be quantitatively and qualitatively established.
Direct stiffness method
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This tensile test is to mimic the worst-case scenario of the swab being caught on an obstruction when being pulled out of the nasopharyngeal space. It is to determine how much tensile force the swab can withstand without breaking. A variety of different swabs (different materials and different geometries) were tested using the protocol outlined in Section 2 (Tensile Testing Procedure). Not all of the swabs were pre-treated using the Autoclave. For those swabs that were pre-treated using the Autoclave, the tensile tests were performed within 6 hours of completion of the Autoclave pre-treatment, unless otherwise noted. The FormLabs-USF and FormLabs-Northwell were printed at LLNL using FormLabs Surgical Grade V1 Resin on a Form 3B Printer. Results Summary: All FormLabs design and treatment variations (e.g. autoclaving and “aging”) had higher tensile strength compared commercial swabs. Autoclaving degraded the tensile strength. “Aging” after autoclaving improved the tensile strength. “Aging” without autoclaving degraded the tensile strength. No differences were observed in tensile strength with different autoclaving protocols. No significant differences were observed in tensile strength for different batches.
Autoclave
Tensile testing
Universal testing machine
Breaking strength
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Abstract : Damage tolerance analysis, based on fracture mechanics, is an important tool for ensuring the safety of flight of airframes. Traditionally, these analyses are deterministic in nature, but probabilistic methods have been applied to damage tolerance analysis in limited cases. The purpose of this dissertation is to formulate probabilistic damage tolerance analyses for metallic structural components, based on U.S. Air Force damage tolerance philosophy for slow crack growth and fail safe components. A survey of the literature was conducted on probabilistic durability and damage tolerance methods. The important elements of the methods are covered; including the initial fatigue quality, the variability in crack growth rate, and the probability of crack detection. Probabilistic Methods, Damage Tolerance, Metallic Structures.
Damage tolerance
Airframe
Tolerance Analysis
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The airframe material selection criterion has paid more attention to the damage-tolerant properties with the establishment of durability and damage-tolerance design principle.Considering the actual bearing stress,the damage-tolerance properties can be characterized by the da/dN-3ΔK/σb curves during crack stationary propagation stage.The damage tolerance properties of the airframe metals are compared by using this method.The compared results show that this characterization could characterize the damage-tolerance properties of materials more comprehensively.The curves of stress vs.total fatigue life and crack propagation are plotted to evaluate the synthetic mechanical properties,and to enhance the accuracy of materials selection.On the other hand,the relationship between material properties and design requirements are established through these curves,this could guide the new material research and development.
Damage tolerance
Airframe
Material selection
Characterization
Material Design
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Abstract In this article, the concept of damage tolerance as it relates to aerospace grade carbon fiber polymeric composites is introduced. The goal of a damage tolerance approach is to ensure safety of a structural part even in the presence of an acceptable flaw or damage. Typical damage of concern is impact‐induced delamination, particularly, barely visible impact damage (BVID) wherein internal unseen delamination can be present and grow with service loading. Damage assessment using non destructive evaluation (NDE) techniques is critical. Compression after impact (CAI) has become an industry standard to evaluate residual strength, which is a good measure of effect of impact damage on laminate compressive design property. The overall damage tolerance approach is empirical and relies heavily on test data. More sophisticated combined analytical/computational/experimental methods are under development.
Damage tolerance
Delamination
Residual strength
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Scanning electron microscopy generally requires specimen preparation which includes dehydration or drying and metal coating. This preparation is necessary for beam sensitive specimens or specimens that contain water and/or oil. This has been a necessary requirement for quality imaging with conventional scanning electron microscopes (SEMs). Recently with the development of variable-pressure SEMs (VP-SEMs), scanning electron microscopy of most specimens has become possible without the need of specimen preparation. Water-containing wet specimens can be examined at low temperatures at which water vaporization is suppressed and specimen artifacts due to water evaporation are minimized.
Vaporization
Metal coating
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In order to meet increasing requirement for the evaluation and design of damage tolerance of brittle materials, a simple expression was proposed to estimate the damage tolerance quantitatively using basic material parameters, based on the features of damage tolerance and fracture mechanics. The calculated results from this equation indicated that the damage tolerance of nanolayer grained ceramics was over 10 times higher than that of some brittle ceramics, while glass has the lowest damage tolerance. Therefore, the damage tolerance of various ceramics can be estimated directly using their basic properties data without the necessity of additional tests. SEM examination and finite element simulation showed that the high damage tolerance of the layer grained ceramics was attributed to delamination in grains, interlocking microstructures and crack deflection.
Damage tolerance
Brittleness
Interlocking
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