This paper focuses on extensive ductile crack growth by modeling a mode I fracture experiment. Solution of this problem, requires structural scale plate/shell finite which cannot resolve the details of the fracture process. Thus, a cohesive zone model, which accounts for the dependence of the cohesive tearing energy on the crack advance is employed. The steady-state cohesive energy is informed by the detailed analysis of necking localization and shear failure, performed with the Gurson model. The structural scale model reveals the partition of the tearing energy into the cohesive energy and the additional plastic dissipation occurring outside the cohesive zone.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSelectivity in organic group transfer in reactions of mixed lithium diorganocupratesW. Harry Mandeville and George M. WhitesidesCite this: J. Org. Chem. 1974, 39, 3, 400–405Publication Date (Print):February 1, 1974Publication History Published online1 May 2002Published inissue 1 February 1974https://pubs.acs.org/doi/10.1021/jo00917a027https://doi.org/10.1021/jo00917a027research-articleACS PublicationsRequest reuse permissionsArticle Views359Altmetric-Citations83LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Ceramics exhibit macroscopic stress/strain rate relations that should lead to superplastic extension. However, premature fracture is normally encountered, due to the formation and growth of grain‐boundary cavities. Thus, cavity nucleation and growth were analyzed in an attempt to identify microstructures and/or strain‐rate regimes that would suppress cavity evolution and hence allow superplasticity. Analysis of cavity nucleation indicates that fine‐grained materials devoid of grain‐boundary amorphous phases and inclusions should sustain substantial deformation rates without nucleating cavities, especially if solid‐solution additions that encourage rapid grain‐boundary diffusion (while not excessively decreasing surface energy) are identified. The analysis of void growth indicates that high relative surface diffusivities are also desirable, indicating that alloy additions that do not depress (and probably enhance) the relative surface diffusivities must be selected.
Growing layers on elastic substrates are capable of creating a wide variety of surface morphologies. Moderate growth generates a regular pattern of sinusoidal wrinkles with a homogeneous energy distribution. While the critical conditions for periodic wrinkling have been extensively studied, the rich pattern formation beyond this first instability point remains poorly understood. Here, we show that upon continuing growth, the energy progressively localizes and new complex morphologies emerge. Previous studies have often overlooked these secondary bifurcations; they have focused on large stiffness ratios between layer and substrate, where primary instabilities occur early, long before secondary instabilities emerge. We demonstrate that secondary bifurcations are particularly critical in the low stiffness ratio regime, where the critical conditions for primary and secondary instabilities move closer together. Amongst all possible secondary bifurcations, the mode of period-doubling plays a central role – it is energetically favourable over all other modes. Yet, we can numerically suppress period-doubling, by choosing boundary conditions, which favour alternative higher order modes. Our results suggest that in the low stiffness regime, pattern formation is highly sensitive to small imperfections: surface morphologies emerge rapidly, change spontaneously and quickly become immensely complex. This is a common paradigm in developmental biology. Our results have significant applications in the morphogenesis of living systems where growth is progressive and stiffness ratios are low.
This paper describes the compatibility of poly(dimethylsiloxane) (PDMS) with organic solvents; this compatibility is important in considering the potential of PDMS-based microfluidic devices in a number of applications, including that of microreactors for organic reactions. We considered three aspects of compatibility: the swelling of PDMS in a solvent, the partitioning of solutes between a solvent and PDMS, and the dissolution of PDMS oligomers in a solvent. Of these three parameters that determine the compatibility of PDMS with a solvent, the swelling of PDMS had the greatest influence. Experimental measurements of swelling were correlated with the solubility parameter, δ (cal1/2 cm-3/2), which is based on the cohesive energy densities, c (cal/cm3), of the materials. Solvents that swelled PDMS the least included water, nitromethane, dimethyl sulfoxide, ethylene glycol, perfluorotributylamine, perfluorodecalin, acetonitrile, and propylene carbonate; solvents that swelled PDMS the most were diisopropylamine, triethylamine, pentane, and xylenes. Highly swelling solvents were useful for extracting contaminants from bulk PDMS and for changing the surface properties of PDMS. The feasibility of performing organic reactions in PDMS was demonstrated by performing a Diels−Alder reaction in a microchannel.
Background: Increasing evidence supports a biologically plausible association between delayed conception and metabolic dysfunction, including insulin resistance and inflammation; however, few studies have assessed whether infertility is associated with metabolic diseases such as type 2 diabetes (T2D) later in life. Objective: We prospectively evaluated the association between a history of infertility and T2D risk in a large cohort of women. Methods: Participants of the Nurses’ Health Study II self-reported their infertility status (>12 months attempting a pregnancy), lifestyle characteristics, and several health-related outcomes, via biennial questionnaires (1989-2011). Those reporting infertility were asked to cite the clinical reason(s), if known. Exposure status was updated every two years and carried forward to represent “ever”. Cox proportional hazards models estimated the relative risk (HR) and 95% confidence interval (CI) comparing participants with a history of infertility versus none. Multivariable models adjusted for age, body mass index (BMI), physical activity, healthful dietary pattern score, smoking, alcohol consumption, and several other lifestyle factors. Results: Participants (N=115,750) were on average 35 years old (range 25-44) with a BMI of 24.1 (SD=5.0) at baseline, with 91.7% Caucasian. Twenty-one percent (n=24,118) reported a history of infertility at baseline or follow-up. Incident T2D was reported in 5,414 participants during follow-up (2.6 cases/1,000 person-years). Women with a history of infertility had a significant 21% greater risk of T2D compared to women without infertility after adjusting for several T2D risk factors (multivariable HR=1.21, CI=1.14, 1.29). Infertility due to ovulation disorders was associated with a 47% greater risk of T2D (HR=1.47, CI=1.33, 1.64), and tubal blockage with a 32% greater risk (HR=1.32, CI=1.09, 1.61), compared to no infertility. Other reasons for infertility were not associated with T2D risk, including cervical mucus disorder (HR=1.09, CI=0.80, 1.48), male factor (HR=1.13, CI=0.96, 1.32), and “other” (HR=1.08, CI=0.90, 1.28). Tests for interaction did not indicate significant effect modification across BMI categories for total infertility (BMI<25: HR=1.34, CI=1.03, 1.74; BMI 25-29: HR=1.38, CI=1.18, 1.60; BMI 30+: HR=1.15, CI=1.07, 1.34; p-interaction=0.13). Effect modification by BMI category was suggested for infertility due to ovulation disorders (BMI<25: HR=2.14, CI=1.58, 3.67; BMI 25-29: HR=1.43, CI=1.08, 1.89; BMI 30+: HR=1.35, CI=1.20, 1.52; p-interaction=0.06). Conclusions: Among women, a history of infertility is significantly associated with T2D later in life, specifically infertility due to ovulation disorders and tubal blockage.