Bondline Thickness Effects on Damage Tolerance of Adhesive Joints Subjected to Localized Impact Damages: Application to Leading Edge of Wind Turbine Blades

The leading edges of wind turbine blades are adhesively bonded composite sections that are susceptible to impact loads during offshore installation. The impact loads can cause localized damages at the leading edges that necessitate damage tolerance assessment. However, owing to the complex material combinations together with varying bondline thicknesses along the leading edges, damage tolerance investigation of blades at full scale is challenging and costly. In the current paper, we design a coupon scale test procedure for investigating bondline thickness effects on damage tolerance of joints after being subjected to localized impact damages. Joints with bondline thicknesses (0.6 mm, 1.6 mm, and 2.6 mm) are subjected to varying level of impact energies (5 J, 10 J, and 15 J), and the dominant failure modes are identified together with analysis of impact kinematics. The damaged joints are further tested under tensile lap shear and their failure loads are compared to the intact values. The results show that for a given impact energy, the largest damage area was obtained for the thickest joint. In addition, the joints with the thinnest bondline thicknesses displayed the highest failure loads post impact, and therefore the greatest damage tolerance. For some of the thin joints, mechanical interlocking effects at the bondline interface increased the failure load of the joints by 20%. All in all, the coupon scale tests indicate no significant reduction in failure loads due to impact, hence contributing to the question of acceptable localized damage, i.e., damage tolerance with respect to static strength of the whole blade.     

Experimental and Numerical Comparison of Impact Behavior between Thermoplastic and Thermoset Composite for Wind Turbine Blades

Damage generated due to low velocity impact in composite plates was evaluated focusing on the design and structural integrity of wind turbine blades. Impact properties of composite plates manufactured with thermoplastic and thermoset resins for different energy levels were measured and compared. Specimens were fabricated using VARTM (vacuum assisted resin transfer molding), using both matrix systems in conjunction with carbon, glass and carbon/glass hybrid fibers in the NCF (non-crimp fabric) architecture. Resin systems used were ELIUM 188O (thermoplastic) from Arkema Co., Ltd. and a standard epoxy reference, EPR-L20 from Hexion Co., Ltd. (thermoset). Auxiliary numerical finite element analyses were performed to better understand the tests physics. These models were then compared with the experimental results to verify their predictive capacity, given the intrinsic limitations due to their simplicity. Based in the presented results, it is possible to observe that ELIUM is capable to replace a conventional thermoset matrix. The thermoplastic panels presented similar results compared to its thermoset counterparts, with even a trend of less impact damage. Additionally, for both thermoplastic and thermoset resin systems, glass layups showed the lowest levels of damage while carbon panels presented the highest damage levels. Hybrid laminates can be applied as a compromise solution.     

The Natural History of Asymptomatic Gallstones: A Longitudinal Study and Prediction Model

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Development and Validation of a Risk Prediction Model for Atherosclerotic Cardiovascular Disease in Japanese Adults: The Hisayama Study

Aim: To develop and validate a new risk prediction model for predicting the 10-year risk of atherosclerotic cardiovascular disease (ASCVD) in Japanese adults. Methods: A total of 2,454 participants aged 40–84 years without a history of cardiovascular disease (CVD) were prospectively followed up for 24 years. An incident ASCVD event was defined as the first occurrence of coronary heart disease or atherothrombotic brain infarction. A Cox proportional hazards regression model was used to construct the prediction model. In addition, a simplified scoring system was translated from the developed prediction model. The model performance was evaluated using Harrell’s C statistics, a calibration plot with the Greenwood-Nam-D’Agostino test, and a bootstrap validation procedure. Results: During a median of a 24-year follow-up, 270 participants experienced the first ASCVD event. The predictors of the ASCVD events in the multivariable Cox model included age, sex, systolic blood pressure, diabetes, serum high-density lipoprotein cholesterol, serum low-density lipoprotein cholesterol, proteinuria, smoking habits, and regular exercise. The developed models exhibited good discrimination with negligible evidence of overfitting (Harrell’s C statistics: 0.786 for the multivariable model and 0.789 for the simplified score) and good calibrations (the Greenwood-Nam-D’Agostino test: P =0.29 for the multivariable model, 0.52 for the simplified score). Conclusion: We constructed a risk prediction model for the development of ASCVD in Japanese adults. This prediction model exhibits great potential as a tool for predicting the risk of ASCVD in clinical practice by enabling the identification of specific risk factors for ASCVD in individual patients.     

The Portacaval-Shunted Rat: A New Model for the Study of the Mechanisms Controlling Voluntary Ethanol Consumption and Ethanol Preference?

Portacaval anastomosis (PCA) is a surgical procedure whereby blood from the portal vein is shunted into the inferior vena cava. PCA in the rat results in a significant increase (from 0.77 ± 0.26 to 3.51 ± 0.37 g of ethanol/kg/day) in voluntary ethanol consumption in a free-choice paradigm between water and 5% ethanol solution. After PCA surgery, increased voluntary ethanol consumption starts abruptly at 6 to 7 days and is maintained for > 28 weeks. Voluntary ethanol consumption in rats after PCA results in blood ethanol levels up to 158 mg%. After PCA, the ethanol preference ratio (defined as the percentage of total fluid intake constituted by ethanol) increased from 19 ± 2% to 78 ± 2% ( p < 0.001). Administration of the nonselective opioid receptor antagonist naloxone (5 mg/kg, sc) resulted in a significant 6-fold attenuation of voluntary ethanol consumption by rats with PCA, an effect that was not mediated by an effect on locomotor activity. These findings, together with previous reports of widespread alterations of the μ- and δ-opioid receptors in the brain after PCA, suggest that increased voluntary ethanol consumption and ethanol preference in PCA rats may result from activation of the endogenous opioid system. Preliminary studies suggest that rats with PCA manifest behavioral signs consistent with the development of dependence. The portacaval-shunted rat may provide a useful preparation for the study of mechanisms, in particular those involving the liver, implicated in the development of increased voluntary ethanol consumption and ethanol preference.