Thermoset/Thermoplastic Interphases: The Role of Initiator Concentration in Polymer Interdiffusion.

In the co-bonding of thermoset and thermoplastic polymers, the interdiffusion of the polymers results in the formation of an interphase between them. Understanding the factors influencing the interdiffusion and the resulting interphase is crucial in order to optimize the mechanical performance of the bond. Herein, for the first time, the effect of the initiator concentration of the thermoset resin-initiator mixture on the interphase thickness of co-bonded thermoset-thermoplastic polymers is investigated. The dependence of the gelation time on the initiator concentration is determined by rheometer measurements. Differential scanning calorimetry measurements are carried out to determine the speed of cure. To co-bond the polymers, pieces of already-manufactured thermoplastic plates are embedded in a resin-initiator mixture. The interphase thickness of the co-bonded polymers is measured with an optical microscope. The results of this study show that the gelation time decreases as the initiator concentration increases. This decrease leads to a significant reduction in both interphase thickness and diffusivity. For instance, increasing the initiator/resin weight ratio from 1% to 3% reduces the gelation time by 74% and the interphase thickness by 63%.

The Springer Model for Lifetime Prediction of Wind Turbine Blade Leading Edge Protection Systems: A Review and Sensitivity Study.

The wind energy sector is growing rapidly. Wind turbines are increasing in size, leading to higher tip velocities. The leading edges of the blades interact with rain droplets, causing erosion damage over time. In order to mitigate the erosion, coating materials are required to protect the blades. To predict the fatigue lifetime of coated substrates, the Springer model is often used. The current work summarizes the research performed using this model in the wind energy sector and studies the sensitivity of the model to its input parameters. It is shown that the Springer model highly depends on the Poisson ratio, the strength values of the coating and the empirically fitted a2 constant. The assumptions made in the Springer model are not physically representative, and we reasoned that more modern methods are required to accurately predict coating lifetimes. The proposed framework is split into three parts-(1) a contact pressure model, (2) a coating stress model and (3) a fatigue strength model-which overall is sufficient to capture the underlying physics during rain erosion of wind turbine blades. Possible improvements to each of the individual aspects of the framework are proposed.

Mesoscale Process Modeling of a Thick Pultruded Composite with Variability in Fiber Volume Fraction.

Pultruded fiber-reinforced polymer composites are susceptible to microstructural nonuniformity such as variability in fiber volume fraction (Vf), which can have a profound effect on process-induced residual stress. Until now, this effect of non-uniform Vf distribution has been hardly addressed in the process models. In the present study, we characterized the Vf distribution and accompanying nonuniformity in a unidirectional fiber-reinforced pultruded profile using optical light microscopy. The identified nonuniformity in Vf was subsequently implemented in a mesoscale thermal-chemical-mechanical process model, developed explicitly for the pultrusion process. In our process model, the constitutive material behavior was defined locally with respect to the corresponding fiber volume fraction value in different-sized representative volume elements. The effect of nonuniformity on the temperature and cure degree evolution, and residual stress was analyzed in depth. The results show that the nonuniformity in fiber volume fraction across the cross-section increased the absolute magnitude of the predicted residual stress, leading to a more scattered residual stress distribution. The observed Vf gradient promotes tensile residual stress at the core and compressive residual stress at the outer regions. Consequently, it is concluded that it is essential to take the effects of nonuniformity in fiber distribution into account for residual stress estimations, and the proposed numerical framework was found to be an efficient tool to study this aspect.

Co-Bonded Hybrid Thermoplastic-Thermoset Composite Interphase: Process-Microstructure-Property Correlation.

Co-bonding is an effective joining method for fiber-reinforced composites in which a prefabricated part bonds with a thermoset resin during the curing process. Manufacturing of co-bonded thermoset-thermoplastic hybrid composites is a challenging task due to the complexities of the interdiffusion of reactive thermoset resin and thermoplastic polymer at the interface between two plies. Herein, the interphase properties of co-bonded acrylonitrile butadiene styrene thermoplastic to unsaturated polyester thermoset are investigated for different processing conditions. The effect of processing temperature on the cure kinetics and interdiffusion kinetics are studied experimentally. The interphase thickness and microstructure are linked to the chemo-rheological properties of the materials. The interdiffusion mechanisms are explored and models are developed to predict the interphase thickness and microstructure for various process conditions. The temperature-dependent diffusivities were estimated by incorporating an inverse diffusion model. The mechanical response of interphases was analyzed by the Vickers microhardness test and was correlated to the processing condition and microstructure. It was observed that processing temperature has significant effect on the interdiffusion process and, consequently, on the interphase thickness, its microstructure and mechanical performance.

3D Numerical Modeling of Laser Assisted Tape Winding Process of Composite Pressure Vessels and Pipes-Effect of Winding Angle, Mandrel Curvature and Tape Width.

Advanced thermoplastic composites manufacturing using laser assisted tape placement or winding (LATP/LATW) is a challenging task as monitoring and predicting nip point (bonding) temperature are difficult especially on curved surfaces. A comprehensive numerical analysis of the heat flux and temperature distribution near the nip point is carried out in this paper for helical winding of fiber reinforced thermoplastic tapes on a cylindrically shaped mandrel. An optical ray-tracing technique is coupled with a numerical heat transfer model in the process simulation tool. The developed optical-thermal model predictions were compared with experimental data available in literature to validate its effectiveness. The influences of winding/placement angle, mandrel curvature and tape width on the incident angles, the laser absorbed intensity, and the process temperature distribution are studied extensively using the validated model. Winding/placement angle has a considerable effect on the temperature distribution. Increase in winding angle results in a higher temperature for tape due to more reflections coming from the substrate. On the other hand, substrate temperature decreases as the winding angle increases due to a decrease in the laser incident angles based on the local surface curvature. An increase in mandrel curvature results in higher nip point temperatures for substrate and lower one for tape. Different mandrel sizes for 90 ∘ placement path do not have a strong effect on the substrate process temperature as for other winding angles because of less curvature change of the corresponding irradiated area. Tape width causes local temperature variations at the edges of the tape/substrate. In order to obtain the desired process temeprature during LATW or LATP processes, the laser intensity distribution on the tape and substrate surfaces should be regulated.

A Review on the Mechanical Modeling of Composite Manufacturing Processes.

The increased usage of fiber reinforced polymer composites in load bearing applications requires a detailed understanding of the process induced residual stresses and their effect on the shape distortions. This is utmost necessary in order to have more reliable composite manufacturing since the residual stresses alter the internal stress level of the composite part during the service life and the residual shape distortions may lead to not meeting the desired geometrical tolerances. The occurrence of residual stresses during the manufacturing process inherently contains diverse interactions between the involved physical phenomena mainly related to material flow, heat transfer and polymerization or crystallization. Development of numerical process models is required for virtual design and optimization of the composite manufacturing process which avoids the expensive trial-and-error based approaches. The process models as well as applications focusing on the prediction of residual stresses and shape distortions taking place in composite manufacturing are discussed in this study. The applications on both thermoset and thermoplastic based composites are reviewed in detail.

Can Hounsfield unit values of the cortex and papillae determined by computed tomography demonstrate the possibility of kidney stone formation?

PURPOSE: This study is aimed at measuring HU values of the renal cortex and papillae in patients with nephrolithiasis and demonstrating renal changes associated with nephrolithiasis. MATERIALS AND METHODS: Measurements were performed with regard to HU values of the cortex and papillae of 82 patients with unilateral nephrolithiasis and 81 patients in the control group at the level of the upper pole, middle region and lower pole of both kidneys. RESULTS: When the HU values obtained from the upper pole, middle region and lower pole of the kidney with calculi and unaffected kidney in patients with nephrolithiasis were compared with those for the control group, the difference among the groups were found to be significant (p<0.001). A comparison of the cortex and papillae densities of the affected and unaffected kidneys in patients with unilateral nephrolithiasis were compared with regard to the upper pole and middle region, no statistically significant difference was observed with regard to both the cortex and papillae densities of the upper pole, middle region. However, in those patients with calculi in the lower pole, the region with calculi has a higher papillae density as compared to the unaffected region. CONCLUSION: Both kidneys in patients with calculi have a comparatively high renal cortex and papillae densities. In the future, this information may be useful in predicting which patients may develop nephrolithiasis.

Role of preoperative plasma CA 15-3 and carcinoembryonic antigen levels in determining histopathologic conventional prognostic factors for breast cancer.

Breast cancer is one of the leading causes of cancer death among women all over the world, with about one million new breast cancer cases diagnosed per year. This large number of cases make the diagnosis, treatment, and determination of the factors affecting the survey extremely important. The aim of this study was to evaluate the importance of the preoperative plasma CA 15-3 and carcinoembryonic antigen (CEA) levels when determining the conventional histopathologic prognostic factors (tumor grade, lymphatic infiltration, stromal invasion, vessel invasion, tumor necrosis, elastosis, and number of positive lymph nodes in levels I and II). We believe that with this protocol doctors can add to their knowledge about the prognosis of patients. After examining the serum tumor marker levels and the histopathology results of 29 patients and submitting them to statistical calculations, we strongly believe that preoperative serum CA 15-3 levels can be taken into consideration when evaluating the prognosis because the CA 15-3 level is directly and positively correlated with the gold standard prognostic factor: the number of level I and II positive lymph nodes.

Paclitaxel and doxorubicin combination in the first-line treatment of metastatic breast cancer.

Anthracyclines and taxanes are currently the most effective drugs in the treatment of metastatic breast carcinoma. The aim of this study was to determine the efficacy and toxicity of paclitaxel and doxorubicin combination in the first-line treatment of metastatic breast cancer. Forty-five women with metastatic breast cancer were recruited in the study. Median age was 49 years (range, 33-70). Treatment protocol: doxorubicin (50 mg/m2/day, 30-min infusion) followed by paclitaxel (200 mg/m2/day, 3-hr infusion) every 3 weeks. Response rates included complete response in 13 (28.9%) patients and partial response in 19 (42.2%) patients, with an overall response rate of 71%. Five (11%) patients had stable disease and 8 (18%) patients had progressive disease. At a median follow-up of 19.7 months, median time to progression for all patients was 19.9 months (95% confidence interval, 12.8 to 27 months). Median overall survival time was 28.4 months. Grade 3-4 nausea/vomiting and hematological toxicities were observed in 12 (26%) and 6 (13.3%) patients, respectively. Cardiac toxicity was observed in 2 (4.4%) patients. In this trial, paclitaxel and doxorubicin combination was demonstrated to be a favorable and active regimen in the first-line treatment of metastatic breast cancer.

Neoadjuvant chemotherapy with taxotere-epirubicin-5-fluorouracil (TEF) in local-regionally advanced breast cancer: a preliminary report.

AIMS AND BACKGROUND: Sixty-three patients with local-regionally advanced breast cancer were treated with neoadjuvant chemotherapy consisting of docetaxel (Taxotere), epirubicin, and 5-fluorouracil (TEF). METHODS AND STUDY DESIGN: Preoperatively, patients received four cycles of Taxotere (80 mg/m2), epirubicin (60 mg/m2), and 5-fluorouracil (500 mg/m2), repeated every 21 days. Following completion of four cycles of chemotherapy, appropriate surgery was performed. After the surgery, patients received one cycle of the TEF chemotherapy regimen; following chemotherapy, radiotherapy was applied, and at the end two more cycles of TEF chemotherapy regimen were given. RESULTS: Sixty-three patients with locally advanced breast cancer were treated. Three patients were excluded from the study before the evaluation of response. Median age of the patients was 50 years (range, 25-77). Twenty-seven and 33 patients were premenopausal and postmenopausal, respectively. Thirty-nine patients were in stage IIIA and 21 in stage IIIB. Complete and partial responses were observed in 15 (25%) and 42 (70%) of the patients following four cycles of preoperative TEF chemotherapy regimen, respectively. Overall response was 95%, and primary lesion progressed only in 3 (5%) patients. The mean disease-free survival was 15.9 +/- 6.8 (range, 3.5-28) months and the mean overall survival was 18.6 +/- 7.2 (range, 5-30) months. The most frequent side effects were nausea-vomiting, mucositis, alopecia and leukopenia. CONCLUSIONS: TEF therapy is a treatment with a high overall response rate and toxicities similar to other taxotere combinations. A longer follow-up of patients is necessary for the determination of disease-free survival and overall survival.