Improving the Quality of Laminates in Liquid Composite Molding Using Magnetic Compaction: Experiments and Process Model

Despite the extensive use of liquid composite molding (LCM) processes such as wet lay-up vacuum bagging (WLVB) and vacuum assisted resin transfer molding (VARTM) in composite manufacturing, they have two major drawbacks. First, the fiber volume fraction of the composite parts made by LCM is lower than those made under an elevated pressure using either autoclave or hot press, leading to lower mechanical properties. Second, the process induced defects in LCM parts are quite high, which may significantly reduce the mechanical performance and environmental durability of composites. The focus of this dissertation is to tackle the important problems encountered with WLVB and VARTM to improve the quality of molded parts. The first part of this dissertation introduces a novel technique, magnet assisted composite manufacturing (MACM), to improve the quality of WLVB laminates. In this technique, the composite lay-up is sandwiched between a magnetic tool plate and a set of Neodymium-Iron-Boron (NdFeB) permanent magnets during cure. The details and effectiveness of MACM process are investigated by fabricating of E-glass/epoxy composite laminates with and without magnetic pressure and comparing their void content and morphology, fiber volume fraction, and mechanical properties. The results clearly show that the quality of composite laminates is significantly improved in the presence of magnetic consolidation pressure, where the fiber volume fraction increases by more than 50% to almost 30% and process-induced voids decrease to less than 3%. As a result, the flexural strength and modulus of the parts are enhanced by approximately 60% and 50% to ~245 MPa and ~10 GPa, respectively. The second part of the dissertation extends the application of the MACM technique to fabricate high-quality VARTM laminates. In VARTM, unlike the WLVB process, the preform impregnation takes place under vacuum, which results in different mechanisms of void formation and different ranges of fiber content. Thus, enhancing VARTM is quite different than enhancing the WLVB process which provides the motivation to investigate the effectiveness of utilizing MACM in VARTM. In this regard, thin (i.e. 6-ply), as well as moderately thick (i.e. 12- and 18-ply) E-glass/epoxy laminates are fabricated by applying MACM either before or after infusion. The results prove the effectiveness of MACM in fabricating high-quality VARTM laminates where a fiber volume fraction of more than 50% and void content of less than 1% is achieved. In addition, a transient magnetic consolidation model is developed, predicting the final thickness and fiber volume fraction of the VARTM/MACM parts. The third part of this dissertation introduces a novel technique of compacting dry fibrous reinforcement to control the resin flow rate, thus eliminating the void formation in VARTM parts. In this technique, the fibrous preform is compacted by either stationary or moving magnets prior to resin infusion. As a result, the pore size between the fabric layers and permeability are reduced, and the filling rate of resin into preform decreases. The results show that in the absence of magnetic pressure, the void content could be up to 5.7%, much higher than 0.1-0.8% voids in the laminates made by 0.2 MPa magnetic compaction. In addition, moving magnets with a smaller footprint over a larger vacuum bag surface is a feasible approach to apply compaction pressure on medium to large parts, thus dramatically decreasing their void content to below 1%

EFFECT OF AUTOCLAVE CURE PRESSURE ON MECHANICAL PROPERTIES AND VOID CHARACTERISTICS OF COMPOSITE LAMINATES

International audienceAutoclave curing is a commonly used fabrication process for high-performance structural composite laminates used in aerospace industry. During the manufacturing, a variety of process parameters such as the temperature and the pressure in the autoclave influence the formation of voids throughout the laminate. In particular, the magnitude of autoclave pressure determines the final fiber volume fraction, overall void content, and mechanical properties, including flexural strength and modulus. In this study, a number of composite laminates made of IM7/EX-1522, a carbon fiber reinforced epoxy prepreg, are produced by autoclave curing. The influence of different pressures on flexural properties of composite laminate is examined. In addition, void volume fraction as well as shape and size distributions of voids are presented. The experimental results have shown that increasing consolidation pressure during cure alone may not increase all the mechanical properties. Flexural modulus is found to be higher at higher consolidation pressure which is attributed to the higher fiber volume fraction. Unlike the flexural modulus, the flexural strength is significantly affected by the location, size, and shape of the voids. If the magnitude of cure pressure is not chosen properly, elongated voids may form at the fiber-matrix and could lead to considerable reduction of interfacial strength of the composites

Enumeration of leukocyte infiltration in solid tumors by confocal laser scanning microscopy

BACKGROUND: Leukocytes commonly infiltrate solid tumors, and have been implicated in the mechanism of spontaneous regression in some cancers. Conventional techniques for the quantitative estimation of leukocyte infiltrates in tumors rely on light microscopy of immunostained thin tissue sections, in which an arbitrary assessment (based on low, medium or high levels of infiltration) of antigen density is made by the pathologist. These estimates are relatively subjective and often require the opinion of a second pathologist. In addition, since thin tissue sections are cut, no data regarding the three-dimensional distribution of antigen can be obtained. RESULTS: To overcome these problems, we have designed a method to enumerate leukocyte infiltration into tumors, using confocal laser scanning microscopy of fluorescently immunostained leukocytes in thick tissue sections. Using image analysis software, a threshold was applied to eliminate unstained tissue and residual noise. The total antigen volume in the scanned tissue was calculated and divided by the mean cell volume (calculated by "seeding" ten individual cells) to obtain the cell count. Using this method, we compared the calculated leukocyte counts with those obtained manually by ten laboratory personnel. There was no significant difference (P > 0.05) between the cell counts obtained by either method. We then compared leukocyte infiltration into seven tumors and matched non-malignant tissue obtained from the periphery of the resected tissue. There was a significant increase in the infiltration of all leukocyte subsets into the tumors compared to minimal numbers in the non-malignant tissue. CONCLUSION: From these results we conclude that this method may be of considerable use for the enumeration of cells in tissues. Furthermore, since it can be performed by laboratory technical staff, less time input is required by the pathologist in assessing the degree of leukocyte infiltration into tumors

Losartan enhances the suppressive effect of pirfenidone on the bleomycin-induced epithelial-mesenchymal transition and oxidative stress in A549 cell line

Objective(s): Idiopathic pulmonary fibrosis (IPF) is a fatal lung disease. Despite the promising anti-fibrotic effect, the toleration of pirfenidone (PFD) by the patients in full dose is low. Combination therapy is a method for enhancing the therapeutic efficiency of PFD and decreasing its dose. Therefore, the present study evaluated the effect of a combination of losartan (LOS) and PFD on oxidative stress parameters and the epithelial-mesenchymal transition (EMT) process induced by bleomycin (BLM) in human lung adenocarcinoma A549 cells. Materials and Methods: The non-toxic concentrations of BLM, LOS, and PFD were assessed by the MTT assay. Malondialdehyde (MDA) and anti-oxidant enzyme activity including catalase (CAT) and superoxide dismutase (SOD) were assessed after co-treatment. Migration and western blot assays were used to evaluate EMT in BLM-exposed A549 after single or combined treatments. Results: The combination treatment exhibited a remarkable decrease in cellular migration compared with both single and BLM-exposed groups. Furthermore, the combination treatment significantly improved cellular anti-oxidant markers compared with the BLM-treated group. Moreover, combined therapy markedly increased epithelial markers while decreasing mesenchymal markers. Conclusion: This in vitro study revealed that the combination of PFD with LOS might be more protective in pulmonary fibrosis (PF) than single therapy because of its greater efficacy in regulating the EMT process and oxidative stress. The current results might offer a promising therapeutic strategy for the future clinical therapy of lung fibrosis

INVESTIGATION THE ROLE OF MEPXH1 (HIS139ARG) POLYMORPHISM ON NUMBER OF EXACERBATIONS AND DISEASE SEVERITY IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE IN A SMOKER POPULATION

The purpose of this study was to examine investigation the role of mEPXH1 (His139Arg) polymorphisms on number of exacerbations and disease severity in chronic obstructive pulmonary disease in a smoker population. Chronic obstructive pulmonary disease (COPD) has become the fourth most common single cause of morbidity, and its prevalence is increasing worldwide. It is a syndrome composed of chronic bronchitis, small airways disease (bronchiolitis), and emphysema, in varying proportions between affected individuals. The study was performed cohort and prospectively. The population consist of 213 patients with COPD disease. Genotyping of mEPXH1 was performed using multiplex PCR. Data analysis included, Pearson’s r correlations, regression analysis, ANOVA analyses, Tukey, test for comparison and SPSS software (package of Spss / pc + + ver18). The results showed that there is not relationship between polymorphisms of mEPXH1 and number of exacerbations. According the results, there is not significant relationship between polymorphisms of mEPXH1 and disease severity. Also there is not significant relationship between mEPXH1 and disease in COPD patients on basis parameters of spirometery and oxidative stress in COPD patients

CalDAG-GEFI deficiency protects mice from FcγRIIa-mediated thrombotic thrombocytopenia induced by CD40L and β2GPI immune complexes

Platelet activation via the Fcγ receptor IIa (FcγRIIa) is implicated in the pathogenesis of immune complex (IC)-mediated thrombocytopenia and thrombosis (ITT). We previously showed that ICs composed of antigen and antibodies targeting CD40 ligand (CD40L) or β2 Glycoprotein I (β2GPI) induce ITT in mice transgenic for human FcγRIIa (hFcR) but not wild-type controls (which lack FcγRIIa). Here we evaluated the contribution of the guanine nucleotide exchange factor, CalDAG-GEFI, and P2Y12, key regulators of Rap1 signaling in platelets, to ITT induced by these clinically relevant ICs

Manufacturing silk/epoxy composite laminates : challenges and opportunities

Presented at the 34th International Conference of the Polymer Processing Society, May 24, 2018.Application of natural fibers in polymer composites has been gaining popularity in several industries pursuing environmentally friendly products. Among the natural fibers with proven potential applications, silk fibers have recently received considerable attention from researchers. Silk fibers provide higher mechanical properties compared to other commonly used natural fibers such as sisal, jute, and hemp. Silk may also exhibit comparable specific mechanical properties to glass fibers. However, silk composite laminates are rarely used in commercial products due to a number of fabrication challenges. This paper investigates such challenges for silk/epoxy laminates, especially issues related to manufacturing and preform architecture. First, challenges arising from preform architecture (i.e., random and woven preforms) are presented. Unlike glass fibers for which random mats are easier to manipulate, handling random silk preform proves to be more challenging, particularly compared to woven silk fabrics. The random silk/epoxy laminates show higher thickness variation and lower compaction, yielding lower fiber content. Second, fabrication of laminates by vacuum bag/wet lay-up and vacuum assisted resin transfer molding (VARTM) processes are presented. VARTM is found to be more appropriate for silk/epoxy laminate fabrication, as it allows a uniform impregnation of the silk preform, yielding higher part quality and limited void formation. Moreover, applying 0.21 MPa (30 psi) external pressure to the VARTM laminates allows to increase the fiber content of both random and woven silk/epoxy laminates from ~17 and ~30% to ~21 and ~33%, respectively. In contrast, wetting of silk preform during wet lay-up process, which is operator dependent, is difficult to achieve; and the produced laminates have high void content. Furthermore, SEM images show a weak silk/epoxy adhesion in laminates fabricated without external pressure. Finally, the mechanical performance of these laminates is assessed. The woven silk/epoxy laminates fabricated by pressurized VARTM exhibits the highest improvement in the specific flexural strength and modulus over pristine epoxy with 30 and 65% increase, respectively.YesPeer reviewed for the Proceedings of the 34th International Conference of the Polymer Processing Society, Taipei, Taiwan, May 21st-25th 2018