15,397,112 research outputs found
Analysis of contact area in a continuous application-and-peel test method for prepreg tack
No full textThe relationship between prepreg tack and the degree of intimate contact (DoIC) between prepreg and a rigid substrate was explored in the context of a continuous application-and-peel test method. Tack for a unidirectional prepreg tape was characterised for different surface combinations and varying test parameters (material feed rate, temperature) at a constant compaction pressure. Application of the prepreg to a transparent rigid substrate (glass), was carried out at matching test conditions to the prepreg tack measurements. Optical microscopy was utilised to acquire images of the contact area at the prepreg-glass interface. Image analysis of the micrographs enabled quantification of the contact area. The time- and temperature-dependent viscoelastic behaviour of the resin was explored directly on the prepreg using oscillatory parallel plate rheometry, and time-temperature superposition was applied to construct both tack and DoIC master curves. The shifted DoIC data showed that true contact area increases with decreasing shifted feed rates, until maximum contact area is achieved. Similarly, tack increases with decreasing shifted feed rates. However, at a critical feed rate, the bond failure mechanism switches from adhesive to cohesive failure. In cohesive failure, tack decreases with decreasing feed rate despite the high levels of DoIC
Tack coat performance and materials study
No full text"June 2017."; "FHWA/OH-2017-33"--Technical report documentation page.; Includes bibliographical references (pages 23-25 of Final report).; Final report;; Sponsoring agency: Ohio Department of Transportation; State Job NUmber 135097 [SJN 135158 on Technical report documentation page is an error].Final report (106 pages in various pagings : illustrations (chiefly color)) -- [Fact sheet]: Tack coat strategies: field performance and life cycle cost (3 pages : color illustrations).A good bond provided by a tack coat can improve performance of asphalt overlays. The objectives of this research were: (1) develop a method for testing the bond between pavement layers; (2) evaluate the bond performance and predict long-term performance of different tack coat strategies; (3) assess the minimum bond to achieve acceptable performance; and (4) evaluate the cost effectiveness of different tack coat strategies. Field test sections were constructed considering surface type, tack type, tack rate, and application method. Core bond performance, initial and after 8-months, was tested in the lab with an interface shear strength tester. Tack type, application method, and bond age were statistically significant variables. Trackless tack had the highest bond performance. High performance was also achieved by SS-1H placed with a distributor, and by notack samples. The rubberized tack and SS-1H placed with a spray paver had the lowest bond performance; however, after eight months, bond performance for these sections doubled and was well acceptable. Performance was predicted considering reflection cracking, rutting, and fatigue cracking. Generally, higher bond strength resulted in longer service life; however, on the milled HMA sections, the optimal performance was achieved at a partially bonded condition. The differences among pavement life-cycle costs for the different materials and methods were small, between 2 and 6 percent of the overall project cost. The shear bond strength test is recommended to evaluate field bond performance. A tack coat construction specification, with a minimum initial bond strength of 70 psi, may be considered for exploratory work
Experimental determination and control of prepreg tack for automated manufacture
No full textThe automated tape laying (ATL) process has been examined and found to be sensitive to tack and stiffness properties of the prepreg material being laid. A comparison of existing aerospace and newly developed ATL prepreg tapes has revealed significant differences in tack response to temperature and feedrate. Examination of constituent resin rheology has found that tack, and the two observed failure modes, are somewhat dependent upon viscoelastic stiffness. Observation of temperature and feedrate response revealed a time–temperature superposition relationship. The Williams–Landel–Ferry equation was utilised to make predictions of the temperature response based on the feedrate response. Tack levels were stabilised over the feedrate range by making temperature adjustments. Results from the peel test, where mould conditions at lay-up were recreated, were found transferable to the ATL, where a suitable lay-up feedrate under ambient conditions was predicted
The experimental determination of prepreg tack and dynamic stiffness
No full textA new peel test has been developed which quantifies the tack and dynamic stiffness of uncured prepreg. The test is designed to simulate the automated tape lay-up (ATL) and automated fibre placement (AFP) processes. It includes a pressure controlled application stage, where contact time is inversely proportional to peel rate. The use of a thin film allows stiffness to be isolated from peel resistance in a continuous two stage test. A repeatability study revealed consistent results with 16% standard deviation. Tack and stiffness variability has been observed across roll width and between faces in commercial hand lay-up prepregs. The overall tack and stiffness values for commercial hand lay-up prepregs were found to be inconsistent with the levels specified by manufacturers. A temperature increase revealed inconsistent effects on tack between materials. The contradictory results were rationalised by observing failure modes. The two failure modes observed appeared equivalent to those found in pressure sensitive adhesive (PSA) peel. The shear storage modulus of the prepreg resin was compared to the PSA Dahlquist criterion and found to support the principle of contact efficiency. However, the actual value for the criterion is expected to be a function of prepreg specific conditions such as resin content, fibre distribution and surface pattern
North Korean Economy: A Historical Assessment
No full textPart Five (Chapter 16)presents a historical review of North Korea`s economic system and policies together with its performances. Analyzing the causes of its economic plight in the 1990s, the authors also suggest a direction for the reforms required to improve its economic situation.PartⅤ. North Korean Economy
16. North Korean Economy: A Historical Assessment, Hong-Tack Chun and Jin ParkTRU
Clinical trial design in adult reflux disease: a methodological workshop
No full textBackground: The development of well-tolerated acid suppressant drugs has stimulated substantial growth in the number of trials assessing therapy options for gastro-oesophageal reflux disease (GERD). Aim: To develop consensus statements to inform clinical trial design in adult patients with GERD. Methods: Draft statements were developed employing a systematic literature review. A modified Delphi process including three rounds of voting was used to reach consensus. Between voting, statements were revised based on feedback from the Working Group and additional literature reviews. The final vote was at a face-to-face meeting that included discussion time. Voting was conducted using a six-point scale. Results: At the last vote, 93% of the final 102 statements achieved consensus (defined a priori as being supported by ‡75% of the votes). The Working Group strongly supported the development of validated patientreported outcome instruments. Symptom assessments carried out by the investigator were considered unacceptable. There was agreement that exclusion from clinical trials should be minimized to improve generalizability, that prospective evaluation ideally requires electronic timed ⁄ dated methods and that endoscopists should be blinded to patient symptom status. Conclusions: Implementation of the consensus statements will improve the quality and comparability of trials, and make them compatible with regulatory requirements.J . Dent, P. J . Kahrilas, N. Vakil, S. Veldhuyzen Van Zanten, P. Bytzer, B. Delaney, K. Haruma, J. Hatlebakk, E. McColl, P. Moayyedi, V. Stanghellini, J . Tack and M. Vaezihttp://www3.interscience.wiley.com/journal/120088380/issu
Gastroparesis: separate entity or just a part of dyspepsia?
No full textGastroparesis is defined by the presence of delayed gastric emptying (GE) in the absence of mechanical obstruction. Symptoms that have been attributed to gastroparesis include postprandial fullness, early satiation nausea and vomiting. Gastroprokinetic drugs are the preferred treatment option. A number of problems with the concept of gastroparesis have been identified recently. Major overlap exists with the symptom complex of the functional dyspepsia subtype of postprandial distress syndrome. The distinguishing feature of gastroparesis is delayed GE, but the correlation between delayed emptying and symptom pattern or severity in gastroparesis is modest and the stability of delayed emptying over time is poor. Other pathophysiological mechanisms such as hypersensitivity or impaired accommodation may also underlie symptoms in patients with gastroparesis. Moreover, symptomatic response to prokinetic therapy is variable and cannot be predicted based on the degree of enhancing GE. A number of approaches have been proposed to increase clinical usefulness of a diagnosis of gastroparesis, including a higher threshold of abnormal emptying and selection of patients with a specific symptom pattern more likely to be associated with delayed emptying
felt tack
No full textfeltsee SWAB JAN 1976Used I and SupNot usedNot usedsee SWABFelt tack appears to have the same meaning as "felt tins" in DNE-Su
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