Browsing by Subject "peel test"
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Item A Generalized Cohesive Zone Model of Peel Test for Pressure Sensitive Adhesives(2010-01-16) Zhang, LiangThe peel test is a commonly used testing method for adhesive strength evaluation. The test involves peeling a pressure sensitive tape away from a substrate and measuring the peel force that is applied to rupture the adhesive bond. In the present study, the mechanics of the peel test is analyzed based on a cohesive zone model. Cohesive failure is assumed to prevail in the vicinity of the peel front, that is, the adhesive fails not by debonding from the adherends but by splitting of the adhesive itself. Generally, the failure of the adhesive is accompanied with a process of cavitation and fibrillation. Therefore, the cohesive zone is modeled as a continuous fibrillated region. A Maxwell model is employed to characterize the viscoelastic behavior of the adhesive. The governing equation and boundary conditions that describe the mechanics of the peel test are derived. Numerical results are obtained under steady state conditions. The model predicts the peel force in terms of the peel rate, the peel angle, the nature of the adhesive, and the properties of the backing and the substrate. The traction distribution on the substrate surface is found to depend on various test parameters. Finally, finite element analysis is performed using the commercial software package ABAQUS. The results from FEA are compared with those from the mathematical method to evaluate the validity of the present model. The effective range of the present model is found to be related to the ratio of the critical fibril length to the extent of the cohesive zone. Given the nature of the adhesive as well as the properties of the backing and the substrate, the proposed model is able to predict the peel force and the traction distribution in terms of the peel rate and the peel angle, and thus provides a measure of the strength of the adhesive bond.Item Seal strength models for medical device trays(2009-05-15) Mays, Patricia FayeSeven empirical equations were developed for the prediction of seal strength for medical device trays. A new methodology was developed and used for identifying burst and peel locations and comparing burst pressure and peel force. Multiple linear regression was used to fit 76 models, selecting the best models based on the Akaike Information Criterion (AIC) and adjusted R2 (R2 adj) value of each model. The selected models have R2 adj and prediction R2 (R2 pred) values of .83 to .94. Factors investigated for the peel force response were sealing pressure (3 levels), dwell time (3 levels), sealing temperature (3 levels), and adhesive. Additional factors investigated for the burst pressure response were restraining plate gap, and tray volume, height, length-to-width ratio and area. Polyethylene terephthalate-glycol (PETG) trays with Tyvek 1073B lids and two popular water-based adhesives were used. Trays were selected to yield three levels of area and three levels of length-to-width ratio, defining nine package configurations. Packages for burst testing were sealed under a fractional factorial design with 27 treatments. Packages for peel testing were sealed under a 17-point face-centered central composite design. Packages were tested using peel testing following the ASTM F88-07 standard and restrained burst testing with three gap distances following the ASTM F2054-00 standard. All possible subsets of the factors were evaluated, with the best models selected based on AIC value. Equations were developed to predict peak and average peel force based on sealing process parameters (R2 pred =.94 and .92), burst pressure based on tray and sealing parameters and gap (R2 pred =.94), and four peel force responses based on burst pressure and gap (R2 pred =.83 to .86). Models were validated through cross-validation, using the prediction error sum of squares (PRESS) statistic. The R2 pred was calculated to estimate the predictive ability of each model.