bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fracture mechanics parameters for polystyrene under high speed impact
Authors: Cook D. G. , Rudin A. , Plumtree A. 
Published: December 2004

AbstractA series of commercial polystyrenes was tested using an instrumented impact tester to determine the fracture toughness Kc and critical strain energy release rate Gc. Over the range of Mw, 201,000 to 336,000, Kc increased from 1.38 MN/m3/2 to 1.76 MN/m3/2and Gc from 0.92 kJ/m2 to 1.60 kJ/m2. A linear correlation for Kc and Gc was seen with melt index, and an inverse relationship was obtained against molecular weight. Examination of the fracture surfaces revealed the presence of crack growth bands corresponding to the crack tip plastic zone size. It is suggested that these bands are the consequence of variations in crack growth along crazes that form in the crack tip stress field. As the crack propagates, the stress is relaxed locally, decreasing the growth rate allowing a new bundle of crazes to nucleate along which the crack advances. The spacing of these bands corresponds to the craze length formed in the plastic zone, and the band spacing increases with molecular weight.
Mathematical modeling of the in‐mold coating process
Authors: Castro J. M. , Griffith R. M. 
Published: December 2004

AbstractFiber glass reinforced polyester parts compression molded from sheet molding compound (SMC) are prone to such surface inconsistencies as porosity and sinks. Even though it appears that some of these defects could be eliminated by techniques such as vacuum molding, the resulting surface, with current technology, is not yet consistently up to automotive standards for exterior body panels. In‐mold coating (IMC) of SMC, is designed to fill porosity, reduce sinks, and furnish a primer‐like coating, thus upgrading the part surface to automotive standards. As a consequence, IMC is generally an integral part of the molding cycle when producing compression molded SMC exterior automotive body panels. Most commonly, in‐mold coating is injected after opening the press slightly so as to separate the mold cavity and the exterior surface of the part to make room for the coating. A second approach is to let the hydraulic pressure of the injected IMC open the mold. Here, we present a mathematical model of the process and show application in predicting injection pressures, fill times, and filling patterns. A comparison with experimental results is also presented. Cycle times required for IMC injection methods is also discussed.
Structural heterogeneity in epoxies
Authors: Wu Wen‐Li , Hu Jiann‐Tsun , Hunston Donald L. 
Published: December 2004

AbstractThe effects of different cure procedures on the structure and properties of epoxy samples made from diglycidyl ether of bisphenol A (DGEBA) and mixtures of two linear aliphatic diamines were studied. The elastic modulus, fracture toughness, impact resistance, and glass transition temperature were determined for various cure schemes. The morphologies of the cured resins were characterized with small angle X‐ray scattering. The results show that samples with the same average morphology (molecular network structure) have similar elastic moduli and glass transition temperatures. If some heterogeneity is introduced in the molecular network structure without changing the average structure, however, the experiments indicate that the toughness can be increased without significantly sacrificing other properties.
Optimization of injection molding design. Part II: Molding conditions optimization
Authors: Pandelidis Ioannis , Zou Qin 
Published: December 2004

AbstractThe quality of an injection molded part is affected by many factors. These include geometric parameters associated with the mold design and the cooling system design as well as process parameters such as the molding conditions during the filling phase. In the companion paper, the problem of automatic optimization of gate location was addressed. In this paper, a methodology for molding condition optimization is presented. The optimization problem can be broken into three parts. An approximate feasible molding space (AFMS) is first determined to constrain the search space for the optimization algorithm. Quality is quantified as a function of flow simulation outputs and constitutes the objective function that must be minimized. The resulting optimization is solved by iterative search in the constrained space based on numerical optimization algorithms. The proposed methodology is not dependent on any particular simulation package and may be applied for any thermoplastic material and any complex mold geometry.
Functionalization of ethylene‐propylene rubber via melt mixing
Authors: Wu C. H. , Su A. C. 
Published: December 2004

AbstractGrafting of maleic anhydride (MAH) onto ethylene‐propylene rubber (EPR) of apppoximately unitary ethylene/propylene molar ratio was performed by melt mixing in a laboratory‐scale internal mixer with the addition of dicumyl peroxide (DCP) as an initiator. Concurrent with the graft reaction, the simultaneous presence of DCP and MAH enhanced the cross‐linking of EPR chains as suggested by the emergence of a cure peak in the mixing torque, curve and supported by dynamic rheological evidence; the DCP‐induced chain scission, however, remained important. The height of the cure peak increased consistently with the amounts of DCP and MAH in the reaction mixture. At the end of ca. 30 min of melt mixing, the gel content (determined via xylene extraction) of the functionalized EPR increased with the height of cure peak but then levelled off in the vicinity of ca. 50 wt%. The limited gel content was attributed to the competition from DCP‐initiated scission reaction. This competition resulted in a wide distribution of chain connectivity, ranging from highly degraded short chains to partially cross‐linked chains. At low DCP levels, the extent of grafting (estimated by means of Fourier‐transform infrared spectroscopy) increased with the MAH content and then remained at a plateau value; at higher DCP levels, the plateau appeared to have already been reached even at the lowest MAH content (i.e., 0.5 phr) here. The limited extent of grafting was attributed to the immiscible nature and the low diffusion rate of MAH in EPR.
The interparticulate friction behavior of acetal copolymer pellets with bilobal and trilobal cross‐sections
Authors: Liu Chia‐Ying , O'Brien Keith T. 
Published: December 2004

AbstractThe interparticulate friction coefficient has been measured for a range of pellet cross‐sections. This measurement is postulated as representing the integrity of the solid bed in plasticating extrusion, reciprocating‐screw injection molding and extrusion blow molding. The value of the interparticulate friction coefficient has been found to be consistently greater for profiled pellet cross‐sections such as bilobal and trilobal than for conventional pellets with circular cross‐sections. It is postulated that this result means that solids beds formed from pellets with profiled cross‐sections are less likely to fracture, or break‐up, than are solids beds formed with conventional pellets, during plasticating extrusion, reciprocating‐screw injection molding and extrusion blow molding. It is further postulated that this will result in surge inhibition, and allow the manufacturing units to run faster with fewer operational problems. The effects of normal load, pellet geometry, polymer molecular weight and agitation of the bed are also presented. In addition to the measurement of the interparticulate friction coefficients, the manufacturing procedures for profiled pellets are explained.
Prediction of gel‐time in the cure of unsaturated polyester resins: Phenomenological modeling vs. statistical analysis
Authors: Muzumdar Shailesh V. , Lee L. James 
Published: December 2004

AbstractA series of kinetic and rheological measurements were carried out using a differential scanning calorimeter (DSC) and a Rheometrics Dynamic Analyzer (RDA). The effects of temperature, inhibitor level, initiator level, and initiator type on the curing of unsaturated polyester resins were investigated. Two models based on the free radical polymerization mechanism were developed for predicting the time to reach liquid‐solid transition. These models adapted a concept that gelation occurred at a critical radical concentration. The applicability of these models was compared to that of a statistical analysis.
Stiffness of polyoxymethylene whiskers/polyoxymethylene resin composite films
Authors: Zahran R. R. 
Published: December 2004

AbstractThis paper presents a refinement of an erroneous, recently published analysis of the mechanical properties of polyoxymethylene (POM) whisker/POM resin composite system. Furthermore, it extends the applicability of the molecular composite model to isotropic POM resins. It is shown that using the Halpin‐Tsai equation, coupled with the laminate theory, is highly superior to using the Nielsen‐generalized Halpin‐Tsai equation for predicting the modulus of the whisker/resin system. The comparison between the experimental tensile modulus data and the predicted results, as functions of the whisker volume content, yields a good agreement to better than 15%.
Transcrystallinity phenomena in fiber‐reinforced polypropylene. II: Morphology, thermal and mechanical properties relationships
Authors: Avella Maurizio , Martuscelli Ezio , Pascucci Beniamino , Raimo Maria 
Published: December 2004

AbstractThe effect of short‐length carbon and Kevlar fibers on the crystallization of isotactic polypropylene (iPP) in composites prepared by compression molding has been investigated. The tendency of carbon and Kevlar fibers to nucleate the iPP during isothermal and nonisothermal crystallization has been evaluated by differential scanning calorimetry. The influence of different thermal histories used to prepare the unreinforced and reinforced samples on the crystallization parameters of iPP was examined. In addition, the tensile behavior was related to the resulting morphologies of the samples. It was observed that the crystallinity content, obtained by using different thermal treatments (slowly cooling or quenching), gives rise to different morphologies by influencing the mechanical behavior of materials as well. Moreover, the composites obtained by slow cooling seem to present a better fibber/matrix adhesion then that found in quenched samples. Possible underlying microstructures, which can explain the properties and the morphological characteristics, are also discussed.
The grafting of maleic anhydride on high density polyethylene in an extruder
Authors: Ganzeveld K. J. , Janssen L. P. B. M. 
Published: December 2004

AbstractThe grafting of maleic anhydride (MAH) on high density polyethylene in a counter‐rotating twin screw extruder has been studied. As the reaction kinetics appear to be affected by mass transfer, good micro mixing in the extruder is important. Due to the competing mechanisms of increasing mixing and decreasing residence times at increasing screw speed, and due to the complicated reaction scheme, various non‐linearities exist that are prohibitive for simple optimization rules. The interaction diagram presented in this paper for a twin screw extruder as a MAH grafting reactor can be used for better understanding of the influence of the extruder parameters on the reaction process.
Optimization of stabilizer formulations for polyolefin processing
Authors: Pearson L. Timothy , Sousa Marcia 
Published: December 2004

AbstractAn approach to formulation is presented that is based on a statistical experimental design package for use on a personal computer. The total level of phosphite + hindered phenol, and the ratio of phosphite to hindered phenol are used as experimental variables. The approach was tested on extrusions of polypropylene using melt flow retention and yellowness index as observed variables. A quadratic model gave a satisfactory fit to the data for both variables. Contour plots are presented of the performance of the systems for two commercially available hindered phenols and two polypropylene samples. The largest difference between the resins is in the degree of color generation on extrusion. For both hindered phenols, a resin made using “3rd generation” or “high activity” catalyst gave lowest color development on extrusion. There were also small differences in the response of the melt flow of the resins to phosphite level.
The kinetics of photo‐oxidation of low‐density polyethylene films
Authors: Carvalho M. E. S. , Cruz‐Pinto J. J. C. 
Published: December 2004

AbstractThe kinetics of the accelerated photo‐oxidation of low‐density polyethylene (LDPE) films has been studied within a range of temperatures, using an ultraviolet radiation enclosure. A simple, lumped parameter, kinetic model was developed to interpret the results of measurements of carbonyl and hydroperoxide absorbances as functions of time; the model predicts, with reasonable accuracy, the general experimental behavior and also that both the formation of hydroperoxides and carbonyl Norrish‐I reactions are important initiation steps. Slightly more complex models may thus have the potential of interpreting other fine details of the degradation behavior, namely the generation of other chemical species and the chain scission and cross‐linking processes, which are directly related to changes in the mechanical properties.
Ultrasonic welding using tie‐layer materials. part II: Factors affecting the lap‐shear strength of ultrasonic welds
Authors: Ramarathnam G. , North T. H. , Woodhams R. T. 
Published: December 2004

AbstractThe influence of tie‐layer Melt Flow Index on the lap‐shear strength of ultrasonic welds in oriented polypropylene (OPP) has been evaluated. The tie‐layer Melt Flow Index was varied from 0.03 dg/min to 2600 dg/min; the highest lap‐shear strength properties were obtained using tie‐layers that had melt flow index values between 30 and 100 dg/min. When using low Melt Flow Index tie‐layers, hot spot formation and concomitant changes in fusion zone and heat‐affected‐zone dimensions produced stress concentrations that promoted failure in oriented polypropylene material away from the bondline region. When very high Melt Flow Index (2600 dg/min) tie‐layers were used, the mode of failure during lap‐shear testing was a mix of cohesive, in oriented polypropylene, and adhesive failure. The molecular weight of material at the bondline was not markedly affected by the thermal cycle produced during ultrasonic welding. Only the flash ejected when using low Melt Flow Index tie‐layers exhibited any evidence of degradation; it is suggested that the ejected flash may have been degraded because of a combination of thermal, cavitation, and thermo‐oxidative processes.
A study of the residual microstress at the matrix interface in filled epoxy resins
Authors: Wang Hong‐Bing , Li Shan‐Jun , Zhou Hong‐Wei , Yu Tong‐Yin , Jin Xiao‐Wei 
Published: December 2004

AbstractUsing the technique of photoelasticity, we have studied in detail the magnitude of the residual microstress at the matrix interface between epoxy resin and rubber particles or glass beads. A spheric stress‐optic equation applicable to these composites was derived. The photoelastic figures induced by the interfacial residual microstresses and the factors affecting the intensity of light are discussed. The experimental results show that the residual microstresses at the matrix interface are independent of the particle size of rubbers or glass beads, but depend on the nature of fillers, which have different thermal expansion coefficients and mechanical properties. Thermal history and interfacial chemical bonding of filled epoxy resins have distinct effects on the residual interfacial microstresses and the matrix internal stresses.
Thermal shock resistance of flat plastic integrated circuit packages
Authors: Kojima Yoshitsugu , Ohta Takashi , Matsushita Mitsumasa , Takahara Minoru , Kurauchi Toshio 
Published: December 2004

AbstractFlat packages (FPs) were formed from epoxy molding compounds with various physical properties using a transfer molding machine. The compounds were prepared by changing kinds and amounts of additives and addition methods. The thermal shock test was carried out by the following procedures. The plastic package was soaked alternately in liquid nitrogen (−196°) and in liquid solder (200°) in the cycle of 140s. The median life to crack initiation was defined to be the cycles when half of the specimens exhibited crack initiation. According to linear fracture mechanics, the following expression was obtained relating the median life N, thermal stress σt, and strength σb; N = C/σ·(σb/σt)m. We found the linear relation between logarithm of Nσ and logarithm of σb/σt for various packages, and estimated the values of C and m as 5 × 104 MPa2 and 5.5, respectively. The value of m was the same as that obtained for a dual‐in‐line package.
Computer simulation of thermoforming in complex shapes
Authors: Kouba K. , Bartos O. , Vlachopoulos J. 
Published: December 2004

AbstractA finite element analysis of thermoforming based on the thin membrane approximation is presented. Triangular elements with adaptive mesh refinement are used to describe deformed shapes in complex geometries. Viscoelastic effects are assumed to be negligible, and Ogden's model is used to express the material response. The results are in good agreement with previous simulations and some experimental data available in the literature. The combination of adaptive mesh refinement near corners and edges, inclusion of slip or no‐slip conditions as required on mold walls, and an efficient equation solver allow simulation of thermoforming in complex geometrical shapes at reasonable computer times on a personal computer.
Cure of epoxy resins containing epoxidized polyols
Authors: Podgaiz P. , Riccardi C. C. , Williams R. J. J. 
Published: December 2004

AbstractA commercial epoxy resin, consisting of a mixture of diepoxides based on diglycidyl ether of bisphenol‐A (DGEBA) and containing an epoxidized polypropylene glycol as reactive diluent, was characterized by 1HNMR, FTIR, SEC, and chemical analysis. The kinetics of the cure with ethylenediamine (EDA) was catalyzed by the (OH) groups present in a large amount in the commercial formulation. A second order kinetic behavior gave an accurate fitting of results obtained by different experimental techniques (DSC in dynamic and isothermal modes and SEC in the pregel stage). The activation energy was E = 59.1 kJ/mol (14.1 kcal/mol), in very close agreement with values reported for the catalytic mechanism of the DGEBA‐EDA polymerization. From the gel conversion and the critical stoichiometric ratio for samples containing an epoxy excess it was found that the average functionality of epoxidized species was f = 1.58.
Rheology and morphology of some thermoplastic blends with a liquid crystalline copolyester
Authors: Ajji A. , Gignac P. A. 
Published: December 2004

AbstractLiquid crystalline polymers (LCPs) are known for their high performance properties. However, owing to their high cost, research efforts are much oriented to their use as reinforcements for different thermoplastics. In this study, we investigated the morphology, mechanical and dynamic rheological properties of blends of a 60/40 para hydroxybenzoic acid–ethylene terephthalate copolyester LCP (PHB/PET) with poly(butylene terephthalate) (PBT), poly(hexamethylene terphthalate) (PHMT), and polycarbonate (PC). Addition of up to 30 wt% of LCP to the different thermoplastics was performed in a Haake Rheomix mixer at 300°C. The dynamic rheological properties of the blends showed significant changes upon the addition of LCP, but no improvement in the mechanical properties was observed. The rheological properties of the blends below the nematic transition temperature of the LCP (210°C) were similar to those of solid filled thermoplastics. At 270°C, at which the LCP is in the nematic phase, the viscosity of LCP blends with PC blends decreased, whereas that obtained with PBT blends was increased. This is interpreted as being due to the differences in viscosity and interfacial tension between the components and to a possible reaction between the LCP and the thermoplastics.
Kinetic model for the curing reaction of a tetraglycidyl diamino diphenyl methane/diamino diphenyl sulfone (TGDDM/DDS) epoxy resin system
Authors: Lee Sung‐Nung , Chiu Ming‐Tsung , Lin Ho‐Sheng 
Published: December 2004

AbstractA kinetic model based on reaction mechanisms was proposed for the description of the curing behavior of a TGDDM/DDS resin system. The characteristic of this model is the separation of the non‐autocatalytic part from the autocatalytic part of the reaction, so the model can match the well‐established pseudo second order reaction mechanism, as proposed by many other studies about the epoxide/amine reaction. The present model was compared with two other widely used models for the autocatalytic curing behavior of epoxide/amine system, i.e., an equation based on a single rate constant and another based on pure phenomenological analysis, by using DSC data. It was found that the reaction rate calculated from this new model can fit the DSC empirical result much better than those calculated from the other two models. Parallel studies on some other resins, such as the DGEBA/m‐PDA system, also proved the superiority of this kinetic model. Results have revealed that the new model was valid for most of the epoxide/1o‐amine systems studied. A discrepancy did appear as the epoxide/amine molar ratio and/or the isothermal curing temperature reached certain limits, owing to the occurrence of side reactions.
The effects of thermomechanical coupling on the cold drawing process of glassy polymers
Authors: Boyce M. C. , Montagut E. L. , Argon A. S. 
Published: December 2004

AbstractThe source and the effects of strain‐induced heating on the stress‐strain behavior and corresponding cold drawing process of glassy polymers are investigated. The nature of dissipative and stored components of work are discussed where only 50 to 80% of the mechanical work of glassy polymers has been found to be dissipative. This phenomenon is demonstrated to be well‐modeled by considering a portion of the work to be stored as strain‐induced molecular orientation in the polymer that evokes a back stress tensor. The results of the modeling are found to be consistent with experimental measurements reported in the literature. The constitutive and corresponding heat generation model are used in fully thermomechanically coupled finite element analysis of the cold drawing of glassy polymers. The influence of applied elongation rate on the resulting temperature rise, heat transfer, thermal softening, and fiber geometry are presented, together with a full complement of the deformation field parameters related to the propagating shoulders of the drawn neck.
Influence of thickness and processing history on fatigue fracture of nylon 66. Part II: Crack tip morphology
Authors: Wyzgoski Michael G. , Novak Glen E. 
Published: December 2004

AbstractFatigue crack propagation rates in injection molded nylon 66 were previously shown to be strongly affected by prior processing history. To provide a physical basis for the observed acceleration in crack growth rates, microtomed sections were cut through the tips of stable fatigue cracks and examined by optical microscopy. A reduction in spherulite size occurs with reprocessing along with an accompanying decrease in the amount of deformation at the crack tip. For the initially processed nylon 66 this deformation consists of a vast array of independently initiated craze‐like zones. Patchy type regions observed on the fatigue fracture surface are similar in size to the initially formed crazed zones. Crack advance occurs by the breakdown and coalescence of the crazed regions via matrix shearing. The extensive damage zone is believed to result in a reduction in stress intensity at the crack tip thereby reducing the crack propagation rates. For the reprocessed nylon 66, one observes fewer crazes and a sharper fatigue crack tip with a consequent acceleration in crack propagation rates and a smoother fracture surface.