Browsing by Author "LU, ML"

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A NEW APPROACH IN J-INTEGRAL METHOD BASED ON HYSTERESIS ON DUCTILE POLYMERIC MATERIALS
(1992-04-05)
LEE, CB
;
LU, ML
;
CHANG, FC
;
應用化學系
;
Department of Applied Chemistry
DETERMINATION OF J(C) FOR A POLYCARBONATE (PC) POLY(BUTYLENE TEREPHTHALATE) (PBT) BLEND-BASED ON THE ANALYSES OF MULTIPLE-SPECIMEN J-R CURVES
(1995-11-01)
LU, ML
;
CHANG, FC
;
應用化學系
;
Department of Applied Chemistry
Various regression models and data windows have been used to examine the multiple-specimen J integral analysis to provide the best estimate of fracture toughness. The linear regression model (similar to ASTM E813-81) results in the least accuracy in the data fitting and is highly sensitive to the data window. The power law model (similar to ASTM E813-87) gives a better data fitting and is less sensitive to the data window. The polynomial regression models with higher orders (n = 3 and 4) give the best data fitting. True crack initiation occurs gradually rather than as an abrupt event, and therefore the critical J strictly based on initiation could be in error. ASTM E813-81 based on the theoretically predicted blunting line tends to give an underestimated J(c). The power law approach of ASTM E813-87 indeed provides a better data fitting but suffers the disadvantage of an overestimated J(c) owing to the 0.2 mm offset line. The 0.1 mm offset line approach proposed here results in the most consistent J(c) regardless of the regression models and data windows selected.
Fracture toughness of PC/ABS blend under different stain rates by various J-integral methods
(1995)
LU, ML
;
CHANG, FC
;
應用化學系
;
Department of Applied Chemistry
FRACTURE-TOUGHNESS OF A POLYCARBONATE/ACRYLONITRILE-BUTADIENE-STYRENE BLEND BY THE ASTM E813 AND HYSTERESIS ENERGY J-INTEGRAL METHODS - EFFECT OF SPECIMEN THICKNESS AND SIDE GROOVE
(1995-06-01)
LU, ML
;
CHANG, FC
;
應用化學系
;
Department of Applied Chemistry
A previously developed non-conventional J integral based on hysteresis energy and the ASTM E813 methods have been employed to test the fracture toughness of a polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) blend. A systematic study of the effect of the specimen thickness (from B=4 to 15 mm) and the presence of a V-shaped side groove on the resultant J(1c) has been carried out. The results show that the J(1c) values obtained from the hysteresis energy method and the E813-81 method are comparable, but are similar to 60-90% lower than those obtained from the E813-87 method. When the specimen thickness is relatively thin, the J(1c) values obtained from the V-shaped-side-grooved specimens are slightly higher than those from samples without the side groove, but this difference gradually decreases with an increase in the specimen thickness. The J(1c) values obtained from the ungrooved specimens are almost independent of the specimen thickness (from B=4 to 15 mm) for all of these methods. The critical initiation displacements in terms of the onset of crack initiation, determined from the plots of hysteresis energy vel sus displacement, hysteresis ratio versus displacement, and crack growth length versus displacement, are fairly close in value. This means that the critical crack initiation and the corresponding J(1c) obtained from this hysteresis energy method indeed represent the actual physical event of the onset of crack initiation.
FRACTURE-TOUGHNESS OF ACRYLONITRILE-BUTADIENE-STYRENE BY J-INTEGRAL METHODS
(1995-09-01)
LU, ML
;
LEE, CB
;
CHANG, FC
;
應用化學系
;
Department of Applied Chemistry
The fracture toughness of acrylonitrile-butadiene-styrene (ABS) was determined by three J-integral methods, ASTM E813-81, E813-87, and by hysteresis. The critical J values (J(1c)) obtained are fairly independent of the specimen thickness, ranging from 10 to 15 mm. ASTM E813-81 and hysteresis methods result in comparable J(1c) values, whereas the ASTM E813-87 was similar to 40% to 50% higher. The critical displacement determined from the plots of hysteresis (energy or ratio) and the true crack grow length vs. displacement are close. This indicates the critical displacement determined by the hysteresis method is indeed the displacement at onset of crack initiation, and the corresponding J(1c) represents a physical event of crack initiation. The elastic storage energy, the input energy minus the hysteresis energy, is the most important factor in determining the onset of crack initiation. The critical elastic storage energy (at the beginning of crack growth) was found close to the J(1c) obtained from the E813-81 or the hysteresis method.
FRACTURE-TOUGHNESS OF HIGH-IMPACT POLYSTYRENE BASED ON 3 J-INTEGRAL METHODS
(1993-03-10)
LEE, CB
;
LU, ML
;
CHANG, FC
;
應用化學系
;
Department of Applied Chemistry
Three J-integral methods and their modified versions have been used to characterize the fracture toughness of high-impact polystyrene (HIPS) with different thicknesses. The Jc values obtained were highest from the E813-87 method, followed by the E813-81 method, then by the hysteresis method. The hysteresis method based on the steep rising of hysteresis energy under constant displacement-controlled loading in Jc determination has many advantages over the ASTM E813-81 or the E813-87 method. The requirement of crack growth length measurements is no longer necessary and the controversial issue on the crack blunting line can also be avoided. The E813-87 method-resulted in significantly higher Jc values for polymers' but the modified version of E813-87, by moving the offset line from the original 0.2 to 0.1 mm, resulted in comparable Jc values. Since crazes as the main failure mechanism for HIPS, well-defined crack blunting does not expect to occur and the Jc obtained by the original E813-81 based on the theoretically predicted blunting line is indeed slightly higher. The modified version of E813-81 by neglecting the blunting line in Jc determination is believed to be more reasonable for HIPS. The nature of polymers will determine whether the crack tip will be blunted, partially blunted, or not blunted. ASTM E813-81 is appropriate for those polymers with a well-defined blunted crack tip (such as elastomer-modified poly-carbonate), whereas the modified version of ASTM E813-81 seems better for those polymers with craze as the main failure mechanism (such as HIPS). Experimental results indicated that this hysteresis method is able to inherently adjust the crack blunting effect and therefore can be applied to any type of ductile polymer.
FRACTURE-TOUGHNESS OF PC/PBT BLEND-BASED ON J-INTEGRAL METHODS
(1995-05-31)
LU, ML
;
CHANG, FC
;
應用化學系
;
Department of Applied Chemistry
The fracture toughness of a polycarbonate/poly(butylene terephthalate) (PC/PBT) blend was determined using three different J-integral methods, ASTM E813-81, E813-87, and hysteresis energy. The critical J values (J(1c)) obtained are largely independent of the cross-head speed (range from 0.5 to 50 mm/min). ASTM E813-81 and hysteresis energy methods result in comparable J(1c) values, while the E813-87 method estimates J(1c) to be 60-80% higher. The critical displacement determined from the plots of hysteresis (energy and ratio) and the true crack growth length vs. displacement is very close. This indicates that the critical displacement determined by the hysteresis energy method is indeed the displacement at the onset of crack initiation and the corresponding J(1c) represents a physical event of crack initiation. (C) 1995 John Wiley and Sons, Inc.