ASTM E813-81 Research Articles

Fracture toughness characterizations of compatibilized polyamide-6 (PA6)/poly(phenylene ether) (PPE) blends

Under the plane-strain condition, the material properties, KIC and GIC, of the blends, brittle or with small-scale yielding, increase with increasing elastomer content. To evaluate the critical J-integral for the ductile blends, several methods have been compared to understand the influence of elastomer content and different thicknesses using single-edge notch-bend specimens. For a given thickness, the fracture toughness increases with increasing elastomer content. Moveover, the slope of the R-curve becomes gradually steeper with increasing elastomer content and decreasing specimen thickness. JIC values determined from ASTM E813-89 and modified ASTM E813-81 methods always give the highest and the lowest values, respectively. JIC values determined from three other methods are comparable and can be employed to characterize the fracture toughness of the compatibilized PA6/PPE blends. It is noted that JIC values determined from the modified ASTM E813-89 and the hysteresis energy methods are apparently independent of thickness. Therefore, these two methods may be considered as potential alternative techniques to evaluate the critical J-integral for toughened polymer blends.

Effect of temperature on fracture toughness of PC/ABS based onJ-integral and hysteresis energy methods

SYNOPSIS The critical fracture toughness J,, of the polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) blend at different temperatures was obtained from ASTM E813-81, E813-87, and the recently developed hysteresis energy methods, respectively. The J1, value increases with increase of the test temperature ranging from -60 to 70°C. The hysteresis energy method and the ASTM E813-81 method result in comparable J1, values, while the ASTM E813-87 results in about 80-1 10% higher values. The critical initiation displacements determined from the plots of hysteresis energy and the true crack growth length vs. crosshead displacement are very close. This indicates that the critical initiation displacement determined by the hysteresis method is indeed the displacement at the onset of true crack initiation and the corresponding J,, represents a physical event of crack initiation. The fracture toughness, K1, value, based on linear elastic fracture mechanics (LEFM), was determined by using KQ analysis (ASTM E399-781, and the obtained KQ value decreases with the increase of the test temperature. The K, value is not the real LEFM K1, value because the criterion of P,,,/PQ < 1.1 has not been satisfied. However, the corresponding JQ obtained from the KO analysis is comparable to the J,, obtained from the E813-81 method at lower temperature (-45 or -6OoC), an indication of LEFM behavior at lower temperature. The various schemes and size criterion based on LEFM and the J-method are explored for the validity of J1, and K1, values. 0 1996 John Wiley & Sons, Inc.

Elastic-plastic fracture toughness of PC/ABS blend based on CTOD and J-integral methods

The elastic-plastic fracture toughness of a PC/ABS blend has been investigated simultaneously by the conventional J-integral and the crack tip opening displacement (CTOD) methods for specimen thickness varying from 4 to 15 mm. The critical J (Jc) and the critical CTOD (δc) are based on crack initiation. Another new method to determine Jc based on the close relationship between the J-integral and CTOD has also been developed. Those three critical Jc values, Jc−81, Jc-NEW, and Jc-BS obtained from ASTM E813-81, the new J method, and the equation Jc = mσyδc (1−ν2) of the CTOD method, are comparable and are independent of the specimen thickness. The constraint factor m evaluated from the linear elastic fracture mechanics (LEFM) approach using the Dugdale model is about 1.5. A rotation factor rg of approximately 2 was obtained which is also independent of the specimen thickness. The crack propagation resistance, J-curve (dJ/da) or δ-curve (dδ/da), decreases with increasing specimen thickness. A close relationship between CTOD and J-integral has been demonstrated in this study.

Fracture toughness of PC/PBT blend based on J‐integral methods

AbstractThe 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 (J1c) 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 J1c values, while the E813‐87 method estimates J1c 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 J1c represents a physical event of crack initiation. © 1995 John Wiley &amp; Sons, Inc.

Determination of Jc for a polycarbonate (PC)/poly(butylene terephthalate) (PBT) blend based on the analyses of multiple-specimen J— R curves

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.

Optimum regression model and data-window on J-integral method based on hysteresis on PC/PBT blend

The J-Integral fracture mechanics based on an hysteresis approach has been previously demonstrated to be viable and simple experimentally. However, the optimum procedure to construct the J-R curve in terms of regression model and data-window has not yet been well defined. In this study, the fracture toughness of the PC/PBT blend has been investigated using the previously developed hysteresis method by seven regression models and three data-window ranges. The second order polynomial model results in the best data-fitting capability and moreconsistent Jc values than those higher order polynomial models or the linear regression model. The critical J values obtained from this second polynomial model using the same data-window as ASTM E813-81 standard are comparable to those obtained from the ASTM standards. The trend clearly shows thathigher Jc values are obtained when the range of data-window is increased. The close Jc values obtained from this hysteresis method and the ASTM E813-81 indicate that the determined critical displacement from this hysteresis method is indeed the onset of crack initiation.

Single and multi-specimenR-curve methods forJ IC determination of toughened nylons

For characterization of the fracture resistance of materials used in the upper shelf toughness regime,J-R curves are widely considered the most promising candidates. However, there still remain problems concerning both the generation and measurement ofJ-R curves as material characterizing parameters and their application in ductile fracture analyses for failure prediction in polymeric materials. This paper reports the results of investigations conducted on two rubbertoughened nylons at room temperature. Two different methods ofJ-R curve determination are covered, namely multi-specimen and single specimen test methods. The resultingJ-R curves have also been evaluated to obtain values of the initiation toughness,JIC, following the extrapolation and interpolation schemes prescribed by ASTM E813-81 and ASTM E813-87 test procedures, respectively. The results show that the multiple specimen unloading method and the single specimen partial unloading compliance method can be used to generate comparable crack growth resistanceJ-R curves of the toughened nylons. The value ofJIC for the crystalline rubber-toughened nylon was approximately twice the value obtained for the amorphous rubber-toughened nylon. The former material also exhibited a greater resistance to ductile crack growth.

A general formula for three-point bend specimen J-integral calculation

This article gives a general formula for three-point bend specimen J-integral calculation. This formula can be used when a 0 W ⩾ 0.5 , as the well known formula J = A Bb · f( a 0 W ) given in standard ASTM E813-81, and can also be used when a 0 W < 0.5 . Therefore it is very useful for practical use.

A comparison of several analytical techniques for calculating [formula omitted] Curves from load-displacement data and their relation to specimen geometry

Various methods to determine crack growth resistance curves have been compared. Ferritic ductile cast iron (grade 60-40-18) was machined into three different specimen geometries (compact tension, bend bar and Charpy V-notched) which were fatigue precracked and then tested under displacement control at room temperature. Crack resistance curves were generated using the current standard, ASTM E813-81, and a new J-R curve standard, ASTM E1152-87. It was found that R- curves calculated with these two approaches were similar up to approximately 1 to 3 mm of crack extension, at which point the R- curve calculated with ASTM E1152-87 began to drop off. A geometry dependence of the R- curves was observed between the different specimen geometries for both ASTM E813-81 and ASTM E1152-87. The modified J formulation of Ernst was also found to give a geometry dependent R- curve for the ferritic ductile iron.

オーステナイトステンレス鋼（ＳＵＳ３１６ＬＮ）の極低温破壊靭性に及ぼす試験片寸法効果

This investigation has been carried out to determine the influence of specimen size and side groove depth on elastic-plastic fracture toughness parameters. Elastic-plastic fracture toughness JIC and tearing modulus Tmat were evaluated by the unloading compliance method which was described in ASTM E813-81 standards. Compact tension specimens were prepared from SUS316LN and the test were conducted at cryogenic temperature 4.2K. It is understood that JIC and Tmat are independent of specimen size when the specimen satisfies ASTM standard size requirements. JIC and Tmat decrease with the increase of side groove depth for 0-12.5% of original thickness, and they are independent of side groove depth when the depth is 12.5-37.5%. These results suggest that a 0.5CT small specimen with 25% side grooves can provide proper JIC and Tmat values independent of specimen size and side groove depth.

Effect of size on elastic-plastic fracture toughness for SUS316LN at cryogenic temperature.

This investigation has been carried out to determine the influence of specimen size and side groove on elastic-plastic fracture toughness parameters. Elastic-plastic fracture toughness JIC and tearing modulus Tmat were evaluated by the unloading compliance method which describes ASTM E813-81 standards. A compact tension specimen was prepared from SUS316LN and the test was conducted at cryogenic temperature 4.2K. It is understood that JIC and Tmat were independent of specimen size when the specimen satisfied ASTM standard size requirements. JIC and Tmat decrease with the increase of side groove for 0-12.5%, and they are independent of the side groove when the side groove is 12.5-37.5%. These results suggest that a 0.5 CT small specimen with a 25% side groove can provide a proper JIC and Tmat independent of specimen size and side groove.

Proposed modifications of ASTM E813-81 standard test method for JIc

This paper contains a critical examination of the present ASTM E813-81 JIc test standard and proposed modifications of this standard. It is suggested that a value J corresponding to a ductile tearing, Δa∗, of 0.2 mm be regarded as an engineering approximation of initiation fracture toughness. This amount of ductile tearing is obtained by intersecting the initial part of the J-Δa curve with an intercept line parallel to the blunting line. An improved blunting line has been derived by accounting for the material's strain hardening properties. Finally, the application of the modified JIc procedure will be demonstrated using several materials.