Experimental and 3D numerical analysis on the effect of specimen thickness on fracture toughness of Al6061-SiC-cenosphere Hybrid composites

The fracture behaviour of a polyetherimide (PEI) thermoplastic polymer was studied using compact tension (CT) specimens with a special emphasis on effects of specimen thickness and testing temperatures on the plane strain fracture toughness. The results show that the valid fracture toughness of the critical stress intensity factor, K IC, and strain energy release rate, G IC, is independent of the specimen thickness when it is larger than 5 mm at ambient temperature. On the other hand, the fracture toughness is relatively sensitive to testing temperatures. The K IC value remains almost constant, 3.5 MPa $$\sqrt {\text{m}} $$ in a temperature range from 25 to 130°C, but the G IC value slightly increases due to the decrease in Young's modulus and yield stress with increasing temperature. The temperature dependence of the fracture toughness, G IC, was explained in terms of a plastic deformation zone around the crack tip and fracture surface morphology. It was identified that the larger plastic zone and extensive plastic deformation in the crack initiation region were associated with the enhanced G IC at elevated temperatures.

Effects of hydrogen and specimen thickness on fracture toughness of ferritic steel welded joint

The effects of specimen thickness on fatigue crack growth rate (FCGR) and acoustic emission (AE) behaviors of Q345 steel were investigated. The four-point bending fatigue tests were carried out with AE monitoring simultaneously. Based on the thickness effect analysis, fatigue behavior studies, and AE investigations, the effects of specimen thickness on AE signal and AE source mechanisms during fatigue crack propagation were proposed. The results show that as specimen thickness increased, the FCGR was accelerated slightly, while the AE count rate was increased significantly, suggesting that AE signal was more sensitive to the changes in thickness. By analyzing the AE signals at the new plastic yielding area and the crack tip micro-fracture process, AE source mechanisms were explained. These results suggest that the effects of thickness must be considered to obtain a more accurate estimation of fatigue crack propagation through AE technique.

The main purpose of the present paper is to investigate the effect of strain rate, specimen thickness and welding on the fracture toughness. The material of the investigated pipe is a high-density polyethylene, (HDPE) which is commonly used in natural gas piping systems. The welding technique used in this study is butt fusion (BF) welding technique. The crosshead speed ranged from 5 to 500 mm/min and specimen thickness ranged from 9 to 45mm for both welded and unwelded specimens at room temperature, Ta equal 20 °C. Curved three point bend (CTPB) specimens were used to determine KQ. Furthermore, the results of fracture toughness, KQ, will be compared with the plane strain fracture toughness, JIC, for welded and unwelded specimens. The experimental results revealed that KQ increases with increasing the crosshead speed, while KQ decreases as the specimen thickness increases. The investigation reveals that the apparent fracture toughness, KQ, for HDPE pipe of unwelded specimen is greater than that of corresponding value for welded specimen. The same trend was observed for the plane strain fracture toughness, JIc. At lower crosshead speeds there is a minimum deviation in KQ between welded and unwelded specimens, while the deviation becomes larger with increasing crosshead speed.

Effects of microstructure and specimen thickness on the fatigue crack closure in Al-Li 8090 alloy

Size requirements for a pin-loaded double-edge notch plus crack tension specimen proposed for fracture toughness screening heavy-section alloys were studied. Ranking of eight selected alloys based on the specimen's net strength was compared with that based on the valid plane-strain fracture toughness separately determined. Performance of the specimen was judged on the basis of that comparison. The specimen's net strength was influenced by three critical specimen dimensions: distance between the crack plane and the loading hole, specimen width, and specimen thickness. Interaction between the stress fields of the crack and the loading holes reduced the net strength, but this effect disappeared as the separation reached a dimension equal to the specimen width. The effects of specimen width and thickness are interrelated and affect the net strength through their influence on the development of the crack-tip plastic zone. Correlation between the net strength of the screening specimen and the plane-strain fracture toughness was enhanced by increasing thickness and decreasing width of the screening specimen. The work described is intended to form the technical base for the development of a standard fracture toughness screening test method for heavy sections to supplement ASTM E 338 Standard Method of Sharp Notch Tension Testing of High-Strength Sheet Materials. Development of the test method is the responsibility of the ASTM E24.01.02 Task Group on Revision of E 338.

Effect of specimen thickness on the fracture resistance of hot mix asphalt in the disk-shaped compact tension (DCT) configuration

In order to evaluate the fracture toughness (J IC ) of JN1 austenitic stainless steel rolled plate, we performed elastic-plastic fracture toughness tests with standard and modified compact tension specimens at liquid helium temperature. These tests were conducted in accordance with ASTM standards E813–81 and E813–87 for determining J IC using the unloading compliance method to monitor crack growth. The effects of specimen thickness and side-groove on J IC and tearing modulus (T mat ) are reported. The final value of physical crack extension was taken as the average of nine measurements using an optical microscope. Fracture surfaces were examined by scanning electron microscopy (SEM) to verify the failure mechanisms. The effects of crack tunneling on the determination of J-integral resistance curves and valid J IC values, and a difference between ASTM standards E813–81 and E813–87 are also discussed.

In order to study the fracture behaviour of hydroxyl‐terminated polybutadiene (HTPB) propellant, the low temperature fracture toughness experiment of HTPB propellant was carried out by using centrally cracked sheet tensile specimens. The fracture toughness values of HTPB propellant with mode I crack at different temperature and loading rate were obtained, and the effect of specimen thickness on the fracture toughness was investigated. The experimental results show that the fracture toughness value continuously increases with the decreasing of temperature and the increasing of loading rate, and a linear relationship exists between the fracture toughness and the logarithm of loading rate. The effect on the fracture toughness by the change in loading rate is more notable at a lower temperature. Both at 25 °C and −40 °C, the fracture toughness of thick specimens is higher than that of thin specimens, and at low temperature the change is more obvious. A master curve of quadratic function for the fracture toughness was obtained. The influence of temperature on the fracture toughness is more obvious than that of the strain rate with double factor analysis of variance.

The effect of constraint on CTOD fracture toughness of API X65 steel

The measuring method of CTOD, the effects of notch position, heat treatment, specimen thickness and test temperature on CTOD and the CTOD design curves are examined using a 200 mm thick, mild steel plate and its welded joint. The CTOD measuring method of BS5762 is confirmed. The effect of specimen thickness on CTOD is established. The CTOD design curve which significantly depends on the gage length for measuring strain must be established by taking into account actual conditions such as variance of strength as in welded joint. INTRODUCTION The development of tough steels and sound design practice have led to the safety of offshore structures. The use of thicker plates and the increasingly severe operating and environmental conditions, however, require more intensive effort for safety assurance. The use of fracture mechanics is one of such efforts. Though the linear elastic fracture mechanics is clearly established and its application is easy, it cannot be applied in general to offshore structures because the materials used are tough. The non-linear elastic-plastic fracture mechanics, therefore, is widely used for designing and safety evaluation of offshore structures. The most typical fracture parameter is crack tip opening displacement (CTOD). The CTOD concept, however, is based on the experimental results obtained with materials as thick as up to 50 mm in general. Since heavier section steel plates and their welded joints are used in construction of offshore structures, the CTOD concept must be reexamined from the view points of measurement and application. The present paper examines the measuring method of CTOD, the effect of notch position, heat treatment, specimen thickness and test temperature on CTOD and the CTOD design curve using a 200 mm thick, mild steel plate and its narrow gapped submerged arc welded joint. EXPERIMENTAL PROCEDURE MATERIALS TESTED The materials tested were a 200 mm thick steel plate (BS4360-43E) and its narrow gapped submerged arc welded joint. The chemical composition and mechanical properties of the steel are listed in Table 1. The welding conditions are listed in Table 2.Table 3 shows the chemical composition and mechanical properties of weld metal. FRACTURE TOUGHNESS TEST Figure 1 shows the dimensions of three point bend specimens and test conditions. The specimens with reduced thickness were cut from the mid thickness portion of the original plate and its welded joint. The test and measurement of CTOD were carried out according to BS5762[1]. Figure 2 illustrates the procedure for determining rotational factor for three point bend test. The rotational factor was determined geometrically using five clip gages mounted on each specimen. The wide plate tensile test was performed with four specimens whose geometries are shown in Fig. 3. One specimen was of base metal with surface notch. Three specimens were notched in fusion line; one with surface notch and two with through thickness notches.

Time-dependent fracture of epoxy resin under mixed-mode I/III loading

This paper describes examinations of the requirements for fracture toughness of piping materials to establish Leak-Before-Break (LBB) behaviors. One of the important elements in establishing LBB is the fracture toughness of the materials. The fracture toughness might vary greatly due to inappropriate material management. Some representative fracture toughness properties of piping materials are plane strain fracture toughness (KIc or JIc) and fracture resistance curve (J-R curves). Requirements to establish LBB were examined focusing on these two properties. Although it is easy to obtain plane strain fracture toughness (it can, for example, be estimated using the Charpy impact test, etc.), trying to predict ductile fracture strength based only on plane strain fracture toughness will likely result in underestimating the strength. In the LBB Codes of the Japan Society of Mechanical Engineers (JSME), the elastic-plastic fracture mechanics (EPFM) have been defined for the material that shows ductile fracture behaviors. The LBB Codes set the ratio of the plastic collapse strength and ductile fracture strength (Pb′/Pb-cr) as 1.5 or less. Therefore, requirements for the fracture resistance of the piping materials to have the same fracture strength as the LBB Codes were examined. The examinations have shown that the slope of the fracture resistance curve is as important as the plane strain fracture toughness (JIc). In order to achieve the same ductile fracture strength with EPFM defined in the LBB Codes, the fracture resistance of the pipe materials should be controlled plane strain fracture toughness (JIc) and fracture resistance curve. Materials with high fracture toughness should be used, especially when employing thin-walled or high yield stress pipes.

Electron beam welding was used to make joints of SUS 405 steel. Compact tension type specimens with incomplete penetration notches were extracted from the electron beam welds. Fracture toughness tests were carried out at room temperature for the specimens in the as-welded and postweld heat-treated (685°C×2, 4 and 8 hours) conditions.In all cases, cracks propagated in the middle of electron beam weld. Because of the natural complicated crack shape etc., a large scatter appeared in the fracture toughness, Jc. The PWHT tended to improve the fracture toughness. The effect of specimen thickness on fracture toughness Jc was also examined. The statistical model based on a Weibull distribution indicated that the fracture toughness obtained by small specimens can be used to characterize that of large specimens or real structures.

The fracture toughness (KIC) of high strength casing steel (1130 MPa) has been determined by a three-point-bend specimen. Three specimens with thicknesses of 5 mm, 8 mm and 10 mm, respectively have been used to observe the effect of thickness on the fracture toughness of steel. The analytical formula of the relationship between the fracture toughness and material thickness of high strength casing (1130 MPa) is proposed based on the energy theory and on linear elastic mechanics. The values of fracture toughness, K, measured by three thicknesses of parent metals are combined with the quantitative model of the relationship between fracture toughness and specimen thickness. The material constant (and κ) are calculated by using the least squares method. Furthermore, an analytic formula for the relationship between fracture toughness and specimen thickness is proposed which allows for the calculation of the KIC value. Plane-strain fracture toughness (KIC = 133.94 MPa × m1/2) is a fixed value only if the thickness of the specimen exceeds 43 mm. Fracture toughness values of different thicknesses of high strength casing are derived by fracture toughness tests of several thicknesses based on the model in question in order to save manpower and material resources. This method is also significant for measuring the fracture toughness of other OCTG, since their thicknesses do not meet the requirement of the standard test methods. For the present, it provides general methods and reference rules for obtaining the KIC of other metallic OCTG.