• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.653-660
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• 1986

Two uppor bound solutions, by the force balance method and by a kinematically admissible velocity field, are compared for the metal forming problems in plane strain. It is concluded that these two approaches always give identical results when the geometrical configurations of the deformation model reman the same. By detailed derivations for plastic bending of a notched bar, closed die forging, compression of a rectangular block, machining with a restricted contact tool and plane strain backward extrusion, the identity of both approaches is verified.

• International Journal of Highway Engineering
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• v.17 no.3
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• pp.77-83
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• 2015

PURPOSES : In this study, a fracture-based finite element (FE) model is proposed to evaluate the fracture behavior of fiber-reinforced asphalt (FRA) concrete under various interface conditions. METHODS : A fracture-based FE model was developed to simulate a double-edge notched tension (DENT) test. A cohesive zone model (CZM) and linear viscoelastic model were implemented to model the fracture behavior and viscous behavior of the FRA concrete, respectively. Three models were developed to characterize the behavior of interfacial bonding between the fiber reinforcement and surrounding materials. In the first model, the fracture property of the asphalt concrete was modified to study the effect of fiber reinforcement. In the second model, spring elements were used to simulated the fiber reinforcement. In the third method, bar and spring elements, based on a nonlinear bond-slip model, were used to simulate the fiber reinforcement and interfacial bonding conditions. The performance of the FRA in resisting crack development under various interfacial conditions was evaluated. RESULTS : The elastic modulus of the fibers was not sensitive to the behavior of the FRA in the DENT test before crack initiation. After crack development, the fracture resistance of the FRA was found to have enhanced considerably as the elastic modulus of the fibers increased from 450 MPa to 900 MPa. When the adhesion between the fibers and asphalt concrete was sufficiently high, the fiber reinforcement was effective. It means that the interfacial bonding conditions affect the fracture resistance of the FRA significantly. CONCLUSIONS : The bar/spring element models were more effective in representing the local behavior of the fibers and interfacial bonding than the fracture energy approach. The reinforcement effect is more significant after crack initiation, as the fibers can be pulled out sufficiently. Both the elastic modulus of the fiber reinforcement and the interfacial bonding were significant in controlling crack development in the FRA.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.12
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• pp.1393-1400
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• 2009

The objective of this study is to validate local failure criteria, which were proposed based on the notched-bar specimen tests combining with finite element (FE) simulations, using the results of real-scale pipe failure tests. This study conducted burst test using wall-thinned pipe specimens, which were made of 4 inch Sch.80 ASTM A106 Gr.B carbon steel pipe, under simple internal pressure at ambient temperature and performed associated FE simulations. Failure pressures were estimated by applying the failure criteria to the results of FE simulations and were compared with experimental failure pressures. It showed that the local stress based criterion, given as true ultimate tensile stress of material, accurately estimated the failure pressure of wall-thinned pipe specimens. However, the local strain based criterion, which is fracture strain of material as a function of stress tri-axiality, could not predict the failure pressure. It was confirmed that the local stress based criterion is reliably applicable to estimation of failure pressure of local wall-thinned piping components.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.787-797
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• 1986

An implicit approach is employed to obtain a general boundary integral formulation of axisymmetric elastic problems in terms of a pair of singular integral equations. The corresponding kernel functions from the solutions of Navier's equation are derived by applying a three dimensional integral and a direct axisymmetrical approach. A numerical discretization schem including the evaluation of Cauchy principal values of the singular integral is described. Finally the typical axisymmetric elastic models are analyzed, i.e. the hollow sphere, the constant thickness and the V-notched round bar.

• Journal of Welding and Joining
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• v.23 no.6
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• pp.87-92
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• 2005

It has been well hewn that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using a two-parameters criterion based on equivalent plastic strain and stress triaxiality. The present study focuses on the effects of strength mismatch, which can elevate plastic constraint due to heterogeneous plastic straining, on the critical condition for ductile fracture initiation usinga two-parameter criterion. Fracture initiation testing has been conducted under static loading using notched round bar specimens which had different notch locations. This study provides the fundamental clarification of the effect of strength mismatching and effect of notch location on the critical condition to ductile crack initiation from notch root using fuite element method and ultrasonic-mechatronics system. The critical condition of ductile crack initiation from notch root of strength mismatched tensile specimens under static loading appeared to be almost the same as those of homogeneous tensile specimens with circumferential sharp notch specimen. Also, the effect of notch location in mismatched specimens was estimated using finite element(FE) analyses.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2386-2394
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• 2022

In this paper, smooth and notched bar tensile tests of austenitic stainless steel 304 are performed, covering four different multi-axial stress states and six different strain rate conditions, to investigate the effect of the stress triaxiality and strain rate on fracture strain. Test data show that the measured true fracture strain tends to decrease with increasing stress triaxiality and strain rate. The test data are then quantified using the Johnson-Cook (J-C) fracture strain model incorporating combined effects of the stress triaxiality and strain rate. The determined J-C model can predict true fracture strain overall conservatively with the difference less than 20%. The conservatism in the strain-based acceptance criteria in ASME B&PV Code, Section III, Appendix FF is also discussed.

• The Journal of Advanced Prosthodontics
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• v.5 no.1
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• pp.36-43
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• 2013

PURPOSE. The objective of this study was to compare the fracture toughness ($K_{Ic}$) obtained from the single edge V-notched beam (SEVNB) and the fractographic analysis (FTA) of a glass-infiltrated and a zirconia ceramic. MATERIALS AND METHODS. For each material, ten bar-shaped specimens were prepared for the SEVNB method ($3mm{\times}4mm{\times}25mm$) and the FTA method ($2mm{\times}4mm{\times}25mm$). The starter V-notch was prepared as the fracture initiating flaw for the SEVNB method. A Vickers indentation load of 49 N was used to create a controlled surface flaw on each FTA specimen. All specimens were loaded to fracture using a universal testing machine at a crosshead speed of 0.5-1 mm/min. The independent-samples t-test was used for the statistical analysis of the $K_{Ic}$ values at ${\alpha}$=0.05. RESULTS. The mean $K_{Ic}$ of zirconia ceramic obtained from SEVNB method ($5.4{\pm}1.6\;MPa{\cdot}m^{1/2}$) was comparable to that obtained from FTA method ($6.3{\pm}1.6\;MPa{\cdot}m^{1/2}$). The mean $K_{Ic}$ of glass-infiltrated ceramic obtained from SEVNB method ($4.1{\pm}0.6\;MPa{\cdot}m^{1/2}$) was significantly lower than that obtained from FTA method ($5.1{\pm}0.7\;MPa{\cdot}m^{1/2}$). CONCLUSION. The mean $K_{Ic}$ of the glass-infiltrated and zirconia ceramics obtained from the SEVNB method were lower than those obtained from FTA method even they were not significantly different for the zirconia material. The differences in the $K_{Ic}$ values could be a result of the differences in the characteristics of fracture initiating flaws of these two methods.

• Elastomers and Composites
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• v.41 no.3
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• pp.172-181
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• 2006

Flame retardant synergism of phyllite was studied in ABS resins containing brominated flame retardant(tetrabromobisphenol A(TBBA) or brominated epoxy oligomer(BEO)) and antimony trioxide($Sb_2O_3)$. Talc was used for the comparison purpose. ABS compounds were manufactured by a twin-screw co-rotating extruder and subsequently injection molded into several specimen for mechanical and thermal properties. Flame retardancy of ABS compounds measured by UL 94 vertical test with 1.6 mm thick bar specimen was enhanced by the replacement of antimony trioxide into phyllite or talc in the range of 12.5%(0.5 wt%) to 37.5%(1.5 wt%). Phyllite showed better synergistic effect comparing with talc especially for BEO. Only phyllite enhanced the flowability of ABS compounds. Notched Izod impact strength decreased with the proportion of phyllite or talc content. Phyllite could replace the antimony trioxide up to the content of 25%(1 wt%) to give better flame retardancy and flowability without darkening problem.

• The Journal of Advanced Prosthodontics
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• v.14 no.5
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• pp.285-293
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• 2022

PURPOSE. This study evaluated the relationship among translucency, crystalline phase, grain size, and fracture toughness of zirconia. MATERIALS AND METHODS. Four commercial zirconia - Prettau^®Anterior^® (PA), Prettau^® (P), InCorisZI (ZI), and InCorisTZI (TZI)- were selected for this study. The bar specimens were prepared to determine fracture toughness by using chevron notched beam method with four-point bending test. The grain size was evaluated by a mean linear intercept method using a scanning electron microscope. X-ray diffraction and Rietveld refinement were performed to evaluate the amount of tetragonal and cubic phases of zirconia. Contrast ratio (CR) was measured to investigate the level of translucency. RESULTS. PA had the lowest fracture toughness among other groups (P < .05). In addition, the mean fracture toughness of P was significantly less than that of ZI, but there was no difference compared with TZI. Regarding grain size measurement, PA had the largest average grain size among the groups. P obtained larger grain size than ZI and TZI (P < .05). However, there was no significant difference between ZI and TZI. Moreover, PA had the lowest CR value compared with the other groups (P < .05). This means PA was the most translucent material in this study. Rietveld refinement found that PA presented the greatest percentage of cubic phase, followed by TZI, ZI, and P, respectively. CONCLUSION. The different approaches are used by manufacturers to fabricate various types of translucent zirconia with different levels of translucency and mechanical properties, which should be concerned for material selection for successful clinical outcome.