• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.6
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• pp.504-511
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• 2008

This study evaluated the influence of the strength mismatch of HAZ for a plastic ${\eta}$-factor, which is the principle parameter determining the plastic portion of J-integral to assess the fracture toughness of the weldment. The specimen of tensile and hardness test was manufactured from the piping applying narrow-gap welding, and the mechanical properties of weldment, HAZ and a base metal were obtained. To perform the finite element analysis according to the ratio of strength mismatch, the material properties was chosen with the change of strength using the determination method of Ramberg-Osgood constant. Also, the influence of the strength mismatch of HAZ was determined using finite element analysis by those properties.

• Journal of Welding and Joining
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• v.18 no.6
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• pp.83-88
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• 2000

Variation of welded-joint hardness and tensile strength of a accelerated-cooled fine-grained ferritic-pearlitic steel with heat input was investigated. In a weld heat-affected zone, a softened zone was formed and it had lower hardness than that of a base metal. While the width of a softened zone increased continuously with an increase of heat input up to 100kJ/cm. the minimum hardness in a softned zone was almost constant after a continuos decrease up to 60KJ/cm. Because of a softened zone, the welded-joint was fractured in the HAZ and its maximum reduction of tensile strength was about 20%. Measured welded-joint tensile strength and calculated minimum tensile strength in a welded-joint was almost same, which means that the plastic restraint of a softened zone did not occur in this experiment. It is believed that as a softened zone width-to-specimen thickness ratio is as high as 2~6 in this experiment, the plastic restraint effect does not occur. Theoretical analysis shows that the plastic restraint effect occurs only when the ratio is below 0.5.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.3
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• pp.225-232
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• 2014

This paper concerns the mechanical properties of recycled plastic fiber-reinforced concrete. It presents experimental research results of recycled fiber-reinforced concrete with fiber volume fractions of 0, 0.5, 1.0, 1.5, and 2%. Experiments were performed to measure mechanical properties such as compressive strength, elastic modulus, tensile strength, and length changes. The results show that both compressive strength and elastic modulus decreased as fiber volume fraction increased. In addition, the experimental results show that recycled fiber-reinforced concrete is in favor of split tensile strength, flexural tensile strength, characteristic regarding crack mouth opening displacement, and length changes. The results of this study can be used to provide realistic information for modeling of mechanical properties in recycled plastic fiber-reinforced concrete in the future.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.3
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• pp.375-380
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• 2020

In this study, we tried to evaluate the mechanical properties of Polycarbonate(PC) and acrylonitrile-butadiene-styrene(ABS) plastic materials, which are frequently used as parts of home appliances and machinery, when repeated impacts were applied. A repeating impact tester for this research was designed and manufactured to apply repetitive impacts. Two types of plastic were repeatedly impacted under a constant load, and a tensile test was performed on the plastic material that was impacted. The tensile strength of PC plastic materials that received impact more than 2000 times was reduced by about 45 % and elongation was reduced by about 10 % when compared to impact free specimens. On the other hand, in ABS plastic, a reduction of tensile strength of about 20 % was observed at about 2,000 impacted specimen, but at about 20,000 repetitive impacted specimen, a tensile strength decrease of about 65 % was observed. And the elongation was reduced by 10 % due to the cyclic harding behavior of the material.

• The korean journal of orthodontics
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• v.36 no.5
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• pp.331-338
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• 2006

Objective: The purpose of this study was to evaluate whether the bond strength of polycarbonate brackets can be increased through surface treatment. Methods: One hundred polycarbonate brackets (Alice) were bonded to bovine incisors with light-cured adhesive. The bracket bases were treated with one of three methods; sandblasting, plastic conditioner application, and combined treatment with sandblasting and plastic conditioner. The brackets without any suraace treatment served as the control. The shear bond strength was tested with a universal testing machine, and failure pattern was assessed with the adhesive remnant index. Results: The shear bond strength in all experimental groups was higher than that of the control group (p < 0.001). The group treated with plastic conditioner after sandblasting showed statistically higher shear bond strength than the sandblasting only group to (p < 0.05). The group treated with plastic conditioner after sandblasting showed higher shear bond strength than plastic conditioner only group, but the difference was not statistically significant. Conclusion: The above results suggest that the surface treatments of polycarbonate bracket is mandatory to improve bond strength, and the most effective method is an application of plastic conditioner after sandblasting.

• Steel and Composite Structures
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• v.25 no.6
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• pp.671-684
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• 2017

Elastic-plastic shear buckling behaviors of the web-post in a Castellated Steel Beam (CSB) with hexagonal web openings under vertical shear force were investigated further using Finite Element Model (FEM) based on a sub-model, which took the upper part of the web-post under horizontal shear force to represent the whole web-post under vertical shear force. A simplified design method for the web-post elastic-plastic shear buckling strength was proposed based on simulation results of the sub-model. Proper boundary conditions were applied to the sub-model to assure that its behaviors were identical to those of the whole web-post. The equation to calculate the thin plate elastic shear buckling strength was adopted as the basic form to build the design equation for elastic-plastic buckling strength of the sub-model. Parameters that might affect the elastic-plastic shear buckling strength of the whole web-post were studied. After obtaining the vertical shear buckling strength of a sub-model through FEM, the shear buckling coefficient k can be obtained through the back analysis. A practical calculation method for k was proposed through curving fitting the parameter study results. The elastic-plastic shear buckling strength of the web-post calculated using the proposed shear buckling coefficient k agreed well with that obtained from the FEM and test results. And it was more precise than those obtained from EC3 based on the strut model.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.145-150
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• 2002

It has been well known that ductile fracture of steels is accelerated by triaxial stresses. The characteristics of ductile crack initiation in steels are evaluated quantitatively using two-parameters criterion based on equivalent plastic strain and stress triaxiality. It has been demonstrated by authors using round-bar specimens with circumferential notch in single tension that the critical strain to initiate ductile crack from specimen center depends considerably on stress triaxiality, but surface cracking of notch root is in accordance with constant strain condition. In order to evaluate the stress/strain state in the specimens, especially under dynamic loading, a thermal, elastic-plastic, dynamic finite element (FE) analysis considering the temperature rise due to plastic deformation has been carried out. This study provides the fundamental clarification of the effect of strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, loading mode and loading rate on critical condition to initiate ductile crack from notch root using equivalent plastic strain and stress triaxiality based on the two-parameter criterion obtained on homogeneous specimens under static tension. The critical condition to initiate ductile crack from notch root for strength mismatched bend specimens under both static and dynamic loading would be almost the same as that for homogeneous tensile specimens with circumferential sharp notch under static loading.

• Archives of Plastic Surgery
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• v.36 no.5
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• pp.538-542
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• 2009

Purpose: The successful wound healing means the scarless wound with adequate strength. It has been shown in vivo and in vitro that steroid retard the collagen synthesis. We studied the effect of steroid on the wound breaking strength in rats. Methods: 40 Sprague - Dawley rats were evenly assigned to two groups. One group was served as control, the other group was experimental. We made dorsal midline incision and closed the wound. In the experimental group, we medicated methylprednisolone (0.15 mg/g/day) for 1 week. Then, we compared the differences of the breaking strength and microscopic histology between control and experimental group at 2, 4, 6 and 8 week. Results: Up to 4 week, the breaking strength of the experimental group was markedly decreased than that of control group, while at 6 week the strength of experimental group attained to that of control group nearly. In histologic findings, control group demonstrated dense organization of collagen to experimental group at 4th week. Conclusion: In this experiment, steroid significantly inhibited the strength gain in wound at early period of the wound healing process. When using steroid after the surgery or the wound formation, it is desirable to administrate carefully and need thorough wound management to prevent delayed wound healing.

• Korean Journal of Materials Research
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• v.29 no.10
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• pp.603-608
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• 2019

Plastic waste is becoming a problem in various countries because of the difficulty of natural decomposition. One type is PET plastic(Polyethylene Terephthalate), which is often used as a bottle for soft drink packaging, and LDPE(Low Density Polyethylene), which is also widely used as a food or beverage packaging material. The use of these two types of plastic continuously, without good recycling, will have a negative impact on the environment. Building material waste is also becoming a serious environmental problem. This study aims to provide a solution to the problem of the above plastic waste and building material waste by making them into a mixture to be used as bricks. Research is carried out by mixing both materials, namely plastic heated at a temperature of $180-220^{\circ}C$ and building material waste that had been crushed and sized to 30-40 mesh with homogeneous stirring. The ratios of PET and LDPE plastic to building material waste are 9 : 1, 8 : 2, 7 : 3, 6 : 4 and 5 : 5. After heating and printing, density, water absorption and compressive strength tests are carried out. Addition of PET and LDPE plastic can increase compressive strength, and reduce water absorption, porosity and density. A maximum compressive strength of 10.5 MPa is obtained at the ratio of 6 : 4.

• The Journal of Korean Academy of Prosthodontics
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• v.34 no.3
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• pp.464-474
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• 1996

A principal advantage of a plastic tooth over a porcelain tooth should be its ability to bond to the denture base material. But plastic teeth could craze and wear easily, so more abrasion resistant plastic denture teeth have been developed. To resist abrasion, the degree of cross-linking was increased, but bonding to denture base meterial became more difficult. The purpose of this study was to evaluate the bond strength of plastic teeth and abrasion resistant teeth bonded to heat-curing, self-curing and light-curing denture base material. Denture tooth molds were chosen that had a>8mm diameter. The denture teeth was bonded to three denture base materials and then machined to the same dimensions. Three denture base materials were used as control groups. Prior to tensile testing, the specimens were thermocycled between $5^{\circ}C\;and\;55^{\circ}C$ for 1000cycles. Tensile testing was performed on an Instron Universal testing mechine. Experimental group ; plastic teeth(Justi Imperial)+heat-curing resin(Lucitone 199) plastic teeth(Justi Imperial)+light-curing resin(Triad) plastic teeth(Justi Imperial)+self-curing resin(Vertex SC) abrasion resistant teeth(IPN)+heat-curing resin(Lucitone 199) abrasion resistant teeth(IPN)+light-curing resin(Triad) abrasion resistant teeth(IPN)+self-curing resin(Vertex SC) Control group ; heat-curing resin(Lucitone 199) light-curing resin (Triad) self-curing resin(Vertex SC). The results were as follows : 1. The denture teeth bonded to heat-curing resin showed the cohesive failure and those bonded to the other resins showed adhesive failure. 2. Tensile bond strength of the plastic teeth bonded to self-curing resin was not significantly greater than bonded to light-curing resin(p>0.05). 3. Tensile bond strength of the abrasion resistant teeth bonded to self-curing resin was not significantly greater than bonded to light-curing resin(p>0.05). 4. Tensile bond strength of the plastic teeth to self-curing resin was not significantly different from that of the abrasion-resistant teeth(p>0.05). 5. Tensile bond strength of the plastic teeth to light-curing resin was significantly greater than that of the abrasion resistant teeth(p<0.01).