• Journal of Adhesion and Interface
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• v.14 no.2
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• pp.95-100
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• 2013

In this study, a series of hot-melt pressure sensitive adhesives (HMPSAs) based on metallocene polyolefin (me-PO) were prepared to investigate their possibility of replacing the HMPSAs based on styrenic block copolymers (SBCs). In addition, to optimize the performance of HMPSAs based on me-PO, several tackifiers having different softening point and molecular weight were evaluated. To achieve the HMPSAs which can satisfy the Dahlquist Criterion, hot melts required over 10% of process oil. To obtain the HMPSAs having low viscosity which can be applied by a spraying type applicator, secondary polymer having relatively low crystallinity was required. And, tackifier having high molecular weight attributed to increasing the cohesive strength of me-PO based HMPSAs.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.221-227
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• 2001

Both strength and stiffness of RC structures strengthened by a steel plate greatly increase and however, their ductility might not be sufficient because premature failures usually occur at the adhesive-concrete interface. In this study, Mohr-Coulomb criterion was adopted to examine the bonding failure mechanism, and the diagonal shear bonding test, the direct shear bonding test, and the flexural test on RC beams strengthened by a steel plate were carried out to measure the bonding properties. It is found from the experimental and numerical results that the cohesive strengths of epoxy-concrete interfaces are ranging from 50 kgf/㎠ to 70 kgf/㎠ when the friction angle is 45°. Bonding failure loads can be predicted by applying the bonding properties to the structural analysis of RC beams strengthened by steel plate. By considering them in the design of strengthened beams, the premature failure would be effectively prevented.

• Composites Research
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• v.36 no.3
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• pp.154-161
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• 2023

This study explored the feasibility of replacing a metal link with a carbon fiber/epoxy composite link and assessed its capacity to withstand a given load condition using failure criteria. The micromechanics of failure (MMF) criterion was employed to predict the failure mode of the composite material, and mechanical tests were conducted to obtain reference strength parameters for MMF. The findings revealed that the stress distribution was concentrated near the hole, and weaknesses were found around the hole and at the end of the link under bending conditions. Based on the failure index, matrix tensile failure was predicted at the end of the link, and fiber compression failure occurred near the hole. The methods and results obtained from this study can provide valuable guidelines for assessing the safety of composite materials under specific load conditions when replacing metal parts with carbon fiber/epoxy composites to achieve weight reduction.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.138-144
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• 1989

It has been very important in various industry fields to improve the fatigue strength characteristics of bearings such as bearing life, fatigue limit, etc., because such poor properties could result in shortening the machinery life as well as in decreasing the accuracy. However, no successful heat treatment criterion seems to be available at present. In this study, the effect of the $170^{\circ}C\times120min$ tempering cycles repeated after $380^{\circ}C\times80min$ oil quenching for $800^{\circ}C$ spheroidizing-annealed bearing steel (STB2) as base metal on the $120^{\circ}C$ high temperature rotary bending fatigue strength characteristics were investigated, including the effects on hardness, Charpy impact value and micro-structure, in order to seek for the best heat treatment condition finally. The important results obtained are as follows : 1) The optimal cycle of tempering so that the fatigue strength .sigma. could become the highest was the 4th cycle. And it is confirmed that this $\sigma_{F}$ is about 6 times more increased than that of base metal, and about 1.3 times more increased than the case of the 1 cycle tempered. 2) As a result of the investigation for the effects of tempering cycles on hardness, the hardness at the tempering number of 2 thru 5 cyles was not decreased severely ; only about 10% decrease from those of the quenched and 1 cycle tempered case. Such hardness is equivalent to $H_{R}$/C61-62 with no bad effect on anti-abrasion of bearing steel. 3) In the case of 2 thru 5 cycle tempering as well as 1 cycle tempering, the impact value was not so improved comparing with the case of quenching, but an increase of 5 to 10% could be expected at least. 4) It was experimentally confirmed that the control of the mechanical properties improvement such as fatigue strength and fatigue life for bearing steels could be possible by the number of tempering cycles.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.638-638
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• 1989

It has been very important in various industry fields to improve the fatigue strength characteristics of bearings such as bearing life, fatigue limit, etc., because such poor properties could result in shortening the machinery life as well as in decreasing the accuracy. However, no successful heat treatment criterion seems to be available at present. In this study, the effect of the $170^{\circ}C\times120min$ tempering cycles repeated after $380^{\circ}C\times80min$ oil quenching for $800^{\circ}C$ spheroidizing-annealed bearing steel (STB2) as base metal on the $120^{\circ}C$ high temperature rotary bending fatigue strength characteristics were investigated, including the effects on hardness, Charpy impact value and micro-structure, in order to seek for the best heat treatment condition finally. The important results obtained are as follows : 1) The optimal cycle of tempering so that the fatigue strength .sigma. could become the highest was the 4th cycle. And it is confirmed that this $\sigma_{F}$ is about 6 times more increased than that of base metal, and about 1.3 times more increased than the case of the 1 cycle tempered. 2) As a result of the investigation for the effects of tempering cycles on hardness, the hardness at the tempering number of 2 thru 5 cyles was not decreased severely ; only about 10% decrease from those of the quenched and 1 cycle tempered case. Such hardness is equivalent to $H_{R}$/C61-62 with no bad effect on anti-abrasion of bearing steel. 3) In the case of 2 thru 5 cycle tempering as well as 1 cycle tempering, the impact value was not so improved comparing with the case of quenching, but an increase of 5 to 10% could be expected at least. 4) It was experimentally confirmed that the control of the mechanical properties improvement such as fatigue strength and fatigue life for bearing steels could be possible by the number of tempering cycles.

• Journal of Bio-Environment Control
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• v.19 no.4
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• pp.210-216
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• 2010

This study was carried out to investigate the plant growth of various foliage plants affected by the nutrient solution strength. Ficus benjamina, Hedera helix, Philodendron tatei, Rhapis excelsa, Spathiphyllum spp. were used in this experiment. The Sonneveld solution was diluted to 0, 1/4, 1/2, and 1 folds and applied through a subirrigation system. Plant height and width, leaf number, leaf area, fresh and dry weights of shoots were measured to compare the responses to the different treatments. The required amounts for nutrients were different among the various foliage plants. The growth of Ficus and Philodendron was improved as the nutrient solution strength got higher, but that of Hedera and Spathiphyllum showed the best growth in the lower nutrient solution strength of 1/4 and 1/2 folds. The growth of Rhapis was improved in the nutrient solution strength of 1 fold but the other treatments did not affect on plant growth. N, P, and K were the most important nutrients that had influence on the growth of the foliage plants in this study. There was not an accurate criterion for fertilization and irrigation to each foliage plant. Moreover, the foliage plants grew slowly during the early stage and this period must be shortened for commercial production. Therefore, the experiment was executed to make up these defects. The plants applied with proper strength of Sonneveld solution grew faster and had better quality.

• Journal of Family Resource Management and Policy Review
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• v.26 no.2
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• pp.53-70
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• 2022

This study aimed to develop a scale to measure the family strength of single-parent families. We analyzed the everyday life and demands of single-parent families using the theory of family strength to draw 78 items that encompass family basis, relationships, roles, social networks and family culture. Using a sample of 286 single-parent families through an online survey platform, we examined the factor structure of the items and selected 48 items based on the results of the factor analysis. Reliability, criterion and construct validity were also examined. The final scale comprised of five domains ; basis, parents' role, work-life balance, social network, lifestyle and household management. This scale can be used as an assessment measure of the family strength of single-parent families for consulting, case management and suggesting various programs in the field. This merit will help enhance the quality of programing for single-parent families at the Healthy Family Support Center and the development of family strength scales for various types of families.

• Journal of Family Resource Management and Policy Review
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• v.27 no.1
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• pp.25-39
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• 2023

This study aims to analyze the differences in the strength of single-parent families based on family characteristics. Using a sample of 267 female single parents, we explore the factors that impact family strength. We found that several variables impact the strength of families headed by a female single parent: the length of time members had lived together as a single-parent family, co-residents, interactions with ex-spouses, full-time work, and household income. Based on these findings, we suggest that the length of time that single-parent families have lived together is an important criterion for planning and evaluating the family policies and services offered by healthy family support centers. Furthermore, in the context of family resource management, family policies and programs that address time management and family life planning for full-time single parents should be developed and implemented.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.27 no.1
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• pp.1-10
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• 1982

Degree of grain shattering which is of varietal character is an important determinant for the magnitude of field loss of grains during harvest and threshing. Seven Indica \times Japonica progeny varieties and four Japonica varieties were subjected to measurements of tensile strength of grains, degree of grain shattering when panicles were dropped at 1.5m above concrete floor, and moisture content of grains (wet basis) during a period 35 to 63 days after heading. In addition, two varieties were tested for the relation of tensile strength of grains to the magnitude of field loss of grains in actual binder harvest. The 11 varieties differed conspicuously in tensile strength of grains and the degree of grain shattering: the weakest average tensile strength of grains of a variety was about 90g and the strongest about 250g with varying standard deviation of 30 to 60g. Three Indica \times Japonica varieties and one Japonica variety shattered I to 30% of the grains under the falling test. The threshold tensile strength of grains allowing grain shattering was estimated to be 180g on average for a sampling unit of 10 panicles, but only the grains having tensile strength weaker than 98g within the samples shattered. A decrease in average tensile strength by 10g below the threshold value corresponded to an increase of 3 to 5% in grain shattering. Most varieties did not change appreciably the tensile strength of grains and degree of grain shattering with delay in time of harvest and showed a negative correlation between the tensile strength and the moisture content of grains. The average tensile strength of grains was negatively correlated linearly with field loss in binder harvest. The average tensile strength for zero field loss in binder harvest was estimated to be 174g and a decrease in the average tensile strength by 10g corresponded to an increase of 40kg per hectare in field loss of grains. Instead of the average tensile strength of grains, the percentage of grains having tensile strength weaker than 100g is recommended as a criterion for the estimation of field loss of grains during harvesting operations as well as a basis of variety classification for grain shattering, since the standard deviation of tensile strength of grains varies much with variety and time of harvest, and individual grains having tensile strength stronger than 98 did not shatter practically.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.305-314
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• 2012

This paper presents the quantitative damage assessment of granite taken from KAERI Underground Research Tunnel using acoustic emission (AE). The results determined showed the crack initiation and crack damage stress occurred at 48%, 72% of uniaxial compressive strength (UCS) and until the applied stress level was reached the crack damage stress, the damage degree was 0.06. When the applied stress exceeded 80%, 90% of UCS, the damage degree were 0.34, 0.06 and which were similar to those obtained from axial deformation modulus. The simply regression analysis was used to interpret the relationship of the two damage assessment techniques and the two were highly correlated ($R^2$=0.90). Therefore, damage degree based on the AE energy and mohr-coulomb failure criterion were adopted to predict the mechanical properties. As results, the axial deformation modulus, rock strength, internal friction angle, and cohesion of KURT rock were reduced 6%, 12%, 7%, and 3% until the applied stress was 70% of UCS. But when the applied stress reached 90% of UCS, the results were more reduced 69%, 72%, 62%, and 24%, respectively.