• Advanced Composite Materials
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• 제17권2호
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• pp.139-156
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• 2008

This study aims to characterize the dynamic tensile strength of unidirectional carbon/epoxy composites. Two different carbon/epoxy composite systems, the unidirectional T700S/2500 and TR50S/modified epoxy, are tested at the static condition and the strain rate of $100\;s^{-1}$. A high-strain-rate test was performed using a tension-type split Hopkinson bar technique with a specific fixture for specimen. The experimental results demonstrated that both tensile strength increase with strain rate, while the fracture behaviors are quite different. By the use of the rosette analysis and the strain transformation equations, the strain rate effects of material principal directions on tensile strength are investigated. It is experimentally found that the shear strain rate produces the more significant contribution to strain rate effect on dynamic tensile strength. An empirical failure criterion for characterizing the dynamic tensile strength was proposed based on the Hash-in's failure criterion. Although the proposed criterion is just the empirical formula, it is in better agreement with the experimental data and quite simple.

• Journal of Welding and Joining
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• 제21권7호
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• pp.49-58
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• 2003

It has been well known that ductile fracture of steel is accelerated by triaxiality stresses. The characteristics of ductile crack initiation in steels are evaluate quantitatively using two-parameter criterion based on equivalent plastic strain and stress triaxiality. Recently, the characteristics of critical crack initiation of steels are quantitatively estimated using the two-parameter, that is, equivalent plastic strain and stress triaxiality, criterion. This study is paid to the fundamental clarification of the effect of geometrical heterogeneity and strength mismatching, which can elevate plastic constraint due to heterogeneous plastic straining, and loading rate on critical condition to initiate ductile crack using two-parameter. Then, the crack initiation testing were conducted under static and dynamic loading. To evaluate the stress/strain state in the specimens especially under dynamic loading, thermal elastic-plastic dynamic FE-analysis considering the temperature rise was used. The result showed that the critical global strain to initiate ductile fracture in specimens with strength mismatch under various loading rate cu be estimated based on the local criterion, that is two-parameter criterion obtained on homogeneous specimens under static tension, by mean of FE-analysis taken into account accurately both strength mismatch and dynamic loading effects on stress/strain behavior.

• 대한통합의학회지
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• 제10권4호
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• pp.57-69
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• 2022

Purpose : The purpose of this study was to investigate the effect of ankle strengthening exercise combined with sling-assisted gluteus medius strengthening on ankle instability score, and static and dynamic balance ability, muscle strength in adults in their 20s with chronic ankle instability. Methods : Twenty-eight adults in their 20s with chronic ankle instability were recruited. After screening test, they were randomized through R studio program as an experimental group (n=14) to apply an ankle strengthening exercise combined with sling-assisted gluteus medius strengthening and a control group (n=14) to apply ankle strengthening exercise. The intervention lasted two times a week for 6 weeks. To compare the intervention effects, the Cumberland ankle instability tool (CAIT) score, static and dynamic balance ability, and muscle strength of lower extremities were measured. Results : The experimental group showed a significant increase in pre and post-intervention Cumberland ankle instability tool (CAIT) score, static and dynamic balance ability, and muscle strengt (p<.05). The control group showed a significant increase in pre and post-intervention CAIT score, dynamic balance ability, and muscle strength (p<.05). The experimental group showed a significant increase in CAIT score, dynamic balance ability, and muscle strength compared to the control group (p<.05), and showed a high effect size. Conclusions : The results of this study confirmed that ankle strengthening exercise combined with sling-assisted gluteus medius strengthening on people with chronic ankle instability the possibility that it could be effective in improving ankle instability and improving dynamic balance ability, and strength by movement. Although additional research is needed to increase the number of participants due to the small sample size, it is hoped that this study will be an optimistic clinical protocol for people with chronic ankle instability.

• 대한물리의학회지
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• 제17권2호
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• pp.83-93
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• 2022

PURPOSE: This study examined the comparative effects of an ankle sensorimotor training program combined with hip strengthening exercise (ASTPCHSE) and ankle sensorimotor training program (ASTP) alone on muscle strength, static balance, and dynamic balance in individuals with functional ankle instability. METHODS: Sixteen research participants with functional ankle instability were enrolled in this study. The participants were divided randomly into the ankle sensory motor training program group and the ankle sensory motor training program combined with the hip strengthening exercise group. Each group performed a series of exercise programs two times per week for four weeks. The Cumberland ankle instability tool (CAIT) was used to measure the participants' functional ankle instability. A Balance trainer 4 was applied to assess the static and dynamic balance, and a Primus RS multimodal dynamometer was used to evaluate the muscle strength. RESULTS: No significant differences in static balance, dynamic balance, and muscle strength were found between the ASTP and ASTPCHSE groups (p > .05). On the other hand, the dynamic balance and muscle strength improved in the ASTP and ASTPCHSE groups after the intervention (p < .05). The static balance was not enhanced in both groups after the intervention (p > .05). CONCLUSION: Ankle exercise and an ankle sensorimotor training program combined with hip strengthening exercise are effective in improving muscle strength and dynamic balance in individuals with ankle instability. On the other hand, there are no meaningful differences between ankle exercise and ankle and hip combined exercise.

• 한국전문물리치료학회지
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• 제1권1호
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• pp.67-74
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• 1994

Our purpose of this study was to determine the most effective cool-down exercise. The recovery times of dynamic strength after isometric and isotonic cool-down exercise were measured immediately post cool-down exercise, 30 seconds later and 60 seconds later in 30 normal, healthy men from 19 to 29 years, using dumbells(Model, Iron). The recovery time of dynamic strength had a significant positive correlation with isotonic and isometric cool-down exercise using the Chi-square method (p<0.01). Sources of significant differences were determined by the Wilcoxon signed-ranks test (p<0.01). The isometric cool-down exercise significantly shortened the recovery time of dynamic strength. We suggest that the isometric cool-down exercise may be more effective than isotonic cool-down exercise in shortening the recovery time of dynamic strength.

• The Journal of Korean Physical Therapy
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• 제33권5호
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• pp.224-230
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• 2021

Purpose: The purpose of this study was to investigate the effects of the fascia distortion model (FDM), one of the fascia treatments, on unstable ankle subjects. This was done through the chronic ankle instability tool (CAIT) questionnaire on maximum isometric muscle strength, proprioception, dynamic balance, and maximum angle. Methods: An experiment was conducted using the chronic ankle instability tool questionnaire on males and females in their twenties who suffered from ankle instability. Before the experiment, maximum isometric strength, proprioceptive, dynamic balance, and maximum angle were measured. The fascia distortion model was applied and then measurements were taken again to compare and analyze the changes. Analysis was carried out using the paired t-test. Results: After applying the fascia distortion model, maximum isometric strength, proprioceptive, dynamic balance, and maximum angle significantly improved (p<0.05). Conclusion: This study found that the fascia distortion model method was effective in improving maximum isometric strength, proprioceptive, dynamic balance, and maximum angle. The results suggest that the fascia distortion model method is a new intervention that could be used for subjects with chronic ankle instability.

• Geomechanics and Engineering
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• 제18권5호
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• pp.471-480
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• 2019

The constructions of engineering structures such as airports, highways and railway on clayey soils may create many problems. The economic losses and damages caused by these soils have led researchers to do many studies using different chemical additives for the stabilization of them. Lime is a popular additive used to stabilize the clayey soils. When the base course is stabilized by mixing with an additive, inevitable delays may occur during compaction due to reasons like insufficient workers, breakdown of compaction equipment, etc. The main purpose of this study is to research the effect of compaction delay time (7 days) on the strength, compaction, and dynamic properties of a clay soil stabilized with lime content of 0, 3, 6, 9, 12 and 15% by dry weight of soil. Compaction characteristics of these mixes were determined immediately after mixing, and after 7 days from the end of mixing process. Within this context, unconfined compressive strength (UCS) under the various curing periods (uncured, 7 and 28 days) and dynamic triaxial tests were performed on the compacted specimens. The results of UCS and dynamic triaxial tests showed that delayed compaction on the strength of the lime-stabilized clay soil were significantly effective. Especially with the lime content of 9%, the increase in the shear modulus (G) and UCS of 28 days curing were more prominent after 7 days mellowing period. Because of the complex forms of hysteresis loops caused by the lime additive, the damping ratio (D) values differed from the trends presented in the literature and showed a scattered relationship.

• 한국지진공학회논문집
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• 제12권5호
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• pp.23-29
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• 2008

강도한계 이선형 단자유도 시스템의 지진 하중 하에서의 동적 불안정에 대해 연구하였다. 강도한계 이선형 이력 모델은 철골 모멘트 골조의 이력거동을 가장 잘 모사한다. 단자유도 시스템의 동적 불안정을 판단하기 위해 붕괴 강도비를 사용하였고, 이것은 붕괴가 일어날 때의 항복강도 저감계수이다. 단단한 지반에서 측정된 240개의 지진을 이용하고 고유주기, 강성 경화 기울기, 음강성 기울기, 연성 그리고 $2{\sim}20%$의 감쇠비를 변수로 하여 강도한계 이선형 단자유도 시스템의 붕괴 강도비의 평균과 편차 값들을 구할 수 있도록 통계 분석을 하였다. 비선형 회귀분석을 통해 강도한계 이선형 단자유도 시스템의 붕괴 강도비의 평균과 표준편차를 계산할 수 있는 식을 구하였다. 제안한 식을 이용하여 붕괴 강도비의 확률적 분포를 구하였고, 실제 값과 비교하여 제안한 식의 정확성을 입증하였다.

• The Journal of Korean Physical Therapy
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• 제31권2호
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• pp.94-102
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• 2019

Purpose: This study examined the effects of trunk control rehabilitation robot training (TCRRT) on the dynamic balance, lower extremity strength, gait ability and pain for bipolar hemiarthroplasty. Methods: Hemiarthroplasty (n=28) patients participated in this study. The subjects were randomized into two groups: trunk control rehabilitation robot training group and control group. Results: The TCRRT group showed significantly more improvement in the MFRT, MMT, 10MWT, TUG, and VAS compared to that before intervention (p<0.05). In addition, all tests were significantly greater in the experimental group than in the control group. Conclusion: These results suggest that TCRRT is feasible and effective for improving the dynamic balance, lower extremity strength, gait ability, and pain efficacy after bipolar hemiarthroplasty.

• 한국정밀공학회지
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• 제13권11호
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• pp.124-131
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• 1996

The dynamic material property of Mn-B ally high-strength steel is investigated through the rod impact test which is one of simple test methods for the analysis of the material behavior under high-strain-rate. Rod impact test is performed to produce the deformed shape of rod and analyzed by the one-dimensional theory based on conservation law and the two-dimensional hydrocode AUTODYN-2D. The dynamic yield stress is determined and compared with the static yield stress to investigate the strain-rate sensitivity of Mn-B alloy high-strength steel.