• Structural Engineering and Mechanics
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• v.84 no.3
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• pp.375-391
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• 2022

This paper discussed and analyzed the interfacial stress distribution characteristic of adjacent cracks in Carbon Fiber Reinforced Polymer (CFRP) plate strengthened concrete slabs. One un-strengthened concrete test beam and four CFRP plate-strengthened concrete test beams were designed to carry out four-point flexural tests. The test data shows that the interfacial shear stress between the interface of CFRP plate and concrete can effectively reduce the crack shrinkage of the tensile concrete and reduces the width of crack. The maximum main crack flexural height in pure bending section of the strengthened specimen is smaller than that of the un-strengthened specimen, the CFRP plate improves the rigidity of specimens without brittle failure. The average ultimate bearing capacity of the CFRP-strengthened specimens was increased by 64.3% compared to that without CFRP-strengthen. This indicites that CFRP enhancement measures can effectively improve the ultimate bearing capacity and delay the occurrence of debonding damage. Based on the derivation of mechanical analysis model, the calculation formula of interfacial shear stress between adjacent cracks is proposed. The distributions characteristics of interfacial shear stress between certain crack widths were given. In the intermediate cracking region of pure bending sections, the length of the interfacial softening near the mid-span cracking position gradually increases as the load increases. The CFRP-concrete interface debonding capacity with the larger adjacent crack spacing is lower than that with the smaller adjacent crack spacing. The theoretical calculation results of interfacial bonding shear stress between adjacent cracks have good agreement with the experimental results. The interfacial debonding failure between adjacent cracks in the intermediate cracking region was mainly caused by the root of the main crack. The larger the spacing between adjacent cracks exists, the easier the interfacial debonding failure occurs.

• Textile Coloration and Finishing
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• v.35 no.3
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• pp.159-168
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• 2023

Polyolefin elastomer (POE) is widely used in a variety of applications, particularly in the manufacture of composites, due to its excellent mechanical properties, chemical resistance, and flexibility. However, POE has a high processing temperature, which causes damage to the fiber during the manufacturing process when impregnating the fiber. Therefore, ethylene vinylacetate (EVA), which has a low melting point and excellent adhesion properties, is blended with POE to reduce the processing temperature, and POE-g-MAH (Polyolefin elastomer-grafted-maleic anhydride) is used as a compatibilizer to further improve the POE/EVA blend properties. The compatibility of POE/EVA blends is observed by SEM, and the interaction between each polymer is confirmed by DSC and FT-IR. In addition, the effect of adding the compatibilizer is analyzed through mechanical properties such as tensile strength and elongation. The optimal content of compatibilizer for POE/EVA blends considering physical properties and moldability is sought, and 20 phr is determined to be the most appropriate.

• Corrosion Science and Technology
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• v.22 no.6
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• pp.419-428
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• 2023

Seawater has been used to cool devices in nuclear power plants. However, the pipes used to transport seawater are vulnerable to corrosion; hence, the inner side of pipelines is coated with an epoxy layer as prevention. Upon coating damage, the pipe becomes exposed, and corrosion progresses. The major cause is widely known as cavitation corrosion, causing the degradation of mechanical properties. In this study, corroded specimens were prepared using cavitation and immersion methods to clarify the degradation trend of mechanical properties with corrosion. Three different types of epoxy coatings were used, and accelerated cavitation procedures were composed of amplitudes of 15 ㎛, 50 ㎛, and 85 ㎛ for 2 h, 4 h, and 6 h. The immersion periods were 3 and 6 weeks. We conducted instrumented indentation tests on all degradation samples to measure mechanical properties. The results showed that higher cavitation amplitudes and longer cavitation or immersion times led to more degradation in the samples, which, in turn, decreased the yield strength. Of the three samples, the C coating had the highest resistance to cavitation and immersion degradation.

• Geomechanics and Engineering
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• v.36 no.5
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• pp.511-525
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• 2024

Underground openings significantly affect the mechanical stability of underground spaces and create damaged zones. This study investigated the acoustic emission (AE) characteristics associated with the formation of damaged zones around circular openings. Uniaxial compression experiments were conducted on three types of rock specimens, namely, granite (GN-1 and GN-2), gabbro (GB), and slate (SL), containing a circular opening. AE and digital image correlation (DIC) techniques were used to monitor and evaluate the damaged zones near the circular openings. The AE characteristics were evaluated using AE parameters, including count, energy, amplitude, average frequency, and RA value. The DIC results revealed that the estimated diameters of the damaged zones of GN-1, GN-2, GB, and SL were 1.66D, 1.53D, 1.49D, and 1.9D, respectively. The average displacements at the surface of the damaged zones for these specimens were 0.814, 0.786, 0.661, and 0.673 mm, respectively, thus demonstrating a strong correlation with Young's modulus. The AE analysis with DIC revealed that tensile failure occurred in the direction parallel to the maximum compression axis as the load increased. Thus, this study provides fundamental data for a comprehensive analysis of damaged zones in underground openings and will facilitate the optimization of rock engineering projects and safety assessments thereof.

• Structural Engineering and Mechanics
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• v.91 no.2
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• pp.211-225
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• 2024

Soft bending actuators have gained significant interest in robotic applications due to their compliance and lightweight nature. Their compliance allows for safer and more natural interactions with humans or other objects, reducing the risk of injury or damage. However, the nonlinear behaviour of soft actuators presents challenges in accurately predicting their bending motion and force exertion. In this research, a new comprehensive study has been conducted by employing a developed 3D finite element model (FEM) to investigate the effect of geometrical and material parameters on the bending behaviour of a soft pneumatic actuator reinforced with Kevlar fibres. A series of experiments are designed to validate the FE model, and the FE model investigates the improvement of actuator performance. The material used for fabricating the actuator is RTV-2 silicone rubber. In this study, the Cauchy stress was expanded for hyperelastic models and the best model to express the stress-strain behaviour based on ASTM D412 Type C tensile test for this material has been obtained. The results show that the greatest bending angle was achieved for the semi-elliptical actuator made of RTV2 material with a pitch of 1.5 mm and second layer thickness of 1 mm. In comparison, the maximum response force was obtained for the semi-elliptical actuator made of RTV2 material with a pitch of 6 mm and a second layer thickness of 2 mm. Additionally, this research opens up new possibilities for development of safer and more efficient robotic systems that can interact seamlessly with humans and their environment.

• Nuclear Engineering and Technology
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• v.56 no.5
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• pp.1887-1894
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• 2024

Fatigue strength of the structural materials of lead-cooled fast reactors (LFRs) and accelerator-driven systems (ADS) may be degraded in liquid metal (Lead or lead-bismuth eutectic (LBE)) environments. The fatigue crack growth (FCG) data of structural materials in liquid LBE are necessary for damage tolerance design, safety assessment and life management of key equipment. A novel monitoring system for fatigue crack length was designed on the compliance method and the monitor technology of crack opening displacement (COD) of CT specimens by the linear variable differential transformers (LVDT) system. It can be used to predict the crack length by monitoring the COD of CT specimens in harsh high-temperature liquid LBE using a LVDT system. The prediction accuracy of this system was verified by FCG experiments in room temperature air and liquid LBE at 150, 250 and 350 ℃. The first results obtained in the FCG test for T91 steel in liquid LBE at 350 ℃ are presented.

• Journal of Chest Surgery
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• v.43 no.3
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• pp.235-245
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• 2010

Background: Our goal was to evaluate anti-calcification effects of decellularization and diverse fixing methods including preincubation of the bovine pericardium with ethanol. We also assessed changes in mechanical properties. Material and Method: Harvested bovine pericardium was decellularized with 0.25% sodim dodecysulfate and then treated with 5 methods of fixation: (1) 0.5% glutaraldehyde (GA) for 14 days, (2) 0.5% GA for 5 days, 2% GA for 2 days and 0.25% GA for 7 days, (3) 0.5% GA for 5 days, 2% GA for 2 days, 0.25% GA for 7 days, and then 70% ethanol for 2 days, (4) 0.5% GA for 5 days, a mixture of 2% GA and 70% ethanol for 2 days, and 0.25% GA for 7 days, (5) 0.5% GA for 5 days, a mixture of 2% GA, 65% ethanol, and 5% octanediol for 2 days and then 0.25% GA for 7 days. All treated bovine pericardia were tested for histological variables, lipid content, and mechanical properties including tensile strength and thermal stability. A total 10 kinds of differently treated bovine pericardia were implanted into rat subdermis and harvested 8 weeks later. Harvested pericardia were evaluated for calcium content. Result: No protein denaturation was observed microscopically after decellularization. There was a 32% mean decrease in tensile strength index after decellularization in the bovine pericardium group fixed. Octanediol preincubation attenuated the decrease in tensile strength and maintained thermal stability. TG and cholesterol were not affected by decellularization but were decreased by organic solvent. Calcium content was decreased after decellularization, and organic solvent preincubation decreased calcification in the non-decellularized bovine pericardium group. Conclusion: Decellularization and organic solvent preincubation have anti-calcification effects but decellularization may cause mechanical instability. A method of decellularization and fixation that does not cause damage to matrices will be needed for evaluation of the next step in using tissue-engineering for replacement of cardiac valves.

• Korean Journal of Heritage: History & Science
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• v.46 no.3
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• pp.212-228
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• 2013

Stone cultural heritages are repaired by the use of metal stiffeners. The problem is that this type of repair has been based on the experience of workers without specific guidelines and has caused various problems. This is to suggest the structural reinforcement and behavioral characteristics of metal rods to minimize the secondary damage of materials and have the specimens tested and verified to establish the guidelines on how to insert metal stiffeners. When only epoxy resin is applied to the cut surface, only 70% of the properties of the parent material are regenerated and it is required to structurally reinforce the metal stiffener for the remaining 30%. The metal rod is under the structural behavior after the brittle failure of stone material and the structural behavior does not occur when the metal stiffener is below 0.251%. When it accounts for over 0.5%, it achieves structural reinforcement, but causes secondary damage of parent materials. The appropriate ratio of metal stiffener for the stone material with the strength of $1,500kgf/cm^2$, therefore, should be between 0.283% and 0.377% of the cross section of attached surface to achieve reversible fracture and ductility behavior. In addition, it is more effective to position the stiffeners at close intervals to achieve the peak stress of metal rod against bending load and inserting the stiffener into the upper secions is not structurally supportive, but would rather cause damage of the parent material. Thus, most stiffeners should be inserted into the lower part and some into the central part to work as a stable tensile material under the load stress. The dispersion effect of metal rods was influenced by the area of reinforcing rods and unrelated to their diameter. However, it ensures stability under the load stress to increase the number of stiffeners considering the cross section adhered when working on large-scale structures. The development length is engineered based upon the diameter of stiffener using the following formula: $l_d=\frac{a_tf_y}{u{\Sigma}_0}$. Also, helically-threaded reinforcing rods should be used to perform the behaviors as a structural material.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.45 no.2
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• pp.185-198
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• 2019

Human tissue undergoes aging by the oxidant damage via structural change and its physical properties. The skin aging process is well known and many evaluations have been conducted. However, studies on hair aging were relatively few and thus care for aging hair is difficult. This study aims to fabricate an aging hair and identify anti-aging effect with known ingredient in anti-aging. First of all, physical properties of aging hair of age 60s by physiologically intrinsic factors were compared to those of the hair made by various extrinsic factors such as several chemical reactions and iteration numbers of the treatments. The extrinsic aging hair of this study relates to the less amount of lipid and to the hair of perm treated once accordingly, wherein several physical properties, preferably comprise roughness and tensile strength, present a novel concept of the intrinsic aging hair. The penetration of peptide into the aging hair was leading the extrinsic hair towards more structurally directed a younger hair. In addition to the structural change, the penetration of the peptide enhanced texture and tensile strength of the aging hair. These patterns have been also found in addition of propolis. For the first time, these qualitative studies exhibit that indeed our extrinsic aging hair well describes the anti-aging efficacy as a receptor for a cross-linker and the ingredients of human hair.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.369-379
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• 2012

The collapse of concrete structures by extreme loads such as impact, explosion, and blast from terrorist attacks causes severe property damage and human casualties. Concrete has excellent impact resistance to such extreme loads in comparison with other construction materials. Nevertheless, existing concrete structures designed without consideration of the impact or blast load with high strain rate are endangered by those unexpected extreme loads. In this study, to improve the impact resistance, the static and impact behaviors of concrete beams caste with steel fiber reinforced concrete (SFRC) with 0~1.5% (by volume) of 30 mm long hooked steel fibers were assessed. Test results indicated that the static and impact resistances, flexural strength, ductility, etc., were significantly increased when higher steel fiber volume fraction was applied. In the case of the layered concrete (LC) beams including greater steel fiber volume fraction in the tensile zone, the higher static and impact resistances were achieved than those of the normal steel fiber reinforced concrete beam with an equivalent steel fiber volume fraction. The impact test results were also compared with the analysis results obtained from the single degree of freedom (SDOF) system anaysis considering non-linear material behaviors of steel fiber reinforced concrete. The analysis results from SDOF system showed good agreement with the experimental maximum deflections.