두께와 노치생성방법에 따른 플라스틱 수지의 충격강도 변화에 관한 연구

김현(Hyun Kim),이대섭(Dae Seop Lee),임재수(Jae Soo Lim),류민영(Min Young Lyu) 한국고분자학회 2012 폴리머 Vol.36 No.1

제품의 소형화와 경량화 추세에 따라 부품의 두께가 얇아지는 경향이 있다. 이러한 소형 및 경량 제품의 중요한 설계요소는 소재의 충격강도이다. 충격강도는 재료 고유의 물성값으로 기하학적 형상에 의존하지 않고 일정한 값을 가져야 한다. 그러나 충격강도 시험 시 시편의 두께에 따라 강도의 차이를 보이고 노치(notch)의 생성방법과 노치형상에 따라서도 민감도를 보인다. 본 연구에서는 시편의 두께와 노치형상 및 노치의 생성방법에 따른 충격강도를 알아보았다. 또한 노치의 각도와 노치에 대한 충격 방향에 따른 충격강도도 관찰하였다. 이를 위해 엔지니어링 플라스틱인 PC, ABS, 그리고 POM에 대하여 Izod 충격시험을 수행하였다. 그 결과 실험한 모든 수지에서 두께가 얇아질수록 충격강도가 높아지는 경향을 보였는데 PC수지가 가장 크게 증가하였다. PC수지는 두께가 두꺼울 때는 취성파괴를 보였는데 두께가 얇을 때는 연성파괴 양상을 보였다. 몰드노치 시편이 밀링노치 시편에 비해 충격강도가 높았고, 역방향 노치가 정방향 노치보다 충격강도가 높았다. 본 연구에서 실험한 수지 중에서 노치의 민감성은 PC가 가장 컸으며 다음이 POM, ABS순으로 나타났다. The impact strength of material is considered the most important design factor for small and light products. Impact strength is a unique material property, thus the impact strength should not depend upon the geometry of specimen. However it varies according to specimen thickness, notching method, and notch shape. In this study, the variations of impact strength have been investigated according to thickness, notch shape, and notching method of specimen. Engineering plastics such as PC, ABS and POM have been used in this study. Experimental results showed impact strength increased as thickness decreasesd. PC showed the highest increment of impact strength when the thickness was thin. Fractured section of PC showed brittle fracture behavior when the specimen was thick. However it showed ductile fracture behavior when it was thin. The impact strength of in-mold notched specimen showed higher than that of milling notched specimen. PC showed the highest notch sensitivity among the materials used in this experiment.

Prediction of multiaxial fatigue life for notched specimens of titanium alloy TC4

Z. R. Wu,X. T. Hu,Z. X. Li,Y. D. Song 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.5

Both the proportional and nonproportional multiaxial fatigue tests were conducted on two kinds of notched specimens of titanium alloy TC4. The multiaxial fatigue critical area of notched specimen is considered as the location experiencing the maximum damage. It is unsatisfactory to predict the multiaxial fatigue life with the local stress and strain in the fatigue critical area. The critical distance concepts are employed in the multiaxial life prediction method for notched specimens. The proposed method was checked by the test data of TC4 notched specimens. The prediction results are almost within a factor of three scatter band of the test results.

Al6061-T6 평판 시편의 노치반경과 두께가 파괴 메커니즘에 미치는 영향

두샤오(Xiao Du),왕량(Liang Wang),최낙삼(Nak-Sam Choi) 대한기계학회 2021 大韓機械學會論文集A Vol.45 No.3

Al6061-T6 합금의 연성파괴는 네킹의 발생 시에 생기는 삼축인장응력과 관계가 있다. 노치 반경과 두께에 따른 시편 표피와 내부의 응력상태가 달라진다. 본 연구에서는 두께 4 mm, 8 mm의 평판으로 노치 없는 시편(un-notched), 노치 반경이 큰 시편(L-notched, R228.1 mm), 노치 반경이 작은 시편(S-notched, R2.5 mm)을 제작하였다. 슬립라인 이론(slip line theory), 타원기준(ellipse criterion), 유한요소법(FEM), 2D 디지털 이미지 상관법(2D-DIC)을 이용하여 노치 반경과 두께에 따른 응력상태와 파괴위치를 해석하였으며 주사 전자현미경(SEM) 관찰을 병행하여 파괴 양상을 관찰하였다. 노치반경이 작을수록 응력집중으로 인해 시편 내부에 형성한 높은 삼축인장응력이 파괴를 주도하였다. 두께가 커지면 파괴는 삼축인장응력과 최대전단응력에 의한 혼합모드의 파괴거동을 보였다. The fracture behavior of Al6061-T6 alloy is related to stress triaxiality formation during the local necking process of the specimen. Distribution of triaxial tensile stress varies with different notch radii and specimen thickness. In this study, plate specimens (un-notched), specimens with large notch radius (L-notched, R228.1 mm), and specimens with small notch radius (S-notched, R2.5 mm) were made of aluminum alloy plates (thickness 4 mm, 8 mm). Slip line theory, the ellipse criterion, finite element method (FEM), and 2D digital image correlation (2D-DIC) were used to find the effect of notch radii and specimen thickness on stress state distributions and initial fracture mechanisms. A scanning electron microscope (SEM) was used to observe the initial fracture surface. For a small notch radius causing high stress concentration, the fracture began at a site close to the notch tip due to high triaxial tensile stress. With increasing specimen thickness, the fracture surface showed a mixed mode failure behavior caused by both the triaxial tensile stress and maximum shear stress.

양쪽에 노치들을 가진 시험편의 재료 강도에 대한 평가 및 검증

이정호,조재웅 한국기계기술학회 2016 한국기계기술학회지 Vol.18 No.5

Composite materials have the strong durability and light weight as inhomogeneous material. These material are manufactured by combining and maximizing the advantage of each material. Among these various materials, stainless steel, aluminum and brass has been used generally. Prior to using, the preparatory experiments are demanded in order to obtain the material strengths. In this study, the tensile tests are carried out with the specimens of stainless steel, aluminum and brass. These tensile specimens of same standards are made with the notches at both sides of specimen. When the forced displacement of about 11 mm proceeds in case of stainless steel specimen, the maximum load of 31000 N is shown simultaneously with the fracture of specimen. When the forced displacement of about 6 mm proceeds in case of aluminum specimen, the maximum load of 20600 N is shown simultaneously with the fracture of specimen. When the forced displacement of about 7 mm proceeds in case of brass specimen, the maximum load of 25000 N is shown. In this study, the finite element analysis as ANSYS program is carried out in order to verify these experimental results. The experimental and analysis results are similarly shown each other. Through the result of this study, the analysis data with no experiments are thought to be trustworthy as the tensile experimental data.

Modeling of axisymmetric slow crack growth of high-density polyethylene with circular notched bar specimen using crack layer theory

Wee, J.W.,Choi, B.H. Pergamon Press ; Elsevier Science Ltd 2016 International journal of solids and structures Vol.97 No.-

Because of the characteristic of high triaxial stress of a circular notched bar (CNB) specimen under tensile loads, it is a promising candidate for accelerated durability testing of high-density polyethylene (HDPE). To understand the slow crack growth (SCG) behavior of HDPE using a CNB specimen, it is practically important to base the evaluation of the SCG model using a CNB specimen on the concept of fracture mechanics. In this study, the SCG kinetics of HDPE with a CNB specimen is modeled on the basis of the concept of an axisymmetric crack layer (CL) system. CL theory is applied to the modeling of the axisymmetric SCG considering the geometry of the CNB specimen. Green's functions of the stress intensity factor and crack opening displacement of the CNB specimen are calculated in order to simulate the CL kinetics. The obtained Green's functions are also utilized to compute the thermodynamic forces for both the crack growth and the CL growth, and a generalized CL growth algorithm is developed. A parametric study of several key input parameters is conducted for validation of the developed CL model. In addition, actual SCG generated experimentally is simulated using the developed model, and it is found that the actual test results can be successfully simulated using the developed CL model.

노치를 지닌 CFRP와 금속 인장 시험편들의 강도 및 내구성 평가

이정호,조재웅 한국기계기술학회 2016 한국기계기술학회지 Vol.18 No.6

The composite material has the strong durability and light weight as inhomogeneous material. Nowadays, CFRP composite has been noticed as the light weight, high strength and long fatigue life. This study has been carried actively. In this study, the properties of tensile strengths of CFRP, stainless steel are analyzed, and compared each other. In order to secure the data, the tensile specimens with notches of same size by using CFRP, and stainless steel are manufactured and experimented. When the forced displacement of about 11.5 mm proceeds in case of stainless steel specimen, the maximum load of 31000 N is shown simultaneously with the fracture of specimen. When the forced displacement of about 6 mm proceeds in case of CFRP specimen, the maximum load of 16000 N is shown. So, the structural safety becomes highest at CFRP specimen among these specimens. In this study, the finite element analysis is carried out in order to compare with the experimental results. It is verified that the experimental and analysis results are similarly shown each other. Through the result of this study, it is thought that the simulation analysis data with no experiments are trustworthy at using as the real tensile experimental data.

Correction of constraint loss in fracture toughness measurement of PCVN specimens based on fracture toughness diagram

Choi, Shin-Beom,Chang, Yoon-Suk,Kim, Young-Jin,Kim, Min-Chul,Lee, Bong-Sang 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.3

The aim of this paper is to suggest an approach to generate master curves by using miniature specimens, especially pre-cracked Charpy V-notched (PCVN) specimen, made of SA508 carbon steel. Firstly, fracture toughness diagram is derived from comparing finite element analyses results with the fixed mesh size at crack tip between standard compact tension and PCVN specimens. To compensate the constraint effects from different geometry, further examination based on the fracture toughness diagram was performed. In this context, a scale factor to deal with specimen size effects is proposed by statistically manipulating the numerical analysis data. Finally, the proposed scale factor is applied to calculate reference temperature which affects on the master curve. We expect that the approach can be applicable to compensate the geometrical constraint effects on fracture toughness of SA508 carbon steel when the PCVN specimen is used.

Size Effect on Axial Compressive Strength of Notched Concrete Specimens

Yi, Seong-Tae,Kim, Jin-Keun Korea Concrete Institute 2002 KCI concrete journal Vol.14 No.1

In this study, size effect tests were conducted on axial compressive strength of concrete members. An experiment of Mode I failure, which is one of two representative compressive failure modes, was carried out by using dimensionally proportional cylindrical specimens (CS). An adequate notch length was taken from the experimental results obtained from the compressive strength experiment of various initial notch lengths. Utilizing the notch length, specimen sizes were then varied. In addition, new parameters for the modified size effect law (MSEL) were suggested using Levenberg-Marquardt's least square method (LSM). The test results show that size effect was apparent for axial compressive strength of cracked specimens. Namely, the effect of initial notch length on axial compressive strength size effect was apparent.

The Effect of Temperature on Stress Corrosion Cracking of Al Brass under Flow

( Uh Joh Lim ),( Hae Kyoo Jeong ) 한국부식방식학회 2003 Corrosion Science and Technology Vol.2 No.3

Fracture behavior of nuclear grade graphite under mixed mode I-II

Eung-Seon Kim 한양대학교 세라믹연구소 2013 Journal of Ceramic Processing Research Vol.14 No.2

Mixed mode I and mode II fracture toughness values of five grades of nuclear graphites were measured at room temperature using a centrally notched disk specimen. The specimens were compressed diametrically with a crosshead speed of 0.125 mm/ min in ambient air. The fracture loads of the nuclear graphites decreased as the notch inclination angle increased under mixed mode I-II loading. The nuclear grade graphites with the higher bulk density and coarser coke particles showed higher mode I and mode II fracture toughness. The ratios of KIIc/KIc were in the range of 1.4 ~ 1.5 regardless of the coke type and size