Dong-Gi Lee

Creep and tensile properties of press molding joined GMT-sheets

GMT-sheet is used in automobile bumper with high rigidity and strength, and its joining strength is influenced by lap length, one of the joined molding conditions. Fracture strength was calculated by dividing fracture load with cross-sectional area. Total five repeated measurements were made to obtain the average value. Tensile test was conducted at room temperature for 10 specimens. In addition, the effect of compression ratio on creep and tensile performance during lap joined molding was discussed. With increasing lap length, the lap joining efficiency of GMT-sheet was increased. However, higher compression ratio reduced the joining efficiency. Creep test on GMT-sheet showed abrupt fracture without tertiary creep. This can be explained by the weak thermal resistance of the resin. If GMT-sheet was exposed to high temperature for a long time, it was easily failed by external force.

Fiber Orientation State Depending on the Injection Mold Gate Variations during FRP Injection Molding

Because of orientation and separation, injection molded products are heterogeneous and anisotropic. These heterogeneousness and anisotropy have a vast influence on mechanical properties of molding material and product characteristics. It is well known that fiber orientation state in fiber-reinforced polymeric composite has a profound effect on dynamic qualities like intensity, rigidity, and etc. To measure the fiber orientation of injection molded products weld part, we first X-rayed moldings and recognized this photo by using an image scanner. Then, image processing method, which uses intensity difference in measuring fiber orientation state, is applied. Through these procedures, we can analyze the influence of moldings fiber orientation state according to mold gate changes. Fiber orientation is related mainly with the mold gate positions than with fiber content or mold temperature. When the distance from the gate increases, by matrix and reinforcements flow speed differences, fiber orientation occurred. As diversion flow occurred at the end of fluid flow, fiber oriented at a right angle to the flow, and this is the same effect of weld line formation.

Effect of Fiber Orientation on the Tensile Strength in Fiber-Reinforced Polymeric Composite Materials

The study for strength calculation of one way fiber-reinforced composites and the study measuring precisely fiber orientation distribution were presented. However, because the DB that can predict mechanical properties of composite material and fiber orientation distribution by the fiber content ratio was not constructed, we need the systematic study for that. Therefore, in this study, we investigated what effect the fiber content ratio and fiber orientation distribution have on the strength of composite sheet after making fiber reinforced polymeric composite sheet by changing fiber orientation distribution with the fiber content ratio. The result of this study will become a guide to design data of the most suitable parts design or fiber reinforced polymeric composite sheet that uses the fiber reinforced polymeric composite sheet in industry spot, because it was conducted in terms of developing products. We studied the effect the fiber orientation distribution has on tensile strength of fiber reinforced polymeric composite material and achieved this results below. We can say that the increasing range of the value of fiber reinforced polymeric composite’s tensile strength in the direction of fiber orientation is getting wider as the fiber content ratio increases. It shows that the value of fiber reinforced polymeric composite’s tensile strength in the direction of fiber orientation 90° is similar with the value of polypropylene’s intensity when fiber orientation function is J= 0.7, regardless of the fiber content ratio. Tensile strength of fiber reinforced polymeric composite is affected by the fiber orientation distribution more than by the fiber content ratio.

Manufacturing of GFRP Sheet Using Plain Weaving Method

최근 자동차 관련 기술개발의 동향은 자동차 연비향상 등을 위한 경량화, 자원재활용을 위한 리사이클링, 부품의 모듈화, 차체 수명연장, 안정성 향상, 배기가스의 정화, 소음방지, 전기 및 하이브리드 자동차 등에 대한 폭 넓은 연구개발 투자가 이루어지고 있다. 자동차의 경량화 방안은 우수한 물성을 갖는 경량재료의 개발과 기존재료의 제조방법 개선을 통한 기계적 성질을 향상시키는 방법 등이 있으며, 이를 위해 사용되는 재료로 알루미늄(Al) 합금, 마그네슘(Mg) 합금, 티타늄(Ti) 합금, 철강재료 등의 금속재료 외에 플라스틱 소재에 유리섬유로 강화한 플라스틱 복합재료 등이 있다. 플라스틱 복합재료는 모재와 강화재의 종류 및 형태에 따라 기계적 물성이 변화한다. 각종 플라스틱 복합재료 중에서 열가소성수지를 모재로 한 재료는 리사이클이 가능하고, 최종처리로써 소각도 용이하다. 이 재료는 비중이 작기 때문에 자동차 구조 부품의 경량화에 유효하고 비강도, 비강성, 충격강도 등의 기계적 특성이 뛰어나다.

Generalized Stability Condition for Descriptor Systems

In this paper, we propose a generalized index independent stability condition for a descriptor systemwithout any transformations of system matrices. First, the generalized Lyapunov equation with a specific right-handed matrix form is considered. Furthermore, the existence theorem and the necessary and sufficient conditions for asymptotically stable descriptor systems are presented. Finally, some suitable examples are used to show the validity of the proposed method.

TENSILE STRENGTH OF GLASS FIBER-REINFORCED PLASTIC BY FIBER ORIENTATION AND FIBER CONTENT VARIATIONS

For unidirectional composite material, there is a theoretical mixture rule equation to calculate the strength of composite from properties of matrix and fiber content. However, the equation for tensile strength with the fiber content and the fiber orientation is not available. Therefore, this study was investigated what affect fiber content and fiber orientation have on the strength of composites. Glass fiber-reinforced plastic by changing fiber orientation and fiber content was made. Tensile strength of 0° direction of composites increased being proportional fiber content and fiber orientation function as change from isotropy (J=0) to anisotropy (J=1). But, tensile strength of 90° direction by separation of fiber filament decreased when tensile load is imposed for width direction of reinforcement fiber length direction. In this study, empirical equation to estimate tensile strength out of fiber orientation and fiber content was proposed.

Effects of Molding Condition on Surface Unevenness of GFRP Composites in Compression Molding

We have investigated the unexpected phenomena on the surface of molded GFRP composites. The major cause of the unevenness, as a result of which the surface becomes rough, is a shrinking of the matrix in the process of holding pressure and cooling temperature. The higher holding pressure load in a molding process and the lower demolding temperature in an annealing experiment, the better GFRP composites moldings improved its appearance. In addition, by taking the holding pressure and demolding temperature into consideration, we evaluate the process that causes the surface unevenness and the variation in the fiber projection height.

An Analysis of the Characteristics of SPG Bridges Using NExT and ERA for Real-Time Monitoring

The paper analyzes the characteristics of a Steel Plate Girder (SPG) bridge structure using Natural Excitation Technique (NExT) and Eigensystem Realization Algorithm (ERA). This analysis is to estimate how the long measuring time which causes difficulty in a real-time monitoring can be reduced and so to accurately identify the physical characteristics of a structure. It also attempts to assess its applicability to a real bridge structure. To explain more in detail, we make Hankel Matrix from Cross Correlation, and then the characteristics of a structure are identified using ERA. The suggested algorithm, in this paper, is applied to the SPG bridges and the results are shown in the good correlation. And we estimate whether it is applicable in real-time measuring, and analyze some problems and suggest the alternatives to them. Introduction The dynamic characteristics of a structure contain useful information about its structural condition, and so vibration testing can be considered as a global non-destructive structural real-time monitoring technique [1][2]. In a real-time monitoring system, however, it is not easy to excite large structures such as bridges and buildings, which has thereby become an important issue. As input excitation devices for civil structures, people have used rotating mass vibrators, electro-hydraulic vibrators, and impact testing based on a suspended mass. However, those forced excitation devices are not only very expensive but also may cause some possible damage to the structure. In order to avoid such problems, an ambient vibration testing is suggested in which the input excitation signals are not forced or controlled. This ambient vibration testing is effectively and conveniently used to measure the vibration response while the structure is under any traffic loads, winds, and earthquakes. This paper proposes a structural real-time monitoring method for civil structures. Instead of using the input excitation devices mentioned above, this method employs the natural excitation technique (NExT) developed by James et al. [3][4]. This approach does not need to specify the excitation source, so it is applicable to any problems in general where excitation occurs all the time or excitation is not structurally measurable. The eigensystem realization algorithm (ERA) is then used to determine estimates of the structure modal parameters [5][6]. Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 2012-2017 doi:10.4028/www.scientific.net/KEM.270-273.2012

Analysis of temperature distribution during tension test of glass fiber reinforced plastic by fiber orientation variation.

In this paper, analysis of temperature distribution by fiber orientation variation under tension test was proposed through IR thermography camera. Lock-in method, which is one of technique in IR thermography camera to measure minute change in temperature, was utilized to monitor temperature distribution and change during crack propagation. Method to analyze of temperature distribution by fiber orientation variation under tension test of GFRP via IR thermography camera was suggested. At the maximum stress point, temperature was significantly increased. As shown previously, specimen with shorter fracture time showed abrupt increment of temperature at the maximum stress point. Specimen with longer fracture time displayed increment of temperature after the maximum stress point.

Strength and efficiency during lap joining molding of GMT-sheet

In order to substitute and recycle the existing automobile parts for GMT‐Sheet, researches on the effects of GMT‐Sheet on the establishment of precise joining strength, joining condition that are lap length of joining part, compression ratio, and closure speed must be carried out but until now, there is almost no case of systematic researches on joint of GMT‐Sheet. Therefore, as there are many obstacles in joining of GMT‐Sheet molding products or in production of stable molding products, the researches on these issues are required. Because of this, it is reality that GMT‐Sheet is only applied to parts of newly developed automobiles instead of substituting the existing automobile parts. In this study, materials with each different fiber content ratio and fiber orientation state were used in the study for decision of molding condition of GMT‐Sheet and the condition of lap joining. Clarify joining strength and lap joining efficiency during high temperature. Compression press lap joining molding of GMT‐Sheet ...