• International Journal of Concrete Structures and Materials
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• 제8권2호
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• pp.117-128
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• 2014

Numerous investigations of RC beams strengthened in shear with externally-bonded (EB) fibre-reinforced polymer (FRP) sheets, plates and strips have been successfully conducted in recent years. These valuable studies have highlighted a number of influencing parameters that are not captured by the design guidelines. The objective of this study was: (1) to highlight experimentally and analytically the influential parameters on the shear contribution of FRP to RC beams strengthened in shear using EB FRP sheets and strips; and (2) to develop a set of transparent, coherent, and evolutionary design equations to calculate the shear resistance of RC beams strengthened in shear. In the experimental part of this study, 12 tests were performed on 4,520-mm-long T-beams. The specimens were strengthened in shear using carbon FRP (CFRP) strips and sheets. The test variables were: (1) the presence or absence of internal transverse-steel reinforcement; (2) use of FRP sheets versus FRP strips; and (3) the axial rigidity of the EB FRP reinforcement. In the analytical part of this study, new design equations were proposed to consider the effect of transverse-steel in addition to other influential parameters on the shear contribution of FRP. The accuracy of the proposed equations has been verified in this study by predicting the FRP shear contribution of experimentally tested RC beams.

• Steel and Composite Structures
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• 제20권4호
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• pp.833-849
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• 2016

Pre-stressing of existing structures using steel cables, FRP cables or FRP laminates has been successfully tried in the past. Retrofitting of beams using pre-stressed laminates does not utilize the full strength of the FRP due to de-bonding of the laminates before the fibre fracture. In the present study attempt has been made to overcome this problem by replacing the FRP laminates by the FRP sheets. In the present paper the effect of initial damage level and pre-stress level on strength, stiffness, cracking behaviour and failure mode of girders retrofitted using pre-stressed CFRP sheets has been studied. The results indicate that rehabilitation of initially damaged girders by bonding pre-stressed CFRP sheets improves the flexural behaviour of beams appreciably. However, it has been observed that with increase in pre-stressing force the load carrying capacity of the girders increases up to a particular level up to which the mode of failure is fibre fracture. Thereafter, the mode of failure shifts from fibre fracture to de-bonding and there is no appreciable increase in load carrying capacity with further increase in pre-stressing force.

• Journal of Welding and Joining
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• 제15권4호
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• pp.42-62
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• 1997

Resistance spot welding has been widely used in the sheet metal joining processes because of its high productivity and convenience. Recently, automobile industries are trying to replace partly steel sheets with aluminum alloy sheets. Among currently produced aluminum alloys, Al alloy sheets of Al-Mg-Si(6000 series) are being tested. Especially, 6000 series are the most probable substitute in view of strength and weldability. In this paper, an attempt was made to apply resistance spot welding to joining of dissimilar sheet metals (KS6383+SCPZn or KS6383+SHCP). An effort was made to balance heating rate in the Al alloy with that in the steel sheets by increasing electrode tip diameter. Although resistance spot welding of Al alloy sheet and sheet metals does not produce desirable nugget, it proved to have reasonable strength if optimal weld condition is found by tensile-shear strength and fatigue life test. Since spot weld joints in automobile are always experiencing repeated load, spot welding methodology proposed in this paper is found to be not suitable to automobile body manufacturing.

• 소성∙가공
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• 제29권1호
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• pp.5-10
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• 2020

Heat treatment conditions of 88.5% asymmetrically cold rolled oxygen free copper (OFC) sheets have been studied to obtain an equiaxed fine microstructure with a grain size of less than 10 ㎛. The commercial OFC sheets with the thickness of 10 mm were asymmetrically cold rolled by using equal speed asymmetric rolling (ESAR) processes and total rolling reduction. The thickness of the rolled sheets were 88.5% and 1.15 mm, respectively. An equiaxed fine microstructure of OFC sheets with a grain size of 6.0 ㎛ were obtained when the asymmetrically cold rolled OFC sheets were heat treated at 180℃ for 40 minutes. The tensile strength of the asymmetrically cold rolled specimen increased from 217.6 MPa to 396.1 MPa, while the elongation of the specimen asymmetrically cold rolled and heat treated increased from 29.0% to 66.9% along with an 8% increase of the tensile strength.

• 소성∙가공
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• 제29권1호
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• pp.27-36
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• 2020

The Goss texture component of {110}<001> is well known as one of the best texture components to improve the magnetic properties of electrical steel sheets. The small amount of the Goss texture component is obtained at the surface of the steel sheet by shear deformation due to friction between the steel sheet and the roll during conventional symmetric rolling. This study aims to identify a method to obtain high intensity of the Goss texture component not only at the surface but in the whole layer of the steel sheet by shear deformation of asymmetric rolling. Low carbon steel sheets, which have different initial texture, were asymmetrically rolled by about 50%, 70%, and 80%. The pole figures of the top, center, and bottom layers of the initial and asymmetrically rolled low carbon steel sheets were measured by an X-ray diffractometer. Based on the measured pole figures of these samples, the intensities of the main texture components were analyzed for the initial and asymmetrically rolled low carbon steel sheets. As a result, the initial low carbon steel sheet with the γ-fiber component showed a higher intensity of the Goss texture component in the whole layer than the steel sheet with other texture components after asymmetric rolling.

• 소성∙가공
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• 제20권2호
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• pp.99-103
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• 2011

Many parameters influence the frictional behavior of steel sheet during stamping. The contact pressure between a die and a sheet during stamping is one of them. Thus, this parameter is investigated for high strength steel (HSS) sheets, which are widely used for auto body panels due to their potential for weight reduction. Since HSS extend the limits of contact pressure for mild steel, the effect of this parameter on friction cannot be ignored. To investigate the influence of contact pressure on the frictional behavior of steel sheets, a flat type of friction test was conducted on three different steel sheets under various contact pressures. For bare steel sheets, the curve representing the relationship between contact pressure and friction coefficient exhibits a U shape. Coated steel sheets show a similar tendency except at low contact pressure. For these materials, when the contact pressure is very low, the friction coefficient slightly increases with pressure before it starts to decrease. The test results show that the effect of contact pressure on frictional behavior of steel sheet is not negligible even for contact pressures that are lower than the strength of HSS sheet.

• 소성∙가공
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• 제19권8호
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• pp.502-507
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• 2010

The physical and mechanical properties and formability of sheet metals depend on preferred crystallographic orientations (texture). In this research work, the texture development and formability (plastic strain ratios) of AA1050 Al alloy sheets after 3 and 10 passes of asymmetric rolling and subsequent heat treatment were investigated. The plastic strain ratios of 10 passes asymmetrically rolled and subsequent heat treated samples are 1.3 times higher than those of the initial AA1050 Al alloy sheets. The ${\Delta}r$ of 10 passes of asymmetrically rolled and subsequent heat treated samples is 1/30 times lower than those of the initial AA1050 Al alloy sheets. The plastic strain ratios of 10 passes of asymmetrically rolled and subsequent heat treated Al sheets are higher than those of 3 passes ones. These results could be attributed to the formation of $\gamma$-fiber, ND//<111>, and the other texture components by means of asymmetric rolling in Al sheets.

• 전기학회논문지P
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• 제58권2호
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• pp.190-195
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• 2009

Thin-gauged 3% silicon steel sheets having a highly grain-oriented texture have been developed as a core material for applications of middle-frequency (400 Hz ${\sim}$ 10 kHz) devices. The newly developed sheets with a tension coating showed an excellent reduction in iron loss at 400 Hz (iron loss at 1.0 T and 400 Hz = 4.677 W/kg, iron loss at 1.5 T and 400 Hz = 9.742 W/kg) due to high magnetic induction, $B_{10}$(measured induction at 1000 A/m), of over 1.9 T. In cases of frequencies below 400 Hz, magnetic induction, $B_{10}$, of the sample plays a major role to reduce its iron loss as excitation induction increases, whereas, in case of frequency of 1 kHz, thickness dependence becomes dominant due to a lower iron loss at relatively thinner sample. The sheets with a high magnetic induction, therefore, are favorable for high excitation induction (over 1.0 T) and low excitation frequency (below 400 Hz) applications, whereas the sheets that can reduce eddy current loss by reducing thickness or domain wall width are advantageous for low excitation induction (below 1.0 T) and high excitation frequency (around 1 kHz) applications.

• 한국자동차공학회논문집
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• 제17권4호
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• pp.48-54
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• 2009

The demand for formable high-strength steel (HSS) sheets has recently increased to reduce the weight of automotive bodies. The 340MPa (Tensile Strength) grade steel sheets are widely used for body inner and outer panels. Especially, super formable 340MPa grade steel sheets with high r-value have an excellent deep drawability compared with the other 340MPa grade steel sheets. It is very available for a part such as rear floor, center floor and dash panels used conventional mild steels up to now. We developed a super formable HSS by optimization of chemical composition, texture control and heat treatment control. It has good mechanical properties with excellent formability (tensile strength: 343MPa, elongation: 41.1% and $\bar{r}=2.1$).

• Advances in nano research
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• 제8권4호
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• pp.265-276
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• 2020

A study that primarily focuses on nonlocal strain gradient plate model for the sole purpose of vibration examination, for graphene sheets under linearly variable in-plane mechanical loads. To study a better or more precise examination on graphene sheets, a new advance model was conducted which carries two scale parameters that happen to be related to the nonlocal as well as the strain gradient influences. Through the usage of two-variable shear deformation plate approach, that does not require the inclusion of shear correction factors, the graphene sheet is designed. Based on Hamilton's principle, fundamental expressions in regard to a nonlocal strain gradient graphene sheet on elastic half-space is originated. A Galerkin's technique is applied to resolve the fundamental expressions for distinct boundary conditions. Influence of distinct factors which can be in-plane loading, length scale parameter, load factor, elastic foundation, boundary conditions, and nonlocal parameter on vibration properties of the graphene sheets then undergo investigation.