Papers by Keyword: Pre-Strain

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Authors: Jong Hyun Baek, Young Pyo Kim, Woo Sik Kim, Chang Sung Seok
Abstract: Pipelines for natural gas transmission may be subjected to plastic deformation by the outside force such as ground subsidence, ground liquefaction, cold bending and mechanical damage. Plastic deformation affects the tensile properties and fracture toughness. Tensile test, Crack tip opening displacement test and Charpy impact test were conducted on an API 5L X65 pipe to investigate the mechanical properties of pipeline subjected to plastic deformation. Axial tensile pre-strain up to approximately 10% was applied to plate-type tensile specimens cut from the API 5L X65 pipe prior to mechanical testing. Tensile test revealed that the yield strength and the tensile strength increased with increasing tensile pre-strain. However, the CTOD and Charpy impact energy values for crack initiation decreased with increasing tensile pre-strain.
Authors: Sansot Panich
Abstract: Bending and hemming process are used in automotive industries for assembling the car body panel.The main failure mechanism under bending loads is the intercrystalline fracture. This is due to the fact that the Forming Limit Curve (FLC) describes first occurrence of membrane instability and no material failure in consequence of an intercrystalline fracture at bending.The FLC fails to predict the formability in hemming processes since difference in failure mechanism. A new failure criterion, the so-called Bending Limit Curve (BLC) has been developed. In this work, the left hand side BLCs are experimentally determined for Advanced High Strength Steel grade DP1000, Stainless Steel grade SUS430 and Deep Drawing Steel grade SPCC having a thickness of 1.0 mm. The influence of various bending radii and level of pre-strain on the bending strains are investigated and discussed by using the Three Point Bending Test. Bendability of investigated materials are evaluated by using optical strain measurement system GOM-Aramis to determine maximal achievable bending strain on the specimens. The developed left hand side BLCs were found to be higher level than conventional FLCs. The bigger bending radius established lower bending limit strain. The higher bending strain was obtained from the higher pre strain level.
Authors: Heru Sukanto, Triyono, Nurul Muhayat
Abstract: Stiffened sheet metal structure where sheet metal is reinforced by frame has been claimed as the most effective structure because it has low volume and weight. It is generally applied to large car body structure such as bus and train body. Frame and sheet are commonly joined by welding process. Due to the local heating of welding, distortion or deformation will occur in this structure. To mitigate this distortion, new method called stretching technology was proposed in this work. In this method, sheet was stretched to certain pre-strain, kept in this condition and then welded to frame. Special equipment powered by hidroulic system was designed to support this method. Low carbon steel SPAC specimens with dimension of 400mm, 1824mm and 3mm in width, length and thick respectively were prepared to evaluate the method. Hidroulic power was controlled to meet the sheet pre-strain variations of 0.00%, 0.05%, 0.10% and 0.15%. The distortion of the specimen was measured by dial indicator with mesh point of 50mm and shown in 2D contour chart. The study results revealed that the welding process on the sheet without pre-strain had the highest distortion of 8.34mm while that with pre-strain of 0.05% provided the lowest distortion of 3,3mm or 60% lower than without pre-strain specimen. The pre-strain of 0.10% and 0.15% produced the sheet distortion of 7.05mm and 7.9mm respectively. The excessive pre-strain was an ineffective method to mitigate the welding distortion because the reverse tension force of sheet would destroy the weld joint when the hydraulic force was released.
Authors: Ilana B. Timokhina, Elena V. Pereloma, Peter D. Hodgson
Abstract: The effect of pre-straining (PS) and bake-hardening (BH) on the microstructure and mechanical properties has been studied in C-Mn-Si TRansformation Induced Plasticity (TRIP) steels after: (i) thermomechanically processing (TMP) and (ii) intercritical annealing. The steels were characterised before and after PS/BH by transmission electron microscopy (TEM), X-ray diffraction (XRD), and tensile tests. The main microstructural differences were the higher volume fraction of bainite and more stable retained austenite in the TMP steel. This led to a difference in the strain-hardening behavior before and after BH treatment. The higher dislocation density in ferrite and formation of microbands in the TMP steel after PS and the formation of Fe3C carbides between the bainitic ferrite laths during BH for both steels also affected the strain-hardening behavior. However, both steels after PS/BH treatment demonstrated an increase in the yield and tensile strength.
Authors: Gao Feng Quan, Ying Bo Zhang, Zhao Ming Liu
Abstract: Mg Alloys Are the Lightest Structural Alloys with Excellent Castability and Machinability as Well as Highest Specific Strength and Stiffness. According to their Hexagonal close Packed Crystal Lattice there Is an Urgent Requirement of Mechanical Property Evaluation Method for Industrial Application, Particularly to Wrought Mg Alloys. Cyclic Loading Is a Very Popular Mode for Most Structural Application Situations. Recent Development of Fatigue Examination of Extruded Profile Has Shown that Mg Alloys Show Not so Ideal Fatigue Property. so that the Further Detailed Study on Cyclic Loading for Plastic Deformed Mg Alloys Is Needed. Tension-Tension Fatigue Tests Were Conducted on Pre-Strained AZ31 Mg Alloys that Produced by Rolling and Extruding Procedures. the Results Show that the Compressive Plastic Deformation Leads to Reduction of Fatigue Life/limit Significantly. SEM Analysis on Fatigue Fracture Surfaces Indicates that the Fatigue Cracks Initiate in the Surface or Sub-Surface of Dramatically Deformed Zones. the Microstructure Analysis Reveals that the Pre-Strain Brings More Abundant Twinning Bands with the Increase in Pre-Strain. the Decrease in Fatigue Life Demonstrates Also some Critical Feature with the Pre-Strain Level.
Authors: Wen Xian Sun, S. Nishida, Nobusuke Hattori, X.L. Yue
Abstract: In the present study, fatigue tests have been performed to study the effect of pre-strain on fatigue properties of NHH (New Head-Hardened) rail. The objectives of this study were: (1) to observe the microscopic behavior of specimens during pre-strain process, (2) to research the influence of pre-strain on fatigue strength of NHH rail and (3) to investigate initiation and propagation behavior of the fatigue crack. The results showed that plastic pre-strain decreased the fatigue strength of NHH rail; fatigue limits had no obvious variation among the different pre-strain ratios. Fatigue cracks initiated in the microscopic cracking or slip lines that were originated in the pre-strain process and propagated from these sites in the later fatigue test.
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