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1
Vilotic, Dragisa, Sergei Alexandrov, Aljosa Ivanisevic, and Mladomir Milutinovic. "Reducibility of Stress-Based Workability Diagram to Strain-Based Workability Diagram." International Journal of Applied Mechanics 08, no. 02 (2016): 1650022. http://dx.doi.org/10.1142/s1758825116500228.
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The strain-based and stress-based workability diagrams are often used to predict the initiation of ductile fracture in metal forming. The strain-based workability diagram is restricted to free surface fracture and postulates that the initiation of fracture is independent of the strain path. It is shown in the present paper that under these conditions the strain-based workability diagram is identical to the stress-based workability diagram. Using an available stress-based workability diagram the strain-based workability diagram is found in a much larger domain in the space of two in-surface principal strains as compared to the typical domain covered by standard tests used to determine strain-based workability diagrams. Two feasible tests are designed to determine the complete strain-based workability diagram.
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Budden, P. J. "Failure assessment diagram methods for strain-based fracture." Engineering Fracture Mechanics 73, no. 5 (2006): 537–52. http://dx.doi.org/10.1016/j.engfracmech.2005.09.008.
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Lomunov, A. K., T. N. Yuzhina, L. Kruszka, and W. W. Chen. "DEFORMING AND FRACTURE OF LINDEN AND PINE UNDER INTENSIVE DYNAMIC IMPACTS." Problems of strenght and plasticity 82, no. 1 (2020): 43–51. http://dx.doi.org/10.32326/1814-9146-2020-82-1-43-51.
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The paper presents the results of dynamic tests under compression of two wood species: linden and pine under loading along and across the fibers. Dynamic tests were carried out using the modified Kolsky method with the realization of multi-cycle loading of the sample during one test. As a result, strain diagrams were obtained for uniaxial stress state taking into account additional loading cycles The use of the multi-cycle loading mode made it possible to obtain a significantly greater degree of the sample deformation than with traditional single-cycle loading. To create a pulse load, a gas gun was used. According to the experimental results, dynamic deformation diagrams were obtained, as well as ultimate strength and deformation characteristics, fracture energy for linden and pine were determined depending on the cutting angle of the samples and the strain rate. A strong anisotropy of the properties of the tested materials is observed: the samples have the greatest strength when a load is applied along the fibers, and the least - across the fibers. A positive effect of the strain rate is noted. The module of the load branch is non-linear and, as a rule, is smaller than the module of the unload branch (while maintaining the integrity of the sample). The nature of the deformation and fracture of the samples strongly depends on the angle of cutting-out. At cutting angle across the fibers, the deformation diagram after reaching a certain threshold value is close to an ideally plastic diagram. At cutting angle along the fibers, the initial portion of the diagrams is close to linear, i.e. elastic deformation takes place. However, after reaching a certain value (“yield strength”), the diagram becomes nonlinear. This kind of behavior takes place in those experiments in which the destruction of the samples occurs. For both wood species, there is a significant excess of energy absorption by samples cut and tested along the fibers, compared with samples cut and tested across the fibers.
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Mironov, Vladimir I., Olga A. Lukashuk, and Ivan S. Kamantsev. "Experimental Study of Strain-Softening Stage in Materials." Materials Science Forum 946 (February 2019): 276–81. http://dx.doi.org/10.4028/www.scientific.net/msf.946.276.
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Physical theory of reliability is based on research into degradation processes of various origins which take place in a material of a stressed construction. Experimental evaluation of parameters carried out for such processes is a practically important problem by itself. One of the approaches to solving this problem is related to the studies into the stage of material softening due to deformation. This paper analyzes the issues of experimental validation of material softening properties in terms of a phenomenological approach to the problem of structural fracture. Results of deformation analysis for the “machine – model specimen” system, using catastrophe theory are used to form requirements for carrying out experiments which investigate the softening stage of materials. The success of such experiments – which should include recording a branch descending to zero on a computer diagram – is possible when small specimen, made from structurally heterogeneous materials, are strained in a sufficiently rigid testing machine. Thus, the conditions for manifestation of the softening stage connect properties of the material with properties of the load-applying system. Therefore, the material's limiting state – preceding the fractured – also depends on the conditions of loading, and the criteria of that fracture would be nonlocal. In consideration of the results of diagrams plotted from various bases for deformation measurement, a necessity of utilizing local material characteristics for calculation purposes is discussed. As an example of using the complete diagrams for determining kinetics of material degradation from external load, the results of specimen testing, which follows a cyclic training, are cited.
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Li, Fei-Fan, Gang Fang, and Ling-Yun Qian. "Forming limit analysis of Mg-2Zn-1.2Al-0.2Ca-0.2RE alloy sheet using ductile fracture models." International Journal of Damage Mechanics 29, no. 8 (2019): 1181–98. http://dx.doi.org/10.1177/1056789519855763.
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This work was aimed to experimentally and theoretically investigate the formability of a new magnesium alloy sheet at room temperature. The fracture forming limit diagram was predicted by MMC3 and DF2014 models, where the non-linear strain path effect was taken into account by means of damage accumulation law. In order to obtain the instantaneous values of the stress triaxiality and the Lode parameter during the deformation process, strains tracked by digital image correlation technique were transformed into stresses based on the constitutive equations. The fracture forming limit diagram predicted by the fracture models was compared with the forming limits obtained by ball punch deformation tests. The prediction errors were evaluated by the accumulative damage values, which verified the advantages of ductile fracture models in predicting the forming limits of the magnesium alloy sheets.
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Mohamed, M. Jinnah Sheik, and N. Selvakumar. "Studies on Formability Behaviour of Aluminium Alloy Sheets with Ceramic Nanocoatings." Advanced Materials Research 984-985 (July 2014): 482–87. http://dx.doi.org/10.4028/www.scientific.net/amr.984-985.482.
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Forming limit diagram presents limit strains for different linear strain paths. In other words it indicates localized formability of sheet metals under different proportional loading and is considered a powerful tool for trouble shooting in sheet-metal forming industries. In this study in-plane and out-of-plane forming limit diagrams were determined for aluminum 5052. In the experimental works, all specimens were prepared in the rolling direction and annealed before testing. Forming up to fracture was carried out on INSTRON UTM with a tensile force of 1N. The sheet samples were subjected to tension-compression state of strain by varying the notch sizes of the samples. FLD was drawn by plotting the minor strain in abscissa and corresponding major strain in ordinate and by drawing a curve which separates the safe region from the unsafe region.
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Park, Namsu, Hoon Huh, and Jeong Whan Yoon. "Anisotropic fracture forming limit diagram considering non-directionality of the equi-biaxial fracture strain." International Journal of Solids and Structures 151 (October 2018): 181–94. http://dx.doi.org/10.1016/j.ijsolstr.2018.01.009.
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8
Lyamina, Elena, Alexander Pirumov, and Yeong Maw Hwang. "An Approach for Predicting the Initiation of Ductile Fracture in Plane Strain Rolling." Key Engineering Materials 827 (December 2019): 379–84. http://dx.doi.org/10.4028/www.scientific.net/kem.827.379.
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The paper extends Orowan’s method to the prediction of ductile fracture in plane strain rolling. In general, any uncoupled ductile fracture criterion can be used in conjunction with the solution found. However, the present paper focuses on a ductile fracture criterion based on the workability diagram. It is assumed that the initiation of fracture occurs at the axis of symmetry.
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Qian, Z., Guang Ye, Erik Schlangen, and Klaas van Breugel. "3D Lattice Fracture Model: Application to Cement Paste at Microscale." Key Engineering Materials 452-453 (November 2010): 65–68. http://dx.doi.org/10.4028/www.scientific.net/kem.452-453.65.
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The fracture processes in cement paste at microscale are simulated by the 3D lattice fracture model based on the microstructure of hydrating cement paste. The uniaxial tensile test simulation is carried out to obtain the load-displacement diagram and microcracks propagation for a Portland cement paste specimen in the size of 100×100×100 µm3 at the degree of hydration 69%. The Young's modulus, tensile strength, strain at peak load and fracture energy are computed on the basis of the load-displacement diagram.
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Kovar, Martin, and Marek Foglar. "Design and Evaluation of the Method of Parameterization of the Force-Deflection Diagram of FRC." Advanced Materials Research 1106 (June 2015): 98–101. http://dx.doi.org/10.4028/www.scientific.net/amr.1106.98.
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Fiber-reinforced concrete (FRC) has mechanical properties that enhance its suitability for use in structures subjected to high strain rates, e.g. blast or impact loading. The fracture energy value is the decisive material characteristic for assessing the damage to concrete structures due to loadings with high strain rates. An analytical description of the force-deflection diagram of FRC can be a very efficient instrument for making a preliminary estimate of the fracture and mechanical properties of FRC. On the basis of our experiments and experiments from other authors, a tool for an analytical description of the force-deflection diagram for various strength classes, fiber types, etc. is proposed and evaluated.
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ZHAO, MIN, JIANGJUN ZHOU, ZHUANYI YU, et al. "A NEWLY DESIGNED ASSEMBLY LOCKING COMPRESSION PLATE TO TREAT COMMINUTED FRACTURES OF THE FEMORAL SHAFT: A BIOMECHANICAL STUDY." Journal of Mechanics in Medicine and Biology 19, no. 06 (2019): 1950059. http://dx.doi.org/10.1142/s0219519419500593.
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The aim of this paper is to compare the biomechanical characteristics of a newly designed assembly locking compression plate (NALCP) and traditional locking compression plate (LCP) for internal fixation of femoral-shaft comminuted fractures. A femoral-shaft wedge fracture model (AO classification 32-C2.1) was created in six pairs of femoral specimens ([Formula: see text]) randomly divided into two equal groups. Biomechanical properties were tested with axial and torsional loading tests. The relative maximum displacement of fracture blocks and strain was recorded. A strain diagram was made; the fatigue test results of NALCP specimens under axial load were recorded. Under axial load, the relative maximum displacement of fracture blocks in the [Formula: see text], [Formula: see text], and [Formula: see text] axes was smaller in NALCP specimens than in LCP specimens ([Formula: see text] and 0.01, respectively). Under torsional load, the relative maximum displacement of fracture blocks in the [Formula: see text] and [Formula: see text] axes in NALCP specimens was less than that in LCP specimens ([Formula: see text]) but no statistically significant difference in the [Formula: see text] axes ([Formula: see text]) was found. In both cases, the main NALCP strain was higher than the LCP strain ([Formula: see text]) but no statistically significant difference in mean strain ([Formula: see text]) was found. Our NALCP provides strong mechanical stability for comminuted femoral fractures and can effectively avoid stress concentration, reduce stress shielding, and facilitate bone healing.
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Venkatachalam, G., S. Narayanan, and Narayanan C. Sathiya. "Prediction of Limiting Strains for Square Pattern – Square Hole Perforated Commercial Pure Aluminium Sheets." Advanced Materials Research 548 (July 2012): 382–86. http://dx.doi.org/10.4028/www.scientific.net/amr.548.382.
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Forming limit diagram (FLD) is the most appropriate tool used to obtain the safe strain region in sheet metal forming industries. This FLD is based on limiting values of major and minor strains. This Limiting strain is the strain at the onset of fracture / necking in a sheet metal. It is influenced by the material / condition of the material, strain condition in geometrical features of a sheet metal. In this paper, square pattern – square holed, perforated commercial aluminium sheets are considered for the study. The limiting strain for the above perforated sheet metals is predicted using finite element analysis. It is found that the limiting strain is controlled by percentage of open area, ligament ratio and hole size.
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Rubešová, Kateřina, Martin Rund, Sylwia Rzepa, et al. "Determining Forming Limit Diagrams Using Sub-Sized Specimen Geometry and Comparing FLD Evaluation Methods." Metals 11, no. 3 (2021): 484. http://dx.doi.org/10.3390/met11030484.
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Sheet metal forming boundaries are established using the forming limit diagram (FLD). The Nakajima and Marciniak tests, which are based on stretching a material using a punch, are the most commonly used methods for determining the FLD or fracture forming limit diagram (FFLD). The results are usually evaluated by calculating local strain, strain rates, specimen thickness reduction or fracture strain. When the amount of experimental material is insufficient, miniaturization of the testing specimens may be a solution. However, the interchangeability of the results for standard and miniaturized specimens has not been proven yet. In this study, the Nakajima tests were performed using standard and sub-sized specimens made of manganese–boron steel 22MnB5, commonly used in the automotive industry. Afterwards, four FLD/FFLD evaluation methods were applied and compared. The miniaturized specimens yielded higher strain values, which was explained by the varied ratio of material thickness/punch diameter and different bending conditions. The highest compliance of the results was recorded for the standard and miniaturized FFLD.
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Kolesnikov, Gennadiy. "Analysis of Concrete Failure on the Descending Branch of the Load-Displacement Curve." Crystals 10, no. 10 (2020): 921. http://dx.doi.org/10.3390/cryst10100921.
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In this paper, load-displacement and stress-strain diagrams are considered for the uniaxial compression of concrete and under three-point bending. It is known that the destruction of such materials occurs on the descending branch of the load-displacement diagram. The attention of the presented research is focused on the explanation of this phenomenon. Fracture mechanics approaches are used as a research tool. The method for determining effective stresses and modulus of elasticity of concrete based on the results of uniaxial compression tests has been substantiated. The ratios necessary for the calculation were obtained without any assumptions about the reinforcement of concrete and the mechanical properties of its components. However, the effect of these properties is considered indirectly, using the stress and strain peaks determined by standard concrete compression tests. It was found that the effective stresses increase both on the ascending branch and on the descending branch of the load-displacement diagram. This explains the destruction of concrete on the descending branch of the load-displacement diagram. The results of determining the stresses and modulus of elasticity under uniaxial compression are comparable with the results obtained in experiments known in the literature.
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Kaputkina, Liudmila M., Vera Prokoshkina, and Yu I. Lojnikov. "Hot Strain Diagrams, Strengthening and Recrystallization of Nitrogen Alloyed Steels." Materials Science Forum 467-470 (October 2004): 281–86. http://dx.doi.org/10.4028/www.scientific.net/msf.467-470.281.
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Kinetics of deformation strengthening, polygonization and recrystallization processes have been studied, effects of alloying by nitrogen, combined carbon and nitrogen as well as by various other elements (Cr, Mo, Ni, Mn, V etc.) have been estimated for steels of different compositions and applications. Strain diagrams and structure state maps for the studied steels are presented. Strain diagram shape and attainable hot strength depend on the deformation conditions and basic alloying which determine strain hardening and diffusional processes of post-deformation softening. Alloying by nitrogen increases hot and cold strain hardening and retards recrystallization. Maximum strengthening obtained by cold deformation is accompanied by lowering of ductility and fracture toughness. Hence, it is applicable mainly to the austenitic steels. Nitrogen alloying enhances the austenite stability against g ® a transformation and consequently allows extending a composition range of steels which can be strengthened by cold deformation with large strains. The high-temperature thermomechanical treatment is more effective as a treatment improving a combination of mechanical properties. The schemes and regimes of thermomechanical strengthening treatments are proposed for low- and high- nitrogen containing steels of various structure classes.
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Zhou, Lin, and Xiao Min Cheng. "Prediction of T-Shaped Tube Hydroforming Stress Limit." Key Engineering Materials 480-481 (June 2011): 1140–43. http://dx.doi.org/10.4028/www.scientific.net/kem.480-481.1140.
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Tube hydroforming has been widely used in auto industry due to its remarkable advantages compared with conventional manufacturing via stamping and welding. The forming limit stress diagram (FLSD) which is independent of strain paths is of great significance to tube hydroforming. The FLSD of 2008T4 tube blank was established to predict fracture defect in T-shaped tube hydroforming simulation. By numerical simulation method, the stress limit and strain limit were analyzed and fracture defects were predicted. Two prediction results of the fracture defects location were the same yet the limit pressure values corresponding to fracture were different. The FLSD prediction result was close to the experiment result, so the accuracy of FLSD as tube hydroforming limit criterion was proved.
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Swaminathan, K., P. P. Date, and K. A. Padmanabhan. "Room Temperature Formability and Fracture Behavior of a High Strength AI-Zn-Mg Alloy." Journal of Engineering Materials and Technology 113, no. 2 (1991): 236–43. http://dx.doi.org/10.1115/1.2903398.
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The formability and fracture behavior of a high strength, aluminum alloy made to (French) specification AFNOR 7020 is reported. The formability study included the evaluation of the room temperature forming limit diagram (FLD) of the material in the T4 temper and an analysis of the strain distribution profiles obtained in punch stretching that involved different stress states. The fracture surfaces were examined by scanning electron microscopy and a correlation between the forming and fracture behavior could be obtained.
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Angella and Zanardi. "Validation of a New Quality Assessment Procedure for Ductile Irons Production Based on Strain Hardening Analysis." Metals 9, no. 8 (2019): 837. http://dx.doi.org/10.3390/met9080837.
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A mathematical procedure based on the analysis of tensile flow curves has been proposed to assess the microstructure quality of several ductile irons (DIs). The procedure consists of a first diagram for the assessment of the ideal microstructure of DIs, that is, the matrix where mobile dislocations move, and a second diagram for the assessment of the casting integrity because of potential metallurgical discontinuities and defects in DIs. Both diagrams are based on the dislocation-density-related constitutive Voce equation that is used for modeling the tensile plastic behavior of DIs. The procedure stands on the fundamental assumption that the strain hardening behavior of DIs is not affected by the nature and the density of the potential metallurgical discontinuities and defects, which are expected to affect only the elongations to fracture. However, this fundamental assumption is not obvious, and so its validity was evaluated through tensile testing Isothermed Ductile Irons (IDIs) 800, showing a wide scatter of elongations to rupture. The analysis of the strain hardening behaviors supported by strain energy density calculations of IDIs tensile tests proved that the fundamental assumption was valid and the quality assessment procedure could be applied to IDIs. A modified Voce equation was also introduced to improve the fitting of the experimental tensile flow curves and the strain energy density calculations.
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Situ, Q., Mukesh K. Jain, and M. Bruhis. "A Suitable Criterion for Precise Determination of Incipient Necking in Sheet Materials." Materials Science Forum 519-521 (July 2006): 111–16. http://dx.doi.org/10.4028/www.scientific.net/msf.519-521.111.
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Forming limit diagram (FLD) is a measure of the formability of a sheet material. The major-minor strain pairs that are closest to the neck on multiple specimens of various strain paths are utilized to construct a boundary between safe and unsafe zones. The challenge to obtain the FLD is the determination of incipient necking. Three approaches to determine the limit strains have been investigated and compared in this research in order to establish the optimal one for implementation: (1) commonly used Bragard criterion ( 1)e Br with periodic grids; (2) tracking the region of large local strains from strain history to locate the instance when critical major strain ( 1)e cr happens; (3) post-processing of strain history to locate the inflection in the major strain rate curve 1 max (e&&) at the onset of localization. The last criterion of inflection in strain rate 1 max (e&&) carries both a numerical and a physical meaning towards developing an understanding of flow localization, formability and fracture.
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Mourad, Abdel-Hamid I. "Effect of Stress State on Mode II Stable Crack Extension." Key Engineering Materials 297-300 (November 2005): 1604–10. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.1604.
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The effect of assumption of plane state of stress on the predictability of experimental results observed during the mode II stable crack growth (SCG) through 8 mm thick compact tension specimens (CTS) of a workhardening aluminum alloy (D16AT) has been studied. Experimental results include load-sliding displacement diagram, extent of SCG, crack front geometry and fracture surface fractographs. The experimental results show that the crack extends in its own plane, the fracture surface is flat, smooth and free of any shear lip. The crack front geometry, which is straight initially, remains mostly so throughout the SCG. Theoretical investigations have been done using an elastic-plastic finite element scheme and the COA/COD criterion as the criterion governing the growth. Finite element results, assuming plane stress and plane strain conditions separately, on the load-sliding displacement diagrams, J-resistance curve, plastic zones and variation of equivalent stress and strain along the crack-line ahead of the crack tip are also presented. The resistance curve is a straight-line and the magnitudes of equivalent stress and strain increases as the crack extension proceeds. In general, the predictions based on the assumption of plane state of stress are closer to the experimental results.
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Wang, Z. X., and R. Liu. "Elastic-Plastic Fracture Assessment for the Cracks Emanating from a Circular Hole under a Biaxial Loading Condition." Advanced Materials Research 602-604 (December 2012): 2241–44. http://dx.doi.org/10.4028/www.scientific.net/amr.602-604.2241.
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In this study, elastic-plastic stress and strain fields were analyzed on hole-edge cracks in an aluminum alloy plate under the biaxial load. And the effects of the load parallel to the crack face on failure parameters were discussed. By quantifying the effects of the crack size and the loading mode on the crack propagation driving force, J integral, and the plastic limit load, the corresponding failure assessment curves of the hole-edge cracked plate were established with the new R6 failure assessment diagram (FAD) method. The result shows that the transverse load has a larger effect on the failure assessment curve than crack length does, the safety zone of the failure assessment diagram gradually becomes smaller while transverse loading stress changes from tensile condition to compressed. Especially, when the transverse load acts as pressure, the Option 3 failure assessment diagram results to a smaller safety zone than the Option 1 failure assessment diagram does.
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Liu, Hong Wei, Sheng Jie Yao, Wen Liang Liu, and Zhao Duo Zhang. "Forming Limit Diagram of Magnesium Alloy ZK60 at Elevated Temperature." Advanced Materials Research 308-310 (August 2011): 2442–45. http://dx.doi.org/10.4028/www.scientific.net/amr.308-310.2442.
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The forming limit diagram of magnesium alloy ZK60 was developed with Hill’s instability criterion and M-K analysis. The relationship of forming limit with stain path, temperature and the thickness irregular coefficient were analyzed. The results show that the forming limit of ZK60 magnesium alloy increased little with the rising of strain ratio, but influenced greatly by the failure definition , and forming limit of is increased with the rising of temperature and thickness irregular coefficient, the most suitable value of f0 is 0.99, the fracture occur on the grain boundaries with significant cavities formation.
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SLAITAS, Justas, Zbynek HLAVAC, and Arnoldas ŠNEIDERIS. "FLEXURAL REINFORCED CONCRETE ELEMENTS NORMAL SECTION BEARING CAPACITY EVALUATION IN FRACTURE STAGE." Engineering Structures and Technologies 9, no. 2 (2017): 70–78. http://dx.doi.org/10.3846/2029882x.2017.1322919.
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This article examines flexural reinforced concrete structures condition assessment process in existing buildings on the stage where the reinforcement stress is between the yield and the tensile strength. The research is made on V. Jokūbaitis proposed methodology directly measuring the compression zone height, allowing us to evaluate the behavior of reinforced concrete beam fracture sufficiently precisely. This paper confirms the hypothesis that, when reinforcement reaches yielding stress, elastic strain dominates in concrete‘s compression zone and it is reasonable to use triangular concrete compression zone diagram, without tensile concrete above crack evaluation. The methodology of reinforced concrete structures bearing capacity assessment according to limit normal section crack depth is proposed. There is established connection between bending moments, when reinforcement achieve yielding stress and tensile strength, which allows us to decide about structures bearing capacity reserve. The results are confirmed with experimental studies and calculated values obtained by methodologies based on different reduced stress diagrams of concrete‘s compressive zone.
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Hirahara, Atsushi, Ryutaro Hino, and Fusahito Yoshida. "Forming Limit of Holed Dome in Two-Stage Stretch Forming." Advanced Materials Research 146-147 (October 2010): 844–47. http://dx.doi.org/10.4028/www.scientific.net/amr.146-147.844.
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This paper deals with the accurate prediction of forming limit of a dome with a circular hole in two-stage stretch forming. Since this two-stage forming is a process of non-proportional deformation, a fracture criterion, which is capable to predict fracture limit of sheet metal under non-proportional strain path, is introduced. The limit dome height of steel blank is predicted by utilizing numerical optimization technique, in which the fracture criterion is used as a constraint function to avoid sheet breakage. The calculated result and the corresponding experimental result show that the fracture criterion can successfully predict the limit dome height in the two-stage forming while the classical forming limit diagram (FLD) overestimates it.
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Alexandrov, S., M. Vilotic, Y. R. Jeng, and M. Plancak. "A Study on Material Workability by Upsetting of Non-Axisymmetric Specimens by Flat Dies." Journal of Mechanics 30, no. 6 (2014): 585–92. http://dx.doi.org/10.1017/jmech.2014.67.
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AbstractUpsetting is a typical test for determining the workability diagram. In most cases axisymmetric samples are used for such tests. However, the shape of samples may have a significant effect on the ductile fracture initiation. Therefore, a greater variety of sample geometry should lead to a more accurate shape of the workability diagram. A difficulty here is that a theoretical treatment of samples in which three-dimensional flow occurs is more difficult and time consuming as compared to axisymmetric samples under axisymmetric loading. This difficulty can be overcome in the case of the ductile fracture criterion based on the workability diagram and the average value of the triaxiality factor. In particular, if fracture occurs at free surfaces then it is sufficient to determine experimentally in-surface strains after several stages of the upsetting process, up to the initiation of ductile fracture. After that, the corresponding point of the workability diagram can be found by means of a simple analytical procedure and numerical integration. This approach is used in the present paper to correct the workability diagram using non-axisymmetric upsetting of five different samples made of steel. Some previous results are combined with the new results to obtain the workability diagram over a wide range of the triaxiality factor.
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Quan, Guo-zheng, Gui-chang Luo, An Mao, Jian-ting Liang, and Dong-sen Wu. "Evaluation of Varying Ductile Fracture Criteria for 42CrMo Steel by Compressions at Different Temperatures and Strain Rates." Scientific World Journal 2014 (2014): 1–10. http://dx.doi.org/10.1155/2014/579328.
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Fracturing by ductile damage occurs quite naturally in metal forming processes, and ductile fracture of strain-softening alloy, here 42CrMo steel, cannot be evaluated through simple procedures such as tension testing. Under these circumstances, it is very significant and economical to find a way to evaluate the ductile fracture criteria (DFC) and identify the relationships between damage evolution and deformation conditions. Under the guidance of the Cockcroft-Latham fracture criteria, an innovative approach involving hot compression tests, numerical simulations, and mathematic computations provides mutual support to evaluate ductile damage cumulating process and DFC diagram along with deformation conditions, which has not been expounded by Cockcroft and Latham. The results show that the maximum damage value appears in the region of upsetting drum, while the minimal value appears in the middle region. Furthermore, DFC of 42CrMo steel at temperature range of 1123~1348 K and strain rate of 0.01~10 s-1are not constant but change in a range of 0.160~0.226; thus, they have been defined as varying ductile fracture criteria (VDFC) and characterized by a function of temperature and strain rate. In bulk forming operations, VDFC help technicians to choose suitable process parameters and avoid the occurrence of fracture.
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Urbahs, Alexander, Mukharbiy Banov, Vladislav Turko, and Kristine Tsaryova. "The Characteristic Features of Composite Materials Specimen’s Static Fracture Investigated by the Acoustic Emission Method." Applied Mechanics and Materials 232 (November 2012): 28–32. http://dx.doi.org/10.4028/www.scientific.net/amm.232.28.
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The work is dedicated to the experimental study of micromechanics process of unidirectional composite materials’ specimens under static loading till its fracture using acoustic emission method compared with the strain-load deformation curve. An attempt is made to identify subtle effects of the failure process of the composite material which is impossible using the traditional methods of the strain measurement. The prospect of applying the method of acoustic emission (AE) for the development and improvement of existing methods of model tense- analysis is shown. The characteristic stages of the damage accumulation for unidirectional composites’ specimens and the effect of training on these processes are shown experimentally. It’s shown that the AE-deformation diagram have three stages in contrast to commonly used load-strain deformation curve with one stage. So it become possible to investigate the physical process of composite unit’s fracture under static load.
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Aranđelović, Mihajlo, Simon Sedmak, Radomir Jovičić, et al. "Numerical and Experimental Investigations of Fracture Behaviour of Welded Joints with Multiple Defects." Materials 14, no. 17 (2021): 4832. http://dx.doi.org/10.3390/ma14174832.
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Current standards related to welded joint defects (EN ISO 5817) only consider individual cases (i.e., single defect in a welded joint). The question remains about the behaviour of a welded joint in the simultaneous presence of several different types of defects, so-called multiple defects, which is the topic of this research. The main focus is on defects most commonly encountered in practice, such as linear misalignments, undercuts, incomplete root penetration, and excess weld metal. The welding procedure used in this case was metal active gas welding, a common technique when it comes to welding low-alloy low-carbon steels, including those used for pressure equipment. Different combinations of these defects were deliberately made in welded plates and tested in a standard way on a tensile machine, along with numerical simulations using the finite element method (FEM), based on real geometries. The goal was to predict the behaviour in terms of stress concentrations caused by geometry and affected by multiple defects and material heterogeneity. Numerical and experimental results were in good agreement, but only after some modifications of numerical models. The obtained stress values in the models ranged from noticeably lower than the yield stress of the used materials to slightly higher than it, suggesting that some defect combinations resulted in plastic strain, whereas other models remained in the elastic area. The stress–strain diagram obtained for the first group (misalignment, undercut, and excess root penetration) shows significantly less plasticity. Its yield stress is very close to its ultimate tensile strength, which in turn is noticeably lower compared with the other three groups. This suggests that welded joints with misalignment and incomplete root penetration are indeed the weakest of the four groups either due to the combination of the present defects or perhaps because of an additional unseen internal defect. From the other three diagrams, it can be concluded that the test specimens show very similar behaviour with nearly identical ultimate tensile strengths and considerable plasticity. The diagrams shows the most prominent yielding, with an easily distinguishable difference between the elastic and plastic regions. The diagrams are the most similar, having the same strain of around 9% and with a less obvious yield stress limit.
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Cao, Jun, Fuguo Li, Weifeng Ma, et al. "A Strain Rate Dependent Fracture Model of 7050 Aluminum Alloy." Metals 10, no. 1 (2019): 3. http://dx.doi.org/10.3390/met10010003.
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The purpose of this research is to predict fracture loci and fracture forming limit diagrams (FFLDs) considering strain rate for aluminum alloy 7050-T7451. A fracture model coupled Johnson-Cook plasticity model was proposed to investigate its strain rate effect. Furthermore, a hybrid experimental-numerical method was carried out to verify the strain rate-dependent fracture model by using fracture points of uniaxial tension, notched tension, flat-grooved tension, and pure shear specimens. The results show that the fracture points are in accordance with the fracture loci and FFLDs under different strain rates. The increasing strain rate decreases the FFLDs of aluminum alloy 7050-T7451. The difference of force-displacement responses under different strain rates is larger for notched tension and pure shear conditions.
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Safari, Mehdi, S. J. Hosseinipour, and H. D. Azodi. "An investigation into the effect of strain rate on forming limit diagram using ductile fracture criteria." Meccanica 47, no. 6 (2011): 1391–99. http://dx.doi.org/10.1007/s11012-011-9521-2.
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Ota, Tomoyuki, and Takashi Iizuka. "Fundamental Investigation for Tensile Test Using Conical Cupping Die." Key Engineering Materials 622-623 (September 2014): 292–99. http://dx.doi.org/10.4028/www.scientific.net/kem.622-623.292.
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A number of researches have conducted in order to evaluate the ductile fracture occurrence by using forming limit diagram. However, specimen shape and testing machine for obtaining forming limit diagram of sheet metal have some problems. The problem about specimen shape is occurring at the specimen edge. In uniaxial tensile test, the specimen edge may cause a defused neck in width direction and may have influence on fracture occurrence. In biaxial tensile test by using a cruciform specimen, a uniform biaxial deformation is not obtained because uniaxial tensile stress occurs at the specimen edge. Tensile test by using a specimen which does not have such edges should carry out, for example, in bulge test and multi-axial tube expansion test, specimens without edge are used. However, these methods need special machines. Therefore, new biaxial tensile testing method is required. By this method, materials deform depending on biaxial strain state by using popular pressing machines.
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Kvačkaj, Tibor, Juraj Tiža, Július Bacsó, et al. "Cockcroft-Latham Ductile Fracture Criteria for Non Ferrous Materials." Materials Science Forum 782 (April 2014): 373–78. http://dx.doi.org/10.4028/www.scientific.net/msf.782.373.
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The determination of ductile fracture criteria as well as friction coefficient, stress-strain curves, constants for Hollomon's equation and a material workability based on analytical methods as a forming limit diagram, a normalized Cockcroft-Latham criteria (nCL)) ring and compression tests for two materials based on aluminum and copper alloys were carried out. A calculation of nCL criteria on the basis of a compression test and numerical simulations was made. The critical values nCL criteria resulting from compression test were determined. Prediction of nCL criteria by numerical simulations were confirmed by laboratory compression tests. The values obtained from numerical simulations and compression tests for both materials show a good coincidence in results.
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Hojny, M., D. Woźniak, M. Głowacki, K. Żaba, M. Nowosielski, and M. Kwiatkowski. "Analysis Of Die Design For The Stamping Of A Bathtub." Archives of Metallurgy and Materials 60, no. 2 (2015): 661–66. http://dx.doi.org/10.1515/amm-2015-0189.
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Abstract The paper presents example results of numerical and photogrammetric analysis leading to identify the causes of cracking and wrinkling during bathtub W1200 production. The verification of tools for the stamping of bathtub W1200 was performed using finite element method and photogrammetric system ATOS Triple Scan. A series of industrial tests was conducted to identify the model parameters. The major and minor strain distributions obtained from the finite element simulations were used in conjunction with the forming limit diagram to predict the onset of fracture. In addition, the effects of blank holder pressure and friction on the occurrence of fracture and wrinkling were investigated.
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Takahashi, Sunao, Mutsumi Sano, Atsuo Watanabe, and Hideo Kitamura. "Prediction of fatigue life of high-heat-load components made of oxygen-free copper by comparing with Glidcop." Journal of Synchrotron Radiation 20, no. 1 (2012): 67–73. http://dx.doi.org/10.1107/s0909049512041192.
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Following a successful study on the prediction of fatigue life of high-heat-load components made of Glidcop, the thermal limitation of oxygen-free copper (OFC), which is used more commonly than Glidcop, has been studied. In addition to its general mechanical properties, the low-cycle-fatigue (LCF) and creep properties of OFC were investigated in detail and compared with those of Glidcop. The breaking mode of OFC, which was observed to be completely different from that of Glidcop in a fatigue fracture experiment, clarified the importance of considering the creep–fatigue interaction. An additional LCF test with compressive strain holding was conducted so that the creep–fatigue life diagram for out-of-phase thermal fatigue could be obtained on the basis of the strain-range partitioning method. The life predicted from elasto-plastic creep analysis agreed well with that determined from the void ratio estimated in the fatigue fracture experiment.
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Bondarev, B. A., N. N. Chernousov, and V. A. Sturova. "DETERMINATION OF DEFORMABILITY PARAMETERS OF CONCRETE SAMPLES BY THE FORMULAS OF FRACTURE MECHANICS." Construction and Geotechnics 11, no. 2 (2020): 88–98. http://dx.doi.org/10.15593/2224-9826/2020.2.08.
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To determine the deformability parameters of concrete samples by the formulas of fracture mechanics, equilibrium tests were carried out at the stage of local deformation of the sample, which showed the correspondence of the change in external forces to the internal forces of the material resistance with the corresponding static development of the main crack. For the same purpose, the samples are tested for bending with an initial notch and the “load-deflection” diagram is recorded. In this work, we presented a test scheme for a specimen with a notch (crack) and constructed a diagram of the deformation of a specimen under bending “load-deflection”. Based on it, it is possible to predict the destruction of the material, that is, to determine the value of the load at which the limit value of deflection or the displacement of the outer edges of the notch (opening the throat of the crack on the lower surface of the specimen) can be taken as the moment of loss of the resource of the material. Also, we examined the deformation of a concrete sample during three-point bending and presented a diagram of the deformation of a concrete sample within the plastic zone. Dependencies were derived for determining the ultimate relative strains under tension and bending. Based on the results obtained, the state diagrams of the stretched concrete and the deformation scheme of the normal section of the concrete sample were constructed. As a result, the conclusion and convergence of the results.
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Nizhnik, S. B., and E. A. Dmitrieva. "On the structural dependence of the stress–strain diagram parameters and fracture toughness of metastable austenitic steels." Strength of Materials 44, no. 3 (2012): 294–305. http://dx.doi.org/10.1007/s11223-012-9382-5.
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Liu, Bao Sheng, Wei Wu, and Xiu Quan Han. "Theoretical and Experimental Investigation on Forming Limit for TNW700 Titanium Alloy." Key Engineering Materials 622-623 (September 2014): 340–46. http://dx.doi.org/10.4028/www.scientific.net/kem.622-623.340.
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Forming limit is identified to evaluate the formability of sheet metal. The in-plane limit strains of sheets are plotted in a diagram with coordinates of major strain vs. minor strain. TNW700 titanium alloy is a high temperature resistant material. The products made of TNW700 can be used in a long serving period at 500°C, short time at 700°C. In this work, the forming limit of TNW700 will be investigated in theoretical and experimental ways. The experiment to test limit strains was carried out at 750°C under different loading paths. Marciniak – Kuczynski (M-K) model was calculated with Swift constitutive equations to predict the curves of limit strains. The effect of the groove angle on forming limit is that, the same angle on both sides of centerline determines the same FLC, and the limit points shift from left side to right side. The experiment shows that, the formability of TNW700 is not excellent, and it is lower than that of TC4 and TA15 at the same condition. The comparison shows that the curve predicted by M-K model is in a good agreement with that at plane strain, however higher than that in both sides. The fractographic observation shows that the fracture mode of TNW700 is dimple rupture.
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Habibi, Niloufar, Veera Sundararaghavan, Ulrich Prahl, and Ali Ramazani. "Experimental and Numerical Investigations into the Failure Mechanisms of TRIP700 Steel Sheets." Metals 8, no. 12 (2018): 1073. http://dx.doi.org/10.3390/met8121073.
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The formability and failure behavior of transformation-induced plasticity (TRIP) steel blanks were investigated through various stress states. The forming limit diagram (FLD) at fracture was constructed both experimentally and numerically. Numerical studies were performed to evaluate the applicability of different damage criteria in predicting the FLD as well as complex cross-die deep drawing process. The fracture surface and numerical results reveal that the material failed in a different mode for different strain path. Therefore, the Tresca model, which is based on shear stress, accurately predicted the conditions where shear had a profound effect on the damage initiation, whereas Situ localized necking criterion could calculate the conditions in which localization was dominant.
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Golestanian, Hossein, and Mahdieh Hamedi. "Fracture Analysis of Sinusoidal CNT-Based Nanocomposites with Uniform and Nonuniform CNT Distributions." Nano 10, no. 04 (2015): 1550058. http://dx.doi.org/10.1142/s1793292015500587.
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In this investigation, the effects of carbon nanotube (CNT) shape and distribution on nanocomposite failure are investigated. To achieve our goals, nanocomposites consisting of straight and sinusoidal CNTs with uniform and nonuniform distributions have been modeled. Failure of these nanocomposites is investigated using finite element simulations and micromechanics models. Initially, straight CNT-reinforced polymer is simulated and the stress–strain diagram for this nanocomposite is obtained. To validate our models, the simulation results of this nanocomposite are compared with those found in the literature. Then, sinusoidal CNT-reinforced polymers with uniform and nonuniform CNT distributions are modeled. The results are compared to determine the influence of CNT shape and distribution on nanocomposite failure mechanisms.
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Schmidt, Jaroslav, Alena Zemanová, Jan Zeman, and Michal Šejnoha. "Phase-Field Fracture Modelling of Thin Monolithic and Laminated Glass Plates under Quasi-Static Bending." Materials 13, no. 22 (2020): 5153. http://dx.doi.org/10.3390/ma13225153.
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A phase-field description of brittle fracture is employed in the reported four-point bending analyses of monolithic and laminated glass plates. Our aims are: (i) to compare different phase-field fracture formulations applied to thin glass plates, (ii) to assess the consequences of the dimensional reduction of the problem and mesh density and refinement, and (iii) to validate for quasi-static loading the time-/temperature-dependent material properties we derived recently for two commonly used polymer foils made of polyvinyl butyral or ethylene-vinyl acetate. As the nonlinear response prior to fracture, typical of the widely used Bourdin–Francfort–Marigo model, can lead to a significant overestimation of the response of thin plates under bending, the numerical study investigates two additional phase-field fracture models providing the linear elastic phase of the stress-strain diagram. The typical values of the critical fracture energy and tensile strength of glass lead to a phase-field length-scale parameter that is challenging to resolve in the numerical simulations. Therefore, we show how to determine the fracture energy concerning the applied dimensional reduction and the value of the length-scale parameter relative to the thickness of the plate. The comparison shows that the phase-field models provide very good agreement with the measured stresses and resistance of laminated glass, despite the fact that only one/two cracks are localised using the quasi-static analysis, whereas multiple cracks evolve during the experiment. It was also observed that the stiffness and resistance of the partially fractured laminated glass can be well approximated using a 2D plane-stress model with initially predefined cracks, which provides a better estimation than the one-glass-layer limit.
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Rizov, V., and A. Mladensky. "Fracture Toughness of Laminated Composites – A Non-Linear Analysis." Polymers and Polymer Composites 20, no. 8 (2012): 711–16. http://dx.doi.org/10.1177/096739111202000806.
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Non-linear fracture behaviour of laminated composite materials under mode I (crack opening) loading conditions was studied experimentally and theoretically. For this purpose, single edge notched tension (SENT) tests were carried-out using displacement-controlled loading under room temperature dry conditions. It was found that the load-displacement diagram had non-linear character prior to onset of macroscopic crack propagation. Thus, the main objective of this paper was to study the fracture properties using non-linear fracture mechanics. A two-dimensional finite element model was set-up in order to analyze the non-linear response of the SENT test specimen. Non-linear deformation due to damage was simulated using the Tsai-Hill failure criterion. The failure analysis revealed that the damage was localized in the vicinity of the crack tip. The fracture response was characterized using a J-integral. It was shown that a realistic appraisal of the potential for crack growth should include the effects of non-linear material deformation. It was found that taking into account the non-linear deformation increased the fracture resistance. This finding was attributed to the increased strain energy dissipation due to the damage induced non-linear behaviour of the SENT test specimen.
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Chi, Xiaolou, Ke Yang, and Zhen Wei. "Investigation of Energy and Damage Evolutions in Rock Specimens with Large-Scale Inclined Prefabricated Cracks by Uniaxial Compression Test and AE Monitoring." Advances in Civil Engineering 2020 (September 7, 2020): 1–12. http://dx.doi.org/10.1155/2020/8887543.
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To explore the energy dissipation mechanism and damage evolution characteristics of rock specimens under compressive loading, we performed the acoustic emission (AE) testing under uniaxial compression in intact rock specimens and those with large-scale prefabricated cracks. The basic mechanical properties of both types of specimens were analyzed comprehensively, and the evolution patterns of strain energy indicators (total strain, elastic, and dissipative energies) in rock specimens before the peak on the stress-strain curve were identified. We further revealed the effect of the prefabricated crack dip angle, which controlled the surplus energy conversion of the following peak deformation and failure in the rock specimens. Using the modified equation of rock specimen damage evolution characterized by the AE energy and examining the fracture surface morphology via the scanning electron microscopy (SEM), the AE distribution law for rock specimen damage was revealed. An increase in the prefabricated crack dip angle was shown to reduce the peak stress and strain of rock specimens, which experienced a transition from the tensile and splitting failure mode to shear and slip one. Cracked rock specimens exhibited strain energy accumulation at the elastic deformation stage of the stress-strain diagram and rapid energy consumption at the plastic stage. By contrast, the intact rock specimens had a smoother energy evolution pattern. As the prefabricated crack dip angle increased, the dissipated and surplus strain energies’ shares increased. Moreover, the first peak of the AE energy occurred earlier, and the stress needed for its occurrence decreased as the dip angle increased. According to the damage evolution equation for rock specimens, their damage process can be subdivided into the initial damage, stable damage increase, and the accelerating damage increase stages. An increase in the prefabricated crack dip angle accelerated the damage accumulation in rock specimens. The locking effect of the sawtooth-like structures on the fracture surface was less conspicuous, and the fracture surface roughness increased. Thus, microcracks gradually developed, and rock specimens became more susceptible to sudden unstable failure.
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Zubeil, Martin, Karl Roll, and Marion Merklein. "Extension of a Failure Criterion for Hemming Applications in the FEM Simulation." Key Engineering Materials 504-506 (February 2012): 765–70. http://dx.doi.org/10.4028/www.scientific.net/kem.504-506.765.
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In the FEM calculation of sheet metal forming processes to determine the failure case, the forming limit diagram is basically used. To determine the failure case at bending condition, the forming limit diagram can not be used. This behaviour was shown by many authors. Bending tests with an aluminium material (AC170PX) have shown that a high deformation ratio can be achieved without failure. Based on the loading conditions and the previous strain path through the deep-drawing process, a resulting bendability at a certain point can be obtained. Depending on the pre-damage and the mentioned loading conditions of the material failure will be occurring during bending at different times. Current developments of failure criteria consider the failure as in ductile fracture or shear fracture, which must be considered separately in the simulation. To rule out a separate analysis of the mode of failure in the post-processing, an existing failure criterion is extended and will be presented in this work. For the applications flanging and hemming the following extension of a stress-based failure criterion is proposed. Based on the triaxiality and the equivalent plastic strain a monitoring of the stress ratio is implemented in the FEM simulation. During the forming simulation the monitoring system observe the stress ratio based on the principal stresses resulted from the integration (Gauss) point of the shell element. According to the evaluation of the stress ratio evolution, a relevant definition will take into account how the damage will be accumulated. If the critical value of damage in the integration point of the shell element is reached, failure will be occur based on the position of the sheet thickness.
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Sarkar, Aritra, A. Nagesha, R. Sandhya, and M. D. Mathew. "Generation of Constant Life Diagram under Elevated Temperature Ratcheting of 316LN Stainless Steel." High Temperature Materials and Processes 35, no. 4 (2016): 361–68. http://dx.doi.org/10.1515/htmp-2014-0118.
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AbstractCombined influence of mean stress and stress amplitude on the cyclic life under elevated temperature (823–923 K) ratcheting of 316LN austenitic stainless steel is discussed. Constant life Haigh diagrams have been generated, using different combinations of stress amplitude and mean stress. In the plastic domain, the allowable stress was found to increase or decrease with mean stress depending on the temperature and combination of mean stress – stress amplitude employed. Strong influence of dynamic strain aging (DSA) was found at 823 K which affected the mode of deformation of the material in comparison with 923 K. Failure mode expressed through a fracture mechanism map was found to change from fatigue to necking depending on the test temperature as well as combinations of mean stress and stress amplitude. Occurrence of DSA at 823 K proved to be beneficial by way of extending the safe zone of operation to higherR-ratios in comparison with 923 K.
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Lapovok, Rimma, and Peter D. Hodgson. "Determination of Lower-Bound Ductility for AZ31 Magnesium Alloy by Use of the Bulge Specimens." Journal of Engineering Materials and Technology 129, no. 3 (2006): 407–13. http://dx.doi.org/10.1115/1.2744400.
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Despite the high demand for industrial applications of magnesium, the forming technology for wrought magnesium alloys is not fully developed due to the limited ductility and high sensitivity to the processing parameters. The processing window for magnesium alloys could be significantly widened if the lower-bound ductility (LBD) for a range of stresses, temperature, and strain rates was known. LBD is the critical strain at the moment of fracture as a function of stress state and temperature. Measurements of LBD are normally performed by testing in a hyperbaric chamber, which is highly specialized, complex, and rare equipment. In this paper an alternative approach to determine LBD is demonstrated using wrought magnesium alloy AZ31 as an example. A series of compression tests of bulge specimens combined with finite element simulation of the tests were performed. The LBD diagram was then deduced by backward calculation.
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Soomro, M. Waseem, M. Akhtar, R. Khan, and S. Altaf. "Experimental Investigation of Mechanical Properties and Forming Capabilities in Thin Magnesium Sheet at Elevated Temperature." Applied Mechanics and Materials 315 (April 2013): 527–30. http://dx.doi.org/10.4028/www.scientific.net/amm.315.527.
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This paper investigates the mechanical properties and forming capabilities of magnesium ZE10. Mechanical properties are observed by stress strain diagram. Three types of the samples are used which are machined from thin sheets of 0.8mm thickness in 00, 450, 900 of the rolling direction (RD). The samples are then tested at different temperatures varying from room temperature (RT) to 400°C. The factors that are considered in tensile tests are Youngs modulus, Yield strength, Ultimate tensile strength and fracture strain. The later part of this paper is devoted to deep drawing tests in which specimen are drawn from room temperature to 250°C. In these tests variation of Limit Drawing Ratio (LDR) is investigated at different temperatures. The other parameters observed are drawing depth, punch force, blank holder force and their variation from room temperature to elevated temperature.
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Sun, Lirong, Zhongyi Cai, Dongye He, and Li Li. "Aluminum Alloy Sheet-Forming Limit Curve Prediction Based on Original Measured Stress–Strain Data and Its Application in Stretch-Forming Process." Metals 9, no. 10 (2019): 1129. http://dx.doi.org/10.3390/met9101129.
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A new method, by directly utilizing original measured data (OMD) of the stress–strain relation in the Marciniak–Kuczynski (M–K) model, was proposed to predict the forming limit curve (FLC) of an aluminum alloy sheet. In the groove zone of the M–K model, by establishing the relations of the equivalent strain increment, the ratio of shear stress to the first principle stress and the ratio of the second principle stress to the first principle stress, the iterative formula was established and solved. The equations of theoretical forming limits were derived in detail by using the OMD of the stress–strain relation. The stretching specimens of aluminum alloy 6016-T4 were tested and the true stress–strain curve of the material was obtained. Based on the numerical simulations of punch-stretch tests, the optimized specimens’ shape and test scheme were determined, and the tests for FLC were carried out. The FLC predicted by the proposed method was more consistent with the experimental results of FLC by comparing the theoretical FLCs based on OMD of the stress–strain relation and of that based on traditional power function. In addition, the influences of anisotropic parameter and groove angle on FLCs were analyzed. Finally, the FLC calculated by the proposed method was applied to analyze sheet formability in the stretch-forming process, and the predicted results of FLC were verified by numerical simulations and experiments. The fracture tendency of the formed parts can be visualized in the forming limit diagram (FLD), which has certain guiding significance for fracture judgment in the sheet-forming process.
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Lee, C. F., and K. L. Lee. "EndoFEM Studies in the Mode I Stable Crack Growth of Fatigue Precracked CT Specimen." Journal of Mechanics 15, no. 4 (1999): 157–67. http://dx.doi.org/10.1017/s1727719100000447.
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AbstractIn this paper, the EndoFEM incorporated with a node duplicated and then unloaded crack extension methodology, is employed to produce the CT specimen of A1 2024-T3 with initial fatigue crack and then to simulate its stable crack growth under Mode I condition. Using the experimental P-LLD data, the P-Δa diagram can be estimated by the effective compliance method. This results in a further simulation of crack extending procedures which can obtain the stress-plastic strain distributions of growing crack front and their crack opening profiles, CTOD and CTOA vs. Δa Diagram, COD and COA measured at 5 positions behind the original crack tip vs. Δa diagram. The results mentioned above have excellent agreements with results of related experiments and other computational simulations.In consequence, the paper proposes a single fracture parameter of crack growth which can be casted in the future studies of EndoFEM simulation: (1) Within the crack initiation range whose crack extension rates da/dP has the lowest constant value, the COA measured at 0.5mm behind the original crack tip is takes as 5°; (2) Within the stable crack growth region whose crack extension rates are nonlinearly and monotonically increasing with finite values, the COA measured at 1mm behind the current crack tip is also taken as 5°.
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Chen, Y. Y., L. B. Chou, L. H. Wang, J. C. Oung, and H. C. Shih. "Electrochemical Polarization and Stress Corrosion Cracking of Alloy 690 in 5-M Chloride Solutions at 25°C." Corrosion 61, no. 1 (2005): 3–11. http://dx.doi.org/10.5006/1.3278159.
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Abstract An experimental, potential-pH diagram was constructed for the nickel-based Alloy 690 (UNS N06690) in 25°C concentrated (5 M) sodium chloride (NaCl) solution, using an electrochemical hysteresis method. The domains of immunity, general corrosion, passivation, and pitting in 5-M NaCl solutions were defined. At pH > 4, the passive region subdivided into areas of perfect passivation, imperfect passivation, and pitting. After anodic polarization, the surface of each specimen was carefully examined metallographically. Pitting corrosion was observed over the entire pH range investigated (0.3 to 8.52), but general corrosion predominated at lower pH values (<3). On the other hand, the mechanical properties, such as ultimate tensile strength (UTS), strain at fracture, and the reduction area (RA) measured by the slow strain rate test (SSRT), decreased significantly at pH < 3. The SSRT results are consistent with fractography and side-view observations of the tested specimens by scanning electron microscopy (SEM).
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Nikbin, K. M., D. J. Smith, and G. A. Webster. "An Engineering Approach to the Prediction of Creep Crack Growth." Journal of Engineering Materials and Technology 108, no. 2 (1986): 186–91. http://dx.doi.org/10.1115/1.3225859.
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This paper is concerned with assessing the integrity of cracked engineering components which operate at elevated temperatures. Fracture mechanics parameters are discussed for describing creep crack growth. A model is presented for expressing growth rate in terms of creep damage accumulation in a process zone ahead of the crack tip. Correlations are made with a broad range of materials exhibiting a wide spread of creep ductilities. It is found that individual propagation rates can be predicted with reasonable accuracy from a knowledge only of the material uni-axial creep ductility. An engineering creep crack growth assessment diagram is proposed which is independent of material properties but which is sensitive to the state of stress at the crack tip. Approximate bounds are presented for plane stress and plane strain situations and it is shown that crack growth rates about fifty times faster are expected under plane strain conditions than when plane stress prevails.