Plastic Work Research Articles

Influence of H2S Corrosion on Tensile Properties and Fracture Toughness of X80 Pipeline Steel

Tensile and fracture properties of X80 pipeline steel were studied in a mimic petrochemical environment. X80 pipeline steel specimens were firstly exposed to air or H2S corrosive medium. Then their tensile properties and δ-∆a resistance curves were obtained in experiments. The influence of H2S corrosion on the X80 pipeline steel’s crack growth resistance curve, fracture toughness, and plastic work loss was analyzed. The comparison between the test results after two pretreatments indicates that there was no significant difference in the X80 pipeline steel’s ultimate tensile strength before and after H2S corrosion. But fracture elongation, area reduction and fracture toughness varied greatly (a substantial decrease in elongation and reduction of area). The crack growth resistance curve of the specimen in air was obviously higher than the crack growth resistance curve of the corroded one. Under stable crack growth stage, the crack initiation toughness δ 0.2BL of the specimen in air was 0.732 mm, 2.02 times that of the corroded one (0.364 mm). In the case of similar crack growth ∆a, the plastic work required in the crack growing process (UP) of the specimen in air was 2.29 times that of the H2S-corroded specimen ( $$ {U}_P^{\hbox{'}} $$ ). H2S corrosion resulted in a significant reduction of the fracture toughness of X80 pipeline steel. Hence, H2S corrosion should be avoided in the process of natural gas transportation by pipelines, so as to protect the pipeline steel from toughness degradation.

Evaluation of the heat dissipated around the crack tip of AISI 422 and CF3M steels by means of thermography

The fatigue crack growth depends on the dissipated energy at the crack tip and in this regard, different analytical and numerical models were proposed by many researchers to describe as the plastic work affect the fatigue material behaviour. Experimental tests can be carried out for evaluating the energy dissipated during the crack growth principally based on the hysteresis loop measurement. However, these techniques need of suitable equipment and set-ups and then find some restrictions if applied in-situ and on real components.In this work, an experimental approach is used to obtain a thermographic parameter capable of describing the plastic work at the crack tip. The proposed approach is based on the phase shift of the thermal signal that occurs at the crack tip in the plastic area.Two specimens of two different steels, austenitic and martensitic, were tested and monitored with an infrared camera to collect thermoelastic phase data. A similar correlation to the dissipated energy was obtained with the fatigue crack growth behavior of materials.

Computational analysis of mesoscale thermomechanical ignition behavior of impacted LLM-105 based explosives.

LLM-105 (2,6-diamino-3,5-dinitropyrazine-1-oxide) is an insensitive high explosive crystal which has performance between that of HMX and TATB. An elastoviscoplastic dislocation model is developed for LLM-105 crystal, which accounts for the dislocation evolutions at the crystal interior and crystal wall and strain-rate dependent work hardening. Three different crystal morphology (cubic, icosahedral, rodlike) of LLM-105 based explosive computational models were constructed and subjected to an impact velocity of 200 m s−1 and 500 m s−1. Effects of crystal morphology and initial dislocation density on thermomechanical ignition behavior of LLM-105 based explosives were analyzed. Dislocation density of both crystal interiors and crystal walls in the rodlike LLM-105 based explosive increases slower than that in the cubic and icosahedral explosives. Both the volume averaged and localized stress and dislocation density are the lowest for the rodlike explosive. At the impact velocity of 500 m s−1, a temperature rise due to volumetric work, plasticity work and chemical reaction is sufficiently high to lead to the ignition of the cubic explosive, which shows that the rodlike explosive is the least sensitive among the three explosives. Moreover, with the increase of initial dislocation density, the corresponding volume averaged and localized stress and temperature increase as well. Results presented bridge the macroscale thermomechanical ignition response with the mesoscale deformation mechanisms, which is essential for better understanding the ignition mechanisms and guiding the design of LLM-105 based formulations.

Numerical investigation of the evolution of microstructure of nickel-based alloys during plastic working

The paper considers the process of hot plastic working of a large metal billet, which causes its upsetting to a dimension specified by the manufacturing technique and the average axial deformation of 32.5%. The billet was made of heat-resistant nickel alloy Waspalloy widely used in the aircraft industry. The structural condition of the deformed alloy and, consequently, its mechanical properties depend on many factors: the degree of deformation, the rate of deformation, recrystallization in the process of deformation. This generates a need for a comprehensive study of the plastic flow in the examined material and the influence of the deformation parameters on its characteristics. The paper presents the results of a numerical investigation of the deformation and temperature states of the billet that allowed us to analyze changes occurring in the structure of nickel alloy during plastic deformation at different upsetting rates (50 and 100 mm/s). The shape of billet lateral surface and the forces required to complete the process of free upsetting are calculated as well. The numerical simulation was performed by the finite element method using the DEFORM-2D/3D software package. The average grain size and the fraction of recrystallized grains in the body of the billet were determined based on the Johnson-Mehl-Avrami-Kolmogorov model (JMAK). The results of numerical modeling showed that the greatest change in the microstructure of the alloy occurs in the region of intense plastic strains. The upsetting rate of 100 mm/s leads to the formation of structure with finer grains compared to the structure formed at the upsetting rate of 50 mm/s.

Energy absorption of aluminum panels subjected to gelatin projectile impact

Abstract Digital image correlation (DIC) method has been widely used on dynamical experiments. This full-field and real-time method can fill in the gap of traditional point-based measurements of typical structures subjected to soft body impact such as bird strike. In order to get further understandings of soft body impact process, the present study analyzed the time-dependent energy exchange during impact experiments. The dynamic responses of the aluminum target panels were obtained using 3D digital image correlation method so that their displacement and strain field histories can be tracked. By introducing the material properties of the targets, their time-dependent stress state and consequently the strain energy can be calculated. With the help of time-dependent profiles of target panels, their energy absorption properties were theoretically analyzed, including the exchange of kinetic energy and plastic work. The results showed that when the impact loadings were increased, the plastic work generated by radial membrane force became the major source of energy dissipation. The transverse movements consumed more kinetic energies than rotatory moments. This research may provide a further application of DIC results and help to better understand the soft body impact process on targets with large deformations.

Numerical simulation of high-speed joining of sheet metal structures

Abstract The increasing trend of multi-material and space-frame design in automotive car body constructions consolidates the need for mechanical joining technologies with one-sided accessibility. The high-speed joining process (also called “RIVTAC®” or “Impact”) is an innovative and flexible technology. In this process, a tack having a profiled shank and an ogival shaped tip is pushed into the joining partners with a speed of 20 to 40 m/s without any pre-punching. The plastic and friction work is converted into heat, which causes an abrupt rise of temperature in the joining zone. This improves the flowability of the material which leads to filling the annular grooves existing on the shank of the tack. Simultaneously, a force-fit is created between the sheet metal and the tack. Furthermore, the effects of inertia are used so that the thin-walled structures can be joined without any additional tools (e.g. a die). The joining process causes the deformation of the structure, which must be taken into account with regard to tolerances. The numerical simulation is a powerful tool to predict the deformation and the joinability of a complex structure as well as the mechanical properties of the connection. The paper is about the detailed process- and load-simulation of high-speed joining as well as the required experimental data basis, such as temperature and strain rate dependent flow curves. Furthermore, the friction parameters are very important for the physical consideration of the force-fit connection. Coupled structural-thermal simulations of an axisymmetric 2D-model are performed using explicit and implicit codes.

The Loading Curve of Spherical Indentions Is Not a Parabola and Flat Punch Is Linear

The purpose of this paper is the physical deduction of the loading curves for spherical and flat punch indentations, in particular as the parabola assumption for not self-similar spherical impressions appears impossible. These deductions avoid the still common first energy law violations of ISO 14577 by consideration of the work done by elastic and plastic pressure work. The hitherto generally accepted “parabolas” exponents on the depth h (“2 for cone, 3/2 for spheres, and 1 for flat punches”) are still the unchanged basis of ISO 14577 standards that also enforce the up to 3 + 8 free iteration parameters for ISO hardness and ISO elastic indentation modulus. Almost all of these common practices are now challenged by physical mathematical proof of exponent 3/2 for cones by removing the misconceptions with indentation against a projected surface (contact) area with violation of the first energy law, because the elastic and inelastic pressure work cannot be obtained from nothing. Physically correct is the impression of a volume that is coupled with pressure formation that creates elastic deformation and numerous types of plastic deformations. It follows the exponent 3/2 only for the cones/pyramids/wedges loading parabola. It appears impossible that the geometrically not self-similar sphere loading curve is an h3/2 parabola. Hertz did only deduce the touching of the sphere and Sneddon did not get a parabola for the sphere. The radius over depth ratio is not constant with the sphere. The apparently good correlation of such parabola plots at large R/h ratios and low h-values does not withstand against the deduced physical equation for the spherical indentation loading curve. Such plots are unphysical for the sphere and so tried regression results indicate data-treatments. The closed physical deduction result consists of the exponential factor h3/2 and a dimensionless correction factor that is depth dependent. The non-parabola against force plot using published data is concavely bent even for large radius/depth-ratios at the shallow indents. The capabilities of conical/pyramidal/wedged indentations are thus lost. These facts are outlined for experimental nano- and micro-indentations. Spherical indentations reveal that linear data regression is suspicious and worthless if it does not correspond with physical reality. This stresses the necessity of the straightforward deductions of the correct relations on the basis of iteration-less and fitting-less undeniable calculation rules on an undeniable basic physical understanding. The straightforward physical deduction of the flat punch indentation is therefore also presented, together with formulas for the physical indentation hardness, indentation work, and applied work for these geometrically self-similar indentations. It is exemplified with a macroindentation.

Parameter-free shape optimization for minimizing plastic work of 3D rigid-plastic solids

Parameter-free shape optimization for minimizing plastic work of 3D rigid-plastic solids

Application of Ultrasonic Vibration to Manufacturing and Aspect of Application to Plastic Work

Application of Ultrasonic Vibration to Manufacturing and Aspect of Application to Plastic Work

The influence of process parameters and sheet material on the temperature development in the forming zone

Cold metal forming is a fast and economical way of producing a wide range of precise components. Its profitability mainly depends on part quality, process stability, and service intervals of tools. As these factors are all determined by tool wear, detailed process knowledge is indispensable to maximize profitability by minimizing wear. One of the most crucial factors in this context is temperature. During every forming process, a temperature rise occurs between tool and workpiece due to frictional heating and a large part of plastic work dissipating into heat. This phenomenon affects the whole forming process but especially tool wear. Currently, there is little solid information about temperatures occurring during forming operations. Therefore, the temperature was measured based on varying process parameters, sheet materials, and thicknesses in several embossing and blanking examinations. The use of a tool–workpiece thermocouple enabled accurate and instantaneous measurement during the process. The results presented show the strong influence of process and material parameters on temperatures in the forming zone.

A three-dimensional elastoplastic analysis of mixed-mode KI/KII around the crack front

Engineering problems that involve fatigue crack growth and fracture frequently can be studied by taking into account only mode-I features. However, many important problems that involve combined mode I and II loadings cannot be properly analyzed by a pure mode-I approach, which in particular may not be sufficient to estimate fracture toughness for practical purposes in such cases. Such mixed-mode problems involve crack orientation and/or load conditions that lead to combined local Stress Intensity Factors (SIFs) KI/KII around the crack front. Using multiaxial crack tip condition characterized by the crack inclination angle βin a mixed-mode KI/KII modified single edge tension SE(T) specimen, such mixed-mode effects on plastic zone shapes, volumes and plastic work UPL are taken into account to evaluate problems that involve fatigue and fracture.

Approach for modelling the Taylor-Quinney coefficient of high strength steels

Abstract Precise knowledge of the temperature that arises in the material during plastic forming is of crucial importance, as it has a significant influence on material behaviour and therefore on the forming process. In order to describe the amount of heat that is generated during plastic forming accurately, the Taylor-Quinney coefficient β was introduced as the ratio of dissipated heat to plastic work and generally assumed to be a constant value. However, recent studies have shown that there is a dependency on material and process-specific parameters. In this study, the Taylor-Quinney coefficient β is shown as a function of strain and being influenced by the test specific strain rate and stress state. The tested material is a dual-phase steel HCT980X. The uniaxial tensile test and the Marciniak test with different tallied specimen at forming-relevant global strain rates were investigated. By means of thermographic and optical measuring systems the temperature and local strains were recorded during the tests. Based on an approach similar to the finite volume method, both experimental setups were modelled taking heat transfer effects into account. As a result, the Taylor-Quinney coefficient is calculated by means of experimental data. It is shown that the Taylor-Quinney coefficient is a variable value depending on the flow behaviour of the steel. The local strain rate and the specimen geometries of Marciniak test have a significant influence on the arising heat conduction. The stress state, however, has minor influence on β.

Analysis of Anisotropic Plastic Properties of Perforated Sheet Metal Using Homogenization Method

In this study, the anisotropic plastic properties of perforated sheet metal with regular staggered holes were analyzed by the homogenization method. A hexagonal unit cell with periodic boundary conditions was selected for the analysis. To validate the analysis results, comparisons were made with the experimental results obtained from a uniaxial tensile test. The analyzed stress-strain curves obtained from directional tensile tests match the corresponding experimental stress-strain curves. The in-plane variations of the analyzed r-values also agree qualitatively with the experimental results. In the biaxial tensile test, the macro yield surface was evaluated as an equal plastic work contour in the proportional stress path. Obtained results indicate differential (anisotropic) hardening and slight tension-compression asymmetry of the subsequent macro yield surface. In the case of the proportional loading path, the associated flow rule (AFR) for the initial and subsequent yield surfaces is applicable. However, regarding the non-proportional loading path, the AFR may not be applicable in certain cases because the distribution patterns of the strain rate around the holes depend on the history of local work hardening.

Size-dependent plastic buckling behavior of micro-beam structures by using conventional mechanism-based strain gradient plasticity

Since the actuators with small- scale structures may be exposed to external reciprocal actions lead to create undesirable loads causing instability, the buckling behaviors of them are interested to make reliable or accurate actions. Therefore, the purpose of this paper is to analyze plastic buckling behavior of the micro beam structures by adopting a Conventional Mechanism-based Strain Gradient plasticity (CMSG) theory. The effect of length scale on critical force is considered for three types of boundary conditions, i.e. the simply supported, cantilever and clamped - simply supported micro beams. For each case, the stability equations of the buckling are calculated to obtain related critical forces. The constitutive equation involves work hardening phenomenon through defining an index of multiple plastic hardening exponent. In addition, the Euler-Bernoulli hypothesis is used for kinematic of deflection. Corresponding to each length scale and index of the plastic work hardening, the critical forces are determined to compare them together.

Numerical Verification of Simplified Identification Method of Yield Function Using Circumscribing Polygon of Yield Locus

A method for identifying the yield function using simple material tests is proposed. The identification accuracy of this method is verified by finite element analysis. In the proposed method, a polygon circumscribing the equal plastic work contour is defined through uniaxial tensile tests, hydraulic bulge test, and plane strain tensile tests. The parameters of the anisotropic yield function are identified as a smooth curve inscribed in the polygon. The virtual material tests of three material models, namely, mild steel, aluminium alloy, and pure titanium, are conducted by the finite element method. On the basis of the results, stress measurement error and yield surface identification error are discussed. When the material exhibits strong in-plane anisotropy, the measurement error of equi-biaxial stress in the hydraulic bulge test becomes large. When the initial gradient of work hardening is large, the stress value of the circumscribed line of the small plastic strain stage in the plane strain tensile test is estimated to be lower than that on the true yield surface. These errors affect the identification accuracy of the material parameters of the yield function quantitatively, but the difference between the identified locus and true yield locus is small. The proposed method is feasible as a simple identification method of the yield function.

Sinestesias en la notación gráfica: lenguajes visuales para la representación del sonido

Para representar los distintos fenómenos sonoros, la notación gráfica —escritura musical originada a mediados del pasado siglo— hace uso de una gran variedad de elementos del lenguaje visual. En este tipo de notación, la partitura actúa no solo como registro y motor de la experimentación musical llevada a cabo por los compositores de vanguardia, sino también como territorio de ensayos y pruebas con los diferentes lenguajes visuales. Este artículo profundiza en el conocimiento de los distintos lenguajes visuales utilizados en la notación gráfica con el fin de comprender cómo se relaciona el concepto musical de cada obra y compositor con el lenguaje visual elegido para su representación gráfica. Así, se ha llevado a cabo un estudio interdisciplinar de determinadas obras representativas de la notación gráfica realizada desde mediados del siglo XX hasta nuestros días, seleccionando los lenguajes visuales del cómic, el collage, la escultura, el vídeo y la película, la fotografía y el dibujo. Esta pone de manifiesto la naturaleza sinestésica de la notación gráfica y destaca el carácter creativo de esta forma de escritura musical, generadora de nuevos procesos sonoros y artísticos, así como de sugerencias y recursos interpretativos. Se enfoca en el estudio de la notación gráfica como fenómeno sinestésico, musical y plástico, tomando como punto de partida el lenguaje visual propio de cada partitura para comprender cómo dialogan imagen y sonido en cada caso, cómo el pensamiento musical se materializa en una obra que es también plástica, y viceversa, cómo una obra plástica genera nuevos procesos sonoros.

Numerical Analysis of Temperature Rise during Dynamic Loading for Dissimilar Steel Joint Specimen

In this study, dynamic temperature field in a dissimilar steel joint specimen was numerically analyzed by means of three-dimensional explicit finite element analysis. Fully coupled thermal stress analysis was performed by using FE-code Abaqus/Explicit ver. 6.12. It was assumed that 90% of the plastic work was transferred to heat. Furthermore, dynamic loading tests were conducted with three-point bending specimen extracted from the dissimilar steel joint between a mild steel and a high tensile strength class steel. The specimen included a U-shape notch in the bonded interface. A high-speed infrared camera was used to measure the temperature field near the bonded interface. The temperature field was recorded at a frame rate of 200 Hz during the dynamic loading test. The numerically calculated temperature field near bonded interface showed reasonable agreement with the temperature field measured by the high-speed infrared thermography. The temperature in the soft steel particularly increased during the dynamic loading. On the other hand, the increase in temperature in the hard steel area was relatively few.

Pintura e escultura como modelos para o coro no Livro II das Leis de Platão

Este artigo constitui-se de um comentário acerca do papel das artes na educação da segunda melhor cidade possível de Platão imaginada no último diálogo que escreveu, As Leis. A educação será realizada através do coro que, segundo nossa interpretação, seguirá os desenhos apresentados pelas pinturas e esculturas. Estas, como defenderemos, imitam diretamente a Ideia do Belo e talvez correspondam à imagem dos homens ideais da cidade da República. A educação vai do corpo, que dança e canta a partir de padrões expostos pelas obras plásticas, à alma. A arte mimética se faz essencial, portanto, na educação e, como explicitaremos, também na percepção do belo através de uma representação reta dos seres.

The stress’s state analysis of carbon fibre reinforced concrete elements evaluating the bond influence

While strengthening structures with thin layered elements an important role is carried out by the bond between separate elements, but there are not any methods which would describe the distribution of shear stress in the contact zone when the concrete works plastically. In this article a single span reinforced concrete beam which is strengthened by CFRP (Carbon fiber reinforced polymer) is analysed and three methods which could describe shear stress through the length of the element are provided. The three compared methods are: finite elements method (FEM), theory of multiple rods and the proposed method of the authors. The results are provided as diagrams and the similarities and differences are discussed. The method that the authors propose is superior to other methods because it describes the plastic work of a concrete which is not possible to evaluate with the method of the multiple rods theory DOI: http://dx.doi.org/10.5755/j01.sace.23.2.20987

Development of a Novel Cr21 Lean Duplex Stainless Steel and Its Hot Deformation Behavior

In this study, a novel Cr21 lean duplex stainless steel has been developed. In order to investigate the difference in hot workability between the novel steel and the conventional LDX2101, the hot deformation tests were carried out in the temperature ranges from 950 to 1150 °C and strain rate ranges from 0.01 to 10 s−1 by using a thermo-mechanical simulator. The peak stress increased with an increase in strain rate and a decrease in deformation temperature. However, the peak stress of the novel Cr21 lean DSS was always higher than that of the conventional LDX2101 under the same deformation conditions. The novel steel with lower deformation activation energy can be more easily deformed than the LDX2101. Meanwhile, the processing maps based on the specific plastic work approach indicated that the novel steel possessed a narrower flow instability region than the LDX2101. The lower difference in softening rate between ferrite and austenite can lead to the better deformation coordination in the novel steel compared to the LDX2101. The excellent hot workability of the novel steel can be obtained due to the low strength difference between the dual phases and the inhibition of the thin lamellar structures along the rolling direction on the transverse propagation of small cracks originating from the edge of the hot-rolled plates.