Free Deformation Research Articles

The evolution of LPSO phase and its influence on grain size during cooling free forging

In this paper, the deformation behavior of the LPSO phase of Mg-Gd-Y-Zn-Zr and its influence on the grain size are studied during the cooling free forging deformation. Studies have shown that cooling free forging can refine different forms of LPSO phases. The lamellar and block LPSO phases are kinked and broken during the deformation process. The kink angle and the number of kinks of the lamellar phase are greater than that of the block phase. With the increase of the cooling pass, the fragmentation of the lamellar phase is more violent. The kink and broken of the LPSO phase significantly refined the grain size by dividing the grains and promoting dynamic recrystallization. The grain size has dropped significantly from 113 μm in one pass to 12 μm in three passes. Uniform fine structure improves alloy mechanical properties through the Hall-Petch principle. The ultimate tensile strength of three-pass alloy reaches 323.2 MPa, the yield strength reaches 239.9 MPa, and the elongation reaches 17.1%.

Design and Analysis of Cam Wave Generator Based on Free Deformation in Non-Working Area of the Flexspline

Deformation stress of a flexspline under the action of a wave generator directly affects the service life of the flexspline and meshing quality of meshing pair. This study proposed a new deformation model for a flexspline, which incorporates forced deformation in the working area and free deformation in the non-working area, keeping the deformation shape unchanged during rotating. Based on this assumption of a deformation model, the mathematical model is further established, and the design approach of a cam wave generator is developed with the deflection curve of the ring structure. Then, a sample design with a double eccentric arc cam wave generator based on this deformation model is developed and analyzed in FEM. The results show that the deformation stress of the flexspline can be improved by relaxing the forced deformation in the non-working area, and the selected deformation shape can also remain unchanged during rotating. Moreover, the stress distribution and the maximum stress value could be improved with the variation of the combination coefficient, especially for the wrap angle.

STUDY ON ELASTIC PROPERTY OF STAINLESS STEEL UNDER PRESSURE

The paper presents analytic expressions of the Helmholtz free energy and characteristic elastic deformation quantities such as the elastic moduli E, K, G and the elastic constants C11, C12, C44 for BCC interstitial and substitutional alloy with four components are determined by the statistical moment method. The obtained elastic quantities depend on temperature, pressure, the concentration of interstitial atoms, and the concentration of substitutional atoms. This is the elastic deformation theory of BCC interstitial and substitutional alloy with four components published for the first time. The elastic deformation theories of BCC metal, BCC binary interstitial alloy, BCC binary substitutional alloy, and BCC ternary interstitial and substitutional alloy are limit cases of the elastic deformation theory of BCC substitutional and interstitial alloy with four components. Our numerical calculations of the obtained theoretical results for metal Fe and alloy FeSi are in good agreement with other calculations and experiments. Other numerical calculations for alloys FeCr, FeNi, FeCrSi, FeNiSi, FeCrNiSi (some atoms Fe are substituted by atoms Cr and some other atoms Fe are substituted by atoms Ni) called stainless steels predict and orient experimental results in the future. Our numerical calculations for alloy FeCrNiSi are published for the first time.

Tensile response of Ultra High Performance PE Fiber Reinforced Concretes (PE-UHPFRC) under imposed shrinkage deformations

PE-UHPFRC is a new Ultra High-Performance Fiber Reinforced Concrete (UHPFRC), which is developed to reduce the environmental impact of conventional UHPFRC by replacing the steel fibers with synthetic ones and reducing the clinker content in the mix. The development of the dynamic elastic modulus, the evolution of free autogenous deformations and the eigenstresses development with age, under full and partial restraint conditions, were investigated for PE-UHPFRC and the results were put into perspective with that for conventional UHPFRC with steel fibers. Furthermore, the tensile responses of different mixes under imposed shrinkage were compared and discussed. The results showed a shorter setting time and consequently an earlier initiation of elastic modulus development for PE-UHPFRC compared with that of conventional UHPFRC. Furthermore, the developed eigenstresses under full restraint conditions in a PE-UHPFRC layer compared with that for conventional UHPFRC were reduced by more than 70%, which is highly beneficial especially for cast-in-place rehabilitation applications.

Settlement and bearing capacity of water-saturated soils of foundations of finite width under static impact

Introduction. In case of brief exposure to static loads or dynamic loads, in conditions of absence of drainage, distribution of total stresses between the skeleton of soil and pore gas-containing water should be taken in account. The situation of the stress-strain state of the base is further complicated when we consider the degree of water-saturation of soil of the foundation (0.8 < Sr ≤ 1). The aim of the study is to pose and solve problem of the stress-strain state of a water-saturated soil massif, Including settlement and bearing capacity of a water-saturated base of a foundation of finite width, depending on the degree of water saturation of soils, taking into account the linear and nonlinear properties of the skeleton of soil and the compressibility of pore gas-containing water.
 Materials and methods. Henckyʼs system of physical equations are used as a calculation model to describe the relationship between deformation and stresses of soil, which takes into account the influence of the average stress on the deformation and strength properties of the soil. This system allows us to represent the linear deformation of the soil as the sum of the volumetric and shear components of the soil of this deformation. In addition allows us too to determine the deformation of the layer of soil, as part of the compressible thickness of the base of foundation with finite width under conditions of free deformations.
 Results. Depending on the linear and nonlinear deformation parameters, the settlement can be developed with a damped curve (S – p) and stabilize, and can be developed with a non-damped curve (S – p) and moved to the stage of progressive settlement.
 Conclusions. Solutions have been made for cases when the water-saturation of the base soils changes in the range of 0.8 to 1.0. It is shown that the settlement and bearing capacity of a water-saturated base significantly depends on the degree of water saturation of soils.

Strain Induced Surface Change in Sheet Metal Forming: Numerical Prediction, Influence on Friction and Tool Wear

In sheet metal forming, free deformation of the sheet takes place frequently without contact with forming tools. The pre-straining resulting from the free deformation leads to a surface roughening of the sheet metal. It is assumed that the roughening has an influence on friction and wear behavior of the following forming process as well as the painting quality after the manufacturing. In this paper, a numerical prediction based on a polycrystalline model is first proposed to predict the effect of surface roughing based on the material data of the as-received state of the sheet metal. Different states of strain are analyzed and the numerical result is validated through experimental evaluation. Besides the numerical prediction, the friction behavior after pre-straining is evaluated in strip drawing tests and the coefficient of friction (COF) is calculated. For interpretation of the measured COF, the surface roughness after the friction test and the surface image are evaluated by a transparent toolset. It is shown that the surface transformation as a result of pre-straining has a negative influence on the lubricating effect of the sheet metal and degrades the friction behavior. Finally, the influence of the strain-induced surface roughening on wear is discussed based on wear testing in strip drawing test with draw bead geometry.

Characterization of the vibration, stability and static responses of graphene-reinforced sandwich plates under mechanical and thermal loadings using the refined shear deformation plate theory

An analytical investigation was carried out to assess the free vibration, buckling and deformation responses of simply-supported sandwich plates. The plates constructed with graphene-reinforced polymer composite (GRPC) face sheets and are subjected to mechanical and thermal loadings while being simply-supported or resting on different types of elastic foundation. The temperature-dependent material properties of the face sheets are estimated by employing the modified Halpin-Tsai micromechanical model. The governing differential equations of the system are established based on the refined shear deformation plate theory and solved analytically using the Navier method. The validation of the formulation is carried out through comparisons of the calculated natural frequencies, thermal buckling capacities and maximum deflections of the sandwich plates with those evaluated by the available solutions in the literature. Numerical case studies are considered to examine the influences of the core to face sheet thickness ratio, temperature variation, Winkler- and Pasternak-types foundation, as well as the volume fraction of graphene on the response of the plates. It will be explicitly demonstrated that the vibration, stability and deflection responses of the sandwich plates become significantly affected by the aforementioned parameters.

Electron Backscatter Diffraction Investigation of Heat Deformation Behavior of 2205 Duplex Stainless Steel

Herein, the thermal compression of 2205 duplex stainless steel is simulated using a thermal simulation testing machine at 850–1100 °/0.01 s−1 and 850–1100 °/10 s−1, and the large deformation zone (LDZ) and free deformation zone (FDZ) of the structure are characterized by electron backscatter diffraction (EBSD). The study results show that the stress–strain curve with a strain rate of 10 s−1 hardens continuously. In addition, ferrite undergoes deformation mostly when the strain is less than 0.33, and strain hardening occurs in austenite after the strain reaches 0.33. As a result, the curve ascends and steepens, and secondary hardening occurs. Continuous dynamic recrystallization (CDRX) is distinctly observed in original ferrite grains, whereas the austenite grains are recrystallized discontinuously due to the bulging high‐angle grain boundaries (HAGBs). Meanwhile, the recrystallization fraction in the large deformation region of both ferrite and austenite is significantly higher than that in the free deformation zone. The orientation distribution function (ODF) diagram analysis reveals that ferrite is mainly composed of the rotation cube {001}<111> texture, and austenite mainly consists of the rolled α‐fiber texture, including brass {011}<211>, Gauss {011}<100>, and {011}<111>.

Regulation of thermoelastic properties of concave-packaged DNA adsorption films and its relevant microcantilever detection signals

The packing patterns have close correlation with the thermoelastic properties of DNA adsorption films and the relevant detection signals of microcantilevers. In this paper, we investigate the influence of packing patterns on the thermoelastic properties of DNA adsorption films, the detection signals of microcantilevers and their temperature dependence. First, the Parsegian’s empirical potential based on a mesoscopic liquid crystal theory is employed to describe the interaction energy among coarse-grained DNA cylinders; then, the thought experiment method and the force balance method of nonlinear elastic network nodes are combined to characterize the elastic modulus, prestress and thermal expansion coefficient of DNA adsorption films; finally, based on an effective macroscopic continuum model for DNA microbeam deformation, we study the microcantilever resonance frequency shifts caused by DNA adsorptions and the temperature effect on the microcantilever static deflections, respectively. Results show that, compared with the convex-packaged, the re-entrant honeycomb packing pattern endows DNA adsorption films with a larger adjustable range of the elastic modulus and prestress, so as to make DNA-microcantilevers having an enhanced dynamic detection signal whereas a weaker response to temperature variation. These results are expected to provide a new option for the regulation design of DNA composite materials and microbeam sensors. Packing patterns play a key role in thermoelastic properties of DNA adsorption films and detection signals of microcantilevers. By constructing multiscale relations between DNA mesoscopic free energy and continuum microcantilever deformation, resonant frequency shift, the influence of packing patterns on thermoelastic properties of DNA adsorption films and detection signals of microcantilevers is investigated. Compared with the convex-packaged DNA adsorption film, the concave-packaged one endows a stronger dynamic biodetection signal, whereas a weaker response to ambient temperature variation due to a larger adjustable range of thermoelastic property.

Fatigue of buried dented pipeline specimens

This paper reports the results of fatigue tests performed on dented steel pipeline specimens that were buried and subjected to cyclic internal pressure. Hot-spot cyclic strain amplitudes were measured using two experimental techniques: Digital Image Correlation (DIC) and Fiber Optic Bragg Strain Gages (FBSG). First, full-field measurements were taken using DIC identified strain concentration sites that were potential locations or hot-spots for fatigue cracks to initiate. Close to these point-locations, measurements of strains using FBSG were also taken, and the results were then compared with the DIC results. These fiber gages were also used during the cyclic pressure loading process while the specimens were buried, in such a way as to monitor any possible influence that might be caused by soil coverture restricting the free deformation occurring in the dented areas. These cyclic strain values were used to demonstrate that a simple uniaxial Coffin-Manson fatigue equation that uses the universal exponents proposed by Manson and the circumferential strain amplitude can be used to predict the life of the dented specimens. Moreover, it was determined that the measured strains at the hot-spot locations were not influenced by the soil coverture.

Effect of multi-directional hot forging process on the microstructure and mechanical properties of Al–Si based alloy containing high amount of Zn and Cu

Abstract In this study, the hypoeutectic Al–7Si based alloy containing Zn and Cu was severely deformed with multi-directional forging (MDF) process at 200 °C. The samples were placed into an open die allowing the free deformation in only one direction and forged with hydraulic press at cumulative strains of 2.07, 4.14 and 6.21. The microstructural examinations were performed with X-ray diffractometer, optical, scanning and transmission electron microscopies while their strength properties were determined by tensile and hardness tests. MDF led to a refinement in α-Al grains, hard Si, Al7Cu2Fe and Al2Cu particles of crystallization origin. This process also provided a method for formation of secondary precipitates within the alloy's microstructure. It was determined that MDF increased the tensile properties of the alloy but decreased its hardness. On the other hand, this process converted brittle type fracture of homogenized alloy to ductile type. These results were explained in terms of grain boundary strengthening, precipitation hardening, refining of hard particles, and softening in matrix due to dynamic recovery and recrystallization mechanisms.

Theoretical and experimental research of steel reinforced concrete beams, strengthened by steel plates

This paper presents experimental and theoretical research for calculating of reinforced concrete beams strengthened bonded steel plates. The use of epoxy-bonded plates to strengthen existing or damaged steel reinforced concrete beams has been extensively researched. It has beenproven to be a useful and reliable method of increasing the ultimate flexural capacity of both damaged and undamaged members. The actualdeflection behavior in steel reinforced concrete beams is probabilistic in nature and requires statistical methods for a rational analysis.The strength of steel reinforced concrete bending structures are determined by the strength and deformability of concrete and steel, depend on the conditions of their joint deformation in the composition of steel reinforced concrete bending element. Steel reinforced concrete bending structures are used in public buildings are "flexible" elements, soin the extreme state when bending there are not only two neutral axes, but also a significant shift of the layers. The stress-strain state of the normal cross-section of a steel reinforced concrete element, in addition to the strength and deformability properties of concrete and steel depends on the degree of joint deformation of the concrete slaband steel beam in the plane of the joint. In steel reinforced concrete structures, steel and concrete with different strength and deformable properties are jointly deformed in a single cross-section underrelated conditions: free deformations of monolithic concrete are restrained by reinforcing mesh, steel profile shelf; free deformation of the steel loadbearing beam is prevented by monolithic concretewith reinforcement.As a result, between the steel profile and concrete, as well as between concrete and reinforcement in the normal cross section of the reinforcedconcrete element there is a complex stress state.

Centrifuge modeling of single pile-shallow foundation interaction in reverse fault

Both pile foundations and shallow foundations are deemed to be vulnerable to significant fault deformation. However, the pile foundation-shallow foundation interaction in dip-slip fault has never been studied, to the authors' knowledge. This study presents the results of two centrifuge tests, in which a shallow foundation and single piles are subjected to reverse faulting. The tests are compared with the ones from previous studies in the following conditions: free-field, with only a shallow foundation, and with only single piles. The results show that there is a significant interaction between the single piles and shallow foundations. The presence of single piles leads to larger displacements and rotations of shallow foundations. The shallow foundation affects the pile behaviors in two ways: 1) the rupture diversion caused by the shallow foundation leads to different magnitudes and distributions of soil displacements along the piles; 2) the shallow foundation prevents the free deformation of soil, resulting in increasing soil stress even after outcropping.

Influence of free torsion deformation modes on the microstructure and mechanical properties of commercially pure copper

The paper investigates the effect of the free torsion rate of cylindrical specimes of commercially pure copper (grade M1) on their deformed state, microstructure, and mechanical properties. The study of the microstructure was carried out by means of transmission electron microscopy and X-ray diffraction analysis in the central region and at the periphery of the deformed rod. The mechanical properties were evaluated by measuring the microhardness. It was found that an increase of the torsion rate, other things being equal, promotes more intensive strengthening and refinement of the microstructure.

Numerical modelling of the hydro-mechanical behaviour of unsaturated COx

This paper presents a modified Biot’s model for describing the hydromechanical behaviour of the Callovo-Oxfordian Argillite (COx) Claystone. The COx Claystone exhibits significant deformation during water desaturation/resaturation, and the standard Biot’s model is unable to predict the large shrinkage/swelling of the material. The authors then introduced an additional swelling/shrinkage law to simulate large deformations upon changes in water content. This added deformation law is calibrated against the difference between measurements from laboratory tests and predictions from the standard Biot’s model. The plastic-damage model, developed by Fichant et al. for concrete, is used to describe the mechanical behaviour of the solid skeleton of the COx Claystone. In particular, the stress–strain relation is described in a damage-based model, while the plastic behaviour relies on the Nadai criterion. The validation of the proposed model is performed by numerical simulation of (a) uniaxial compression tests under different relative humidities of 32, 44 and 76%; (b) triaxial compression tests at confining stresses of 0, 2, 6 and 12 MPa under relative humidity of 90%; (c) free deformation desaturation–resaturation paths; (d) resaturation swelling tests under a constant axial load; and (e) axial swelling pressure tests. Comparison of the results from the aforementioned numerical simulations with experimental data demonstrates the capability of the proposed model to describe accurately the hydromechanical behaviour of the COx Claystone.

Effect of heating rate on the free expansion deformation of concrete during the heating process

Concrete will expand after being heated at high temperature, and the thermal stress generated will cause cracks inside the concrete, which seriously endangers the safety of concrete. The influence of heating rate on the free expansion deformation of concrete during heating process was studied. Three heating rates were used to conduct high-temperature deformation test. The concrete specimens were heated from room temperature to the target temperature. The temperature in the furnace was maintained at the target temperature until the temperature in the center of the concrete specimen also reached the target temperature. The influences of heating rate on the linear expansion rate (LER) and thermal expansion coefficient (TEC) of concrete at different temperatures were analyzed. The results showed that in the range of 100–800 °C, the LER of concrete increased gradually with the increase of temperature, and the maximum value reached 1.336%. In the range of 100–400 °C, the deformation of concrete was slightly affected by the heating rate. In the range of 500–800 °C, the greater the heating rate, the greater the LER and TEC of concrete.

Damage control mechanism and seismic performance of a steel moment connection with replaceable low-yield-point steel double T-stub fuses

To achieve a damage-controllable and earthquake-resilient steel frame with more feasible and simple dissipative devices, an innovative steel moment-resisting connection with bolted ductile double T-stub fuses is developed in this work. These T-stubs with appropriate free deformation length in the stems, made of Low-Yield-Point (LYP) steels instead of ordinary steels, simultaneously behave as connectors, bearing elements, and replaceable dissipative fuses that benefit from the inherent excellent ductility, dissipation capacity, and fatigue performance of the LYP materials. The cyclic responses of the connections with LYP T-stubs subjected to different weakening strategies are explored and compared via extensive nonlinear numerical parametric analyses. Subsequently, the influences of the free deformation length and the weakened degree of the T-stub stem on the seismic performance and the structural fuse effect are evaluated. Finally, optimal design suggestions for this connection are proposed, which provide a reference for engineering applications. Analytical results demonstrate that properly designed LYP T-stubs with various weakened parameters can act as structural fuses by dissipating more than 90% of the system energy and concentrating most of the plasticity and damage, which effectively protect the main structural members from damage while being subjected to seismic excitations. Besides, due to low yield strengths, to achieve an identical weakened degree, the T-stubs made of LYP steels are stockier than the ones made of traditional or high-strength steels. This feature is able to avoid serious local buckling of stem plates and significant strength degradation, thus is conducive to the improvement of the ductility. By comprehensively considering the construction advantages, ductility, dissipation capacity, structural fuse performance, and material efficiency, LYP T-stub with a relatively thin stem is a more promising solution. The method of increasing the free deformation length of the stem effectively controls the damage within the LYP T-stubs, adequately improves the effect of structural fuses, and further lowers the required weakened degree; thus, the protection of primary frame members is achieved without excessively reducing the strength of the connection. Nevertheless, the T-stub fuses with overly-large free deformation lengths and thin stem plates tend to buckle substantially, resulting in significant strength deterioration that adversely decreases the ductility of the connections. As a result, an optimal solution with a satisfactory weakened degree and an appropriate free deformation length (αd = 0.8 and le = 1.0 bts) is suggested as a good compromise among the material efficiency, dissipation and ductility capacities, and structural fuse performance.

Two-stage grasp strategy combining CNN-based classification and adaptive detection on a flexible hand

Robotic autonomous grasping of food-related objects requires a nondestructive and safe grasp system for picking up various objects. A novel underactuated flexible hand consisting of a variable palm and four soft fingers is designed and manufactured to enhance the grasp space and deformability during interaction with unknown objects. A position deviation formulation is fitted to estimate the free bend deformation of soft fingers approximately through finite element analysis. A modular convolutional neural network is presented to identify the grasp directions, shape features and anticipated input pressure levels of novel objects for achieving multitarget classification. A vision-based adaptive detection method is proposed to obtain an accurate wrist orientation and the best grasp candidate by using two means of grasp planning (i.e. cross grasp planning and equidistant optimal grasp planning). A two-stage grasp strategy combining the classification and detection methods is developed as an effective solution to estimate the grasp configuration accurately. Results show that our flexible hand achieves 91.1% success rate in a physical grasp experiment on a UR robot, thereby demonstrating the reliability and adaptability of our grasp approach. The target object can be identified and detected within 0.263 s, which indicates the suitability of our approach in real-time applications.

Modeling of the ECAP Induced Strain Hardening Behavior in FCC Metals

In this work, a multi-scale framework that couples a crystal plasticity (CP) scheme with a continuum dislocation dynamics (CDD) model is proposed to predict the material behavior, microstructure and texture during equal channel angular pressing (ECAP) processes. The strain hardening in the model is considered to result from both the increase in the dislocation density and the grain fragmentation. The grain fragmentation process is modeled by accounting for the grain-grain interaction and incorporating the concept of the geometrically necessary dislocations (GNDs) into the mean free path of the dislocations. GNDs result from grain boundaries restricting the free deformation of a grain, causing an internal plastic deformation gradient that subsequently leads to grain fragmentation. A commercial Al-1100 billet, with rolling texture, is ECAP processed under Route C for different numbers of passes. Mechanical, microstructure, and texture characterization is achieved for the received and ECAPed materials. The proposed model parameters are calibrated using the tensile true-stress true-strain curves of the unprocessed material at two strain rates. The ECAP-processed aluminum microstructure, texture, dislocation densities and the mechanical properties are predicted.

Numerical Analysis of Single-Angle Steel Member Under Tension Force with Different End Deformations

Steel members with a single-angle cross-section are widely used, but some of their behaviours under loads are not considered by design codes, necessitating related research. This study is carried out on fifty steel single-angle members focused on the stress distribution behaviour and the ultimate axial load capacities under different end deformations through 3-dimensional Finite Element (FE) simulations and comparison with previous experimental findings. FE modeling is capable of modeling steel structures with high accuracy. Based on the results, the length of the angle affects neither the shape of the stress distribution nor the ultimate load capacity of the element. The end deformations affect the stress distribution on the member angle cross-section, including the ultimate load capacity. The end deformations which restricted deformations in the two directions perpendicular to the load axis are found to be optimal, with an average increase in load capacity by a factor of 1.96 for an equal angle and 2.21 for an unequal angle compared with the capacities calculated for single angles with deformations allowed in all directions. The appearance of a compression zone on the unconnected angle leg reduces the ultimate load capacity. The current design code (ANSI/AISC-360) can be adopted to calculate the ultimate load in the case of no deformation in the y-axis direction and no deformations in the x- and y-axis directions where the mean ratios of PNum/Pcode are 1.24 and 1.34 respectively. However, the code does not agree with the end deformations of free deformations and no deformation in the x-axis direction for either equal or unequal angles where the mean ratios of PNum/Pcode are 0.64 and 0.79 respectively, which is unsafe.