Limited Ductility Research Articles

Evaluation of Equivalent Cladding Reacted parameters of Cr-coated claddings oxidized in steam at 1200 °C in relation with oxygen diffusion/partitioning and post-quench ductility

Cr-coated M5Framatome1 cladding materials are studied and developed within the CEA-Framatome-EDF French nuclear fuel joint program as Enhanced Accident Tolerant Fuel claddings for Light Water Reactors. The objective of this paper is to bring some insights into the relationship between Equivalent Cladding Reacted (ECR) parameters, oxygen diffusion/partitioning and Post-Quench (PQ) ductility of Cr-coated M5Framatome fuel claddings oxidized in steam at 1200 °C.The physical meaning of the ECR parameter, evaluated experimentally from the measured Weight Gain (WG) or calculated using time and temperature correlations such as the Baker-Just (BJ) or Cathcart-Pawel (CP) kinetics correlations, is discussed in the light of the benefit brought by Cr coating to oxidation resistance of cladding. As shown in this article, when applied to the Cr-coated M5Framatome materials, the “experimental” ECR derived from WG does not have the same physical meaning than for the uncoated cladding materials. As discussed in the paper, this is fundamentally due to the use of the ECR as a surrogate for retained ductility for uncoated claddings, and to the differences between uncoated and Cr-coated cladding in the high temperature (HT) steam oxidation processes and partitioning of the oxygen between the different layers of the oxidized cladding.It is shown in this article that Cr-coated M5Framatome cladding brings significant additional time-at-temperature before full embrittlement of the cladding after one-sided oxidation at 1200 °C and quenching, compared to uncoated materials. The oxidation times and associated Baker-Just ECR (BJ-ECR) values, above which the cladding becomes brittle after low temperature quenching, are respectively ten times and three times higher than the ones for the uncoated reference cladding. When analyzing the PQ ductility of the Cr-coated M5Framatome cladding using a similar methodology as the one used to derive the ECR criterion for uncoated cladding, the 1–2% ductility limit corresponds to a BJ-ECR of about 50% or higher, for a 12-15 μm-thick Cr-coated cladding tested herein.

Simple equations for predicting the rotational ductility of fiber-reinforced-polymer strengthened reinforced concrete joints

Achieving a certain limit of rotational ductility in retrofitted reinforced concrete (R.C) joints is very important in the design of earthquake-resistant structures. Strengthening of R.C joints using wraps of fiber-reinforced polymers (FRP) is a common attractive technique and has an effect on the ductility of such joints. This study focuses on developing simple conceptual equations to predict the ductility of exterior reinforced concrete (R.C) beam-column joints as a function of the applied FRP. The equations are derived based on statistical regression through parametric study using results from a high-fidelity finite element model created using ABAQUS. The validated model includes material and geometric nonlinearities, in addition to the use of realistic nonlinear contact behavior between FRP and concrete. The proposed simple equations can be used as an initial conceptual design step for checking the adequacy of R.C beam-column joints in seismic design of R.C buildings. The proposed equations consider FRP, relative column-to-beam inertia, and transverse reinforcement in the beam and joint as the main parameter. This study defines the types of failure based on the ductility, and it develops the equations for ductile and brittle failures for both CFRP-strengthened joints and non-strengthened joints. This research confirms quantitatively the effectiveness of using CFRP to increase the ductility in most cases of the R.C beam-column joints. However, contribution of the CFRP is limited for some cases.

Ductility Limit Diagrams for Superplasticity and Forging of High Temperature Polycrystalline Materials

A mechanistic understanding of the ductility limit diagrams is of critical importance, but it still remains elusive for a multitude of high temperature materials processing techniques, such as superplastic forming and hot forging. The relevant failure modes for the former are necking at high strain rates and intergranular cavitation at low strain rates, while those for the latter include the competition between longitudinal fracture and shear band. The comparison between the Arrhenius processes for grain boundary diffusion and grain interior creep defines a length scale that dictates whether the grain boundary cavity growth is diffusive or creep-constrained. A quantitative assessment of these damage evolution processes leads to the delineation of the dominant parametric spaces for individual failure modes, and thus superplasticity and forging limit diagrams are derived and compared to available experiments in literature.

Influence of processing factors on the sheared-edge formability of vanadium bearing dual-phase steels produced using continuous galvanizing line simulations

Dual-phase steels are commercially attractive since they offer good formability at a high strength and reasonable cost. In addition to high strength, these steels also exhibit high “n-values” and high uniform and total tensile elongations. However, one limitation in the application of high-strength dual-phase steels is the fairly limited ductility observed during sheared-edge stretching or punched hole expansion. Therefore, successful high-strength dual-phase steels must have controlled microstructures in order to achieve the desired performance. The failure mechanism observed during stretching of the sheared edge is closely related to the microstructures (i.e., amount, hardness, size and distribution of the different phases and microconstituents), and the cracks were found to initiate predominately at the interphase interfaces separating the ferrite and the martensite. In the present research, the influence of three main variables on the hole expansion ratio (HER) behavior was explored: the metallurgical condition going into the continuous galvanizing line (CGL), different post-anneal CG line thermal processing paths and the influence of vanadium. Depending on conditions, all three variables can influence the sheared-edge ductility as determined in the hole expansion test. Suggestions for improving the sheared-edge ductility while maintaining adequate strength are presented.

Flexural and Abrasion Behaviour of Flooring Tile with Roselle Fiber

In the world-wide research is being conducted concerning the use of fibers. This research aims to analyze the strength and behavior of natural fiber tiles relative to the conventional tiles. The researchers are exploring new materials that expand choices of flooring tiles. In this researcher produces tiles using Roselle fibers. India is the country having largest producer of roselle fiber. In this study Roselle fiber is used in two techniques, one in the form of mesh and another is mixing it with mortar. For both techniques the percentage of natural fiber was different. Because of increasing environmental problems, scientists and researchers are using natural fiber instead of synthetic fiber as the main component in composites. Cement mortar has very low tensile strength, limited ductility and little resistance to cracking. This study aims to compare flexural strength and abrasion of tiles by using natural fiber tile and conventional tile.

Mechanical Properties of Glass Fiber Concrete with Different Dosages of Glass Fiber

Conventional concrete i.e. the concrete generally has low tensile strength with limited ductility and low resistance towards cracking. The micro cracks that are developed internally are inherent among concrete and can be explained with the help of propagation of that micro cracks due to its inferior tensile strength. Different fibers, added at a certain percentage of concrete known to improve the deformation properties of concrete along with the plasticity against crack resistance, such as flexural strength. Mainly concrete & ferroconcrete research has been moved to steel fibers, and glass fibers have recently become more available, with no corrosion problems associated with glass fibers. This article describes an experimental study of the usage of glass fibers in the structural concrete. High-dispersion CEM-FILL fiberglass of 14 μm diameter with an aspect ratio of 857 was used at a dosage of 0.33% to 1% by weight in concrete and its mechanical properties such as compressive strength, flexural strength and modulus of elasticity.

Microstructure evolution and mechanical properties of Ti–8Nb–2Fe-0.2O alloy with high elastic admissible strain for orthopedic implant applications

A Ti–8Nb–2Fe-0.2O (wt.%) alloy with high strength, high elastic admissible strain (δ) and low cost was designed using d-electron theory combined with electron-to-atom ratio (e/a‾) approach. Interstitial oxygen was introduced to strengthen the matrix of the alloy. The β-solution treated alloy was mainly composed of α″ martensite with internal {111}α″ type I nano-twins. The α″ martensite with hexagonal-like crystal structure caused by interstitial oxygen showed a high strength of 1.1 GPa but limited ductility. The alloy generated equiaxed fine-grained α phase embedded by β matrix via hot rolling and subsequent annealing in α + β phase field. The obtained alloy indicated a good combination of mechanical properties with ultimate tensile strength, Young’s modulus, ductility and δ value of 1029 MPa, 74 GPa, 21% tensile elongation and 1.32%, respectively. These findings demonstrate that interstitial oxygen and martensitic nano-twins can be used to strengthen the soft α″ martensite and high elastic admissible strain can be obtained by formation of equiaxed fine-grained α phase embedded by β matrix in this Ti–8Nb–2Fe-0.2O alloy for orthopedic implant.

High Temperature and Corrosion Properties of A Newly Developed Fe-Al-O Based OPH Alloy

Fe–Al–O-based materials are currently undergoing a great deal of development because of their many special properties. However, lack of strength at high temperatures, limited ductility at ambient temperatures and corrosion resistance have hindered a wider application of these materials. Recently, a new Fe–Al-based oxide precipitation hardened (OPH) steel was developed by the authors to improve the mechanical properties and oxidation resistance. The new OPH alloys are produced by dissolving a specific amount of oxygen in the matrix during mechanical alloying followed by precipitation of fine dispersion of aluminum or yttrium oxides during hot consolidation. A series of tests was performed to evaluate the thermomechanical properties and corrosion resistance in a 3.5% NaCl solution. The results show improved corrosion resistance, as well as mechanical properties, while the production costs of this material are lower than for traditional materials.

Improvement of mechanical properties by means of titanium alloying to steel teeth used in the excavator

The effect of Ti addition (0.15 and 0.20 wt%) on mechanical properties and wear resistance of steel excavator bucket teeth was investigated. Teeth were produced by commercial sand casting technique. After production normalizing, hardening, and tempering heat treatment procedures were applied to the teeth. Lath martensitic microstructure was observed and small amount of carbide particles were present in the microstructures of Ti containing ones. In addition, small amount of hard and brittle TiN particles were observed in the microstructure of 0.20 wt% Ti containing teeth. The best mechanical properties were obtained for 0.15 wt% Ti containing teeth with considerably high abrasive wear resistance. However, 0.20 wt% Ti containing teeth exhibited worst abrasive wear resistance and limited ductility due to the formation of TiN particles.

Fracture Investigation in Draw Bending of AZ31B Sheets using Fuzzy Logic Prediction

Automotive and aircraft industries are facing an increased demand of light-weighted materials for reducing fuel consumption and CO2 emissions. Magnesium alloy sheets are considered in manufacturing components of complex geometries and with flexible processes. Fracture investigation of AZ31B alloy sheets is of interest in continuous bending processes to achieve better formability. Certain forming processes of AZ31B sheets are restricted due to its limited ductility at room temperature. Draw bending of AZ31B sheets provides us the necessary forming state to investigate fracture limits. Our investigation relies on data extracted from draw bending tests organised according to a design of experiments plan. The experimental studies were conducted for different punch radii, traverse speeds and rolling directions. The predicted fracture behavior via Fuzzy Logic provides essential data to the setup procedures needed for our subsequent research, which is focusing on reducing the limitations of AZ31B sheets formability.

Mechanical Properties and Failure Behaviour of Architected Alumina Microlattices Fabricated by Stereolithography 3d Printing

The mechanical behaviour of Simple Cubic, Octet Truss and Kelvin Cell alumina microlattices with solid struts was systematically studied through experiments and simulations. Our results showed that the specific mechanical properties of the microlattices were the best for Simple Cubic, worst for Kelvin Cell, and followed Ashby’s power law well at small relative densities (≤ 0.3). At higher relative densities, the power law changed as joint deformation became increasingly important to overall lattice mechanics. The Simple Cubic lattices failed in a column-by-column manner from the sides inwards to the centre, while fracture in Octet Truss and Kelvin Cell lattices took place predominantly along the diagonal (110) plane. This was confirmed to be due to the interplay between the fixed top and bottom boundaries with the free sides of the lattices. At low relative densities, the microlattice struts were also observed to fail in a sequential, localized manner, in contrast to the simultaneous fracture observed at higher relative densities. Compared to current materials, the alumina microlattices exhibited outstanding specific moduli and specific strength, as well as limited ductility in the form of pseudoplastic strains (0.1% - 0.5%). Therefore, alumina microlattices are expected to be an invaluable addition to the material catalogue for engineering designers.

Prediction of necking in HCP sheet metals using a two-surface plasticity model

In the present contribution, a two-surface plasticity model is coupled with several diffuse and localized necking criteria to predict the ductility limits of hexagonal closed packed sheet metals. The plastic strain is considered, in this two-surface constitutive framework, as the result of both slip and twinning deformation modes. This leads to a description of the plastic anisotropy by two separate yield functions: the Barlat yield function to model plastic anisotropy due to slip deformation modes, and the Cazacu yield function to model plastic anisotropy due to twinning deformation modes. Actually, the proposed two-surface model offers an accurate prediction of the plastic anisotropy as well as the tension–compression yield asymmetry for the material response. Furthermore, the current model allows incorporating the effect of distortional hardening resulting from the evolution of plastic anisotropy and tension–compression yield asymmetry. Diffuse necking is predicted by the general bifurcation criterion. As to localized necking, it is determined by the Rice bifurcation criterion as well as by the Marciniak & Kuczynski imperfection approach. To apply both bifurcation criteria, the expression of the continuum tangent modulus associated with this constitutive framework is analytically derived. The set of equations resulting from the coupling between the Marciniak & Kuczynski approach and the constitutive relations is solved by developing an efficient implicit algorithm. The numerical implementation of the two-surface model is assessed and validated through a comparative study between our numerical predictions and several experimental results from the literature. A sensitivity study is presented to analyze the effect of some mechanical parameters on the prediction of diffuse and localized necking in thin sheet metals made of HCP materials. The effect of distortional hardening on the onset of plastic instability is also investigated.

Shear Strength of Exterior Beam-Column Joints with Limited Ductility Details

AbstractThe seismic performance of exterior beam-column joints in low-rise buildings with limited ductility details was investigated. Seven exterior beam-column connection specimens were prepared f...

Meso-scale modelling of semi-solid deformation in aluminum foundry alloys: Effects of feeding and microstructure on hot tearing susceptibility

Abstract In the context of hot tearing susceptibility, the semi-solid constitutive behaviour of two commercially important foundry aluminum alloys at high solid fraction has been simulated. The numerical methodology combines solid mechanics, computational fluid dynamics, and microstructure modelling, i.e a meso-scale multi-physics approach. Feedable and un-feedable domains with different microstructures including equiaxed globular, equiaxed dendritic, and combined dendritic and eutectic were developed. Considering that it is the combined effects of a lack of liquid feeding and limited semi-solid ductility that contribute to hot tearing formation, the effect of feeding and mechanical deformation are studied and discussed. The model demonstrates that the microstructure type and the eutectic formation also have a considerable effect on the liquid channels pressure drop and semi-solid bulk stress and strain, and consequently on hot tearing.

Zr-Co-Al bulk metallic glass composites containing B2 ZrCo via rapid quenching and annealing

As a promising remedy for overcoming the limited ductility and work softening of bulk metallic glasses (BMGs), BMG composites incorporating a B2 crystalline phase have attracted considerable attention. Here, we explore the formation of Zr-Co-Al BMG composites by quenching alloys Zr55Co31Al14, Zr54.5Co33.5Al12, Zr53.5Co36.5Al10, Zr52.5Co37.5Al10, and Zr43Co43Al14. We found the first alloy fully amorphous whereas the fifth was fully crystallized upon quenching. The other three were quenched to generate composite structures, with a higher fraction of B2 ZrCo phase with increasing Co/Zr ratio and decreasing Al content. For comparison, the formation of B2 ZrCo in annealed Zr55Co31Al14 was also studied. For both approaches the influence of crystalline phases on hardness was examined.

Fracture Toughness of Cold Sprayed Pure Metals

The study of fracture toughness of pure Al, Cu, Ni and Ti deposited by cold spray was performed in order to obtain a fundamental understanding of the damage process and quantify the material performance. Rectangular specimens cut from self-standing deposits with fatigue pre-cracks were tested in three-point bending. The KIC values were obtained from J-R curves following the ASTM E1820 standard. The stress–strain behavior of the tested material was obtained from supplementary four-point bending. The cold spray deposits exhibited significantly lower fracture toughness than the corresponding wrought materials. The reduction was more pronounced for coatings with limited ductility (Ti and Cu), where the fracture toughness reached less than 12% of the wrought counterpart only. The higher ductility coatings of Al and Ni possessed fracture toughness of 18–25% of the wrought reference materials. The performed fractographic analysis revealed inter-particular decohesion as the major failure mode.

Effect of thermal and thermo-mechanical processing on Mg-Sn-Zn alloy and understanding structure-property correlation

In this study, Mg-5Sn-5Zn alloy was fabricated and conditioned by thermal and thermo-mechanical treatment. The microstructure and phase evolution of the processed alloy were investigated by Optical microscope and X-ray diffraction studies. The tensile test results show that hot extruded alloy shows higher strength with limited ductility than the as-cast and homogenized Mg-5Zn-5Sn alloy. While homogenized alloy shows better ductility 4fold better than the extruded and 2fold than as-cast alloy. Electrochemical polarization test was conducted in a NaCl solution. The corrosion rate depends on Mg2Sn and MgZn2 to achieve high corrosion resistance, the tin and zinc should dissolve in Mg- matrix that is the homogenized sample at 400 °C for 13hrs has the lower corrosion rate.

Response of Mid-Rise Reinforced Concrete Frame Buildings to the 2017 Puebla Earthquake

The response of mid-rise reinforced concrete (RC) buildings in Mexico City after the 2017 Puebla Earthquake is assessed through combined field and computational investigation. The Mw 7.1 earthquake damaged more than 500 buildings where most of them are classified as mid-rise RC frames with infill walls. A multinational team from Colombia, Mexico, and the United States was rapidly deployed within a week of the occurrence of the event to investigate the structural and nonstructural damage levels of over 60 RC buildings with 2–12 stories. The results of the study confirmed that older mid-rise structures with limited ductility capacity may have been shaken past their capacity. To elucidate the widespread damage in mid-rise RC framed structures, the post-earthquake reconnaissance effort is complemented with inelastic modeling and simulation of several representative RC framing systems with and without masonry infill walls. It was confirmed that the addition of non-isolated masonry infills significantly impacts the ductility capacity and increases the potential for a soft-story mechanism formation in RC frames originally analyzed and designed to be bare systems.

Influence of Hybrid Fibre on the Mechanical Properties of Concrete

This study presents the experimental investigation carried out to study the mechanical properties of concrete with and without the addition of fibres to it.d Concrete is the most consumed material in the world which has the property of strong in compression and weak in tension. Also plain concrete possess very limited ductility and little resistance to cracking. Hence fibres are introduced in the concrete to improve the tensile strength & brittleness of the concrete. These fibres which are closely spaced and dispersed uniformly in the concrete arrest the micro and macro cracks and improve the tensile strength of concrete. Concrete admixed with such fibres are known as Fibre Reinforced Concrete. The combination of two (or) more fibres called as Hybridization is carried out in this work. M25 grade concrete is designed as per IS 10262:2009 with the volume fraction of 0-1.5%. The workability of the concrete is affected due to the addition of fibres and hence super plasticizers are added to the concrete. The fibres considered for the study are (i) Crimped Steel Fibre (0-1.5%) and (ii) Shortcut Glass Fibre (0.1-0.2%). The behaviour of the hybrid fibre reinforced concrete is investigated by conducting compressive strength test on cube specimen of size 150mmx150mmx150mm and split tensile strength test on cylinder specimen of size 150mm diameter and 300mm height. From the experimental results, the optimum fibre combinations for maximum compressive strength and spilt tensile strength of concrete are identified.

Achieving excellent ductility in high-strength Mg-10.6Gd-2 Ag alloy via equal channel angular pressing

Excellent ductility and high strength were achieved in the Mg-10.6Gd-2Ag (wt. %) alloy via an industrial-scale equal channel angular pressing (ECAP). The ECAP alloy exhibits an extremely high ductility (elongation of 22.6%) as well as a high strength (ultimate tensile strength of 417.2 MPa). This ductility exceeds the known ductility limit of the existing high-strength Mg-RE wrought alloys. After peak-aging, an optimal ultimate tensile strength of 460.3 MPa is obtained accompanied by a moderate ductility (elongation of 8.9%). The excellent ductility originates from the fine and full DRXed microstructure, which involves the homogenous and fine equiaxed grains, the cobblestone-like submicron particles distributed along the α-Mg grain boundaries, and the weak and approximately random texture. The submicron particles are identified as the dynamically precipitated Ag-containing Mg5Gd-typed compound. After peak-aging, co-existence of the high-density basal γ’’ plates and the relatively low-density prismatic β′ plates are observed in the α-Mg grain interior, and an interfacial phase is found to segregate in some α-Mg grain boundaries. The high strength is mainly ascribed to the synergistic effect of the fine grains, the high-frequency high angle boundaries, and the additional co-precipitates of the β′ plates and the γ’’ plates in the aged alloy.