High Yield Strength Material Research Articles

Thermal equation of state of rhodium to 191 GPa and 2700 K using double-sided flash laser heating in a diamond anvil cell

The phase behavior of rhodium (Rh) metal has been studied to 191 GPa and 2700 K using a combination of room-temperature isothermal compression and double-sided flash laser heating experiments. The isothermal compression data have been fitted with a second-order adapted polynomial of order L equation of state (EoS) with best-fitting parameters of V0=13.764(2)Å3/atom, K0=258(3)GPa, and K′=5.36(9). Two-dimensional maps of the uniaxial stress component t are presented for Rh at different pressures showing the spatial distribution of the local stress state of a relatively high-yield strength material encased in a Bi pressure medium. In addition, a simple, thermal pressure equation-of-state model, based on a single Einstein temperature, has been fitted to the high-pressure-temperature data up to 2700 K at 148 GPa and ambient-pressure thermal expansion data up to 1982 K. Also determined are the best-fitting parameters to reproduce the thermal EoS within the two-dimensional integration software. The optimized parameters are V0=13.764Å3/atom, K0=260.54GPa, K′=5.114, αT=2.99×10−5 K−1, ∂αT/∂T=1.27×10−9 K−2, ∂K0/∂T=−6.43×10−5GPa/K, and ∂K′/∂T=−9.3×10−10K−1. Published by the American Physical Society 2024

Inter-laboratory study on the influence of 3D concrete printing set-ups on the bond behaviour of various reinforcements

This study investigates the influence of different printing set-ups and materials on the bond strength of reinforcement manually placed between 3D printed concrete layers. An identical experimental campaign was performed at two institutes in Switzerland and Italy. Each institute used its own printing process, which consisted either of a set on-demand mix or a high yield stress material. Two types of reinforcement (reinforcing bar Ø8 mm and a high strength steel wire Ø1 mm) and three production configurations (casting and printing with the reinforcement parallel or perpendicular to the printing direction) were investigated. The results showed high bond strength with only a limited influence of the fabrication method for the reinforcing bars. An increased bond was observed for the set on-demand approach compared to the high yield strength material. The comparison with existing models showed that the reinforcing bar bond strength of printed concrete varies slightly from conventional concrete. The high strength wires exhibited poor bond. Based on the gathered experiences, insights into the standardisation of testing for 3D concrete printing are discussed.

Grain refinement and mechanical properties improvements in a high strength Cu–Ni–Si alloy during multidirectional forging

Abstract Microstructure evolutions and properties variations of a high-strength Cu–Ni–Si alloy during multidirectional forging have been systematically investigated using microstructure characterizations and properties measurements. Experiment results indicated that nano-scale grains formed in the block samples having been multidirectional forged (MDF) at room/cryogenic temperatures. With the increase of the MDF cycle, the sub-grain structure was further refined to nano-grains with tens of nanometers in diameter. The ultimate tensile strength of the cryogenic temperature multidirectional forged sample was 1057 MPa, the yield strength was 923 MPa, and the fracture elongation was 7.2%. Rather than the solid solution strengthening from solutes impeding the glide of dislocation motion and the second phase particle precipitation strengthening from the Orowan looping, the grain boundary strengthening from the Hall–Petch effects plays crucial roles in strengthening the samples having been cryogenic multidirectional forged. These findings indicated that multidirectional forging is a passport to an ultrafine-grained structure and high yield strength material for the nuclear industry.

Transformation, partitioning and flow–deposit interactions during the run‐out of megaflows

AbstractFour megabeds (I to IV) were recognized throughout the Cerro Bola inlier, a glacially influenced depositional area of the Carboniferous Paganzo Basin, south‐western La Rioja Province, Argentina. Such anomalous thick beds are associated with the collapse of an unstable basin margin after periods of large meltwater discharge and sediment accumulation. Failure of these previously deposited sediments triggered mass flows and associated turbidity currents into the basin. Megabed I is up to 188 m thick and was deposited during a transgressive stage by re‐sedimentation of ice‐rafted debris. Also part of the transgressive stage, Megabeds II, III and IV are up to 9 m thick and are associated with a dropstone‐free period of flooding. Megabeds were subdivided into three divisions (1 to 3) that represent a spectrum of flow properties and rheologies, indicative of a wide range of grain support mechanisms. These divisions are proposed as an idealized deposit that may or may not be completely present; the Cerro Bola megabeds thus display bipartite or tripartite organization, each division inferred to reflect a rheologically distinct phase of flow. Division 1 is a basal layer that consists of clast‐supported and matrix‐supported, pebble conglomerate, rarely followed by weak normally graded to ungraded, very coarse‐ to coarse‐grained sandstone. This lower interval is interpreted to be the deposit of a concentrated density flow and is absent in bipartite megabeds. Division 2 is represented by a mud‐rich sandstone matrix with dispersed granule to pebble‐size crystalline and mudstone clasts. It also includes fragments of sandstone up to boulder size, as well as rafts of cohesive muddy material and wood fragments. Division 2 is interpreted to be a result of debris‐flow deposition. A debrite‐related topography, resulting from the freezing of high yield strength material, captures and partially confines the succeeding upper division 3, which fills the topographic lows and pinches out against topographic highs. Division 3 is rich in mudstone chips and consists of very coarse‐grained, dirty sandstones grading upward to siltstones and mudstones. It is interpreted to be a deposit of a co‐genetic turbidity current. Spectral gamma ray and petrographic analyses indicate that both debrite and co‐genetic turbidite have high depositional mud content and are of similar composition. One of the megabeds is correlated with an initial slump‐derived debris flow, which suggests that the mass flow becomes partitioned both at the top, generating a co‐genetic turbidity current and, at the base, segregating into a concentrated density flow that seems to behave as a gravelly traction carpet.

Comparison of three different methods for determination of damage in solid materials

Material failure is most often caused by cyclic fatigue loading. Prior to failure, material damage growth can be observed by means of various methods. Through experimental research, it has been determined that individual methods are appropriate only for specific types of materials and that analysis results also depend on the method of material loading. Therefore, a question is being raised on which method to choose for a specific material and method of loading. For this purpose, the paper presents the results of the damage initiation process and damage growth for high yield strength material Armox 500T, as well as for annealed low yield strength steel 42CrMo4. The measured data on material response are evaluated by means of three different methods which are based on the elastic modulus, plastic strain energy, and maximum stress.Parameters and damage values were obtained from the measurement data by means of various damage evaluation methods. After that, an overview was made of the differences between these methods. The results were used to determine the deficiencies and benefits of each method and the most appropriate method for subsequent tests was selected. The most frequently applied damage identification method, i.e. the elastic modulus method, proves to be inappropriate for high yield strength materials.

The Effect of Deposition Conditions on Adhesion Strength of Ti and Ti6Al4V Cold Spray Splats

Cold spray is a complex process where many parameters have to be considered in order to achieve optimized material deposition and properties. In the cold spray process, deposition velocity influences the degree of material deformation and material adhesion. While most materials can be easily deposited at relatively low deposition velocity (<700 m/s), this is not the case for high yield strength materials like Ti and its alloys. In the present study, we evaluate the effects of deposition velocity, powder size, particle position in the gas jet, gas temperature, and substrate temperature on the adhesion strength of cold spayed Ti and Ti6Al4V splats. A micromechanical test technique was used to shear individual splats of Ti or Ti6Al4V and measure their adhesion strength. The splats were deposited onto Ti or Ti6Al4V substrates over a range of deposition conditions with either nitrogen or helium as the propelling gas. The splat adhesion testing coupled with microstructural characterization was used to define the strength, the type and the continuity of the bonded interface between splat and substrate material. The results demonstrated that optimization of spray conditions makes it possible to obtain splats with continuous bonding along the splat/substrate interface and measured adhesion strengths approaching the shear strength of bulk material. The parameters shown to improve the splat adhesion included the increase of the splat deposition velocity well above the critical deposition velocity of the tested material, increase in the temperature of both powder and the substrate material, decrease in the powder size, and optimization of the flow dynamics for the cold spray gun nozzle. Through comparisons to the literature, the adhesion strength of Ti splats measured with the splat adhesion technique correlated well with the cohesion strength of Ti coatings deposited under similar conditions and measured with tubular coating tensile (TCT) test.

Critical crack size that causes retardation of short fatigue crack by single overload

ABSTRACTThe effect of crack length on the retardation of fatigue crack propagation caused by single overload was investigated using carbon steels S25C and S45C. The retardation and crack arrest occurred even in short cracks ranging from 50 to several hundred microns. In case retardation occurs, it is caused by the increase of crack closure stress as in a long crack. The occurrence of retardation, however, showed a complex dependency on crack length, yield strength of material and the value of baseline stress ratio R. At stress ratio R =−1, retardation did not occur for very short crack as short as 50 μm in the case of low yield strength material. This was because the increase of crack closure stress was prevented by the compressive stress component of baseline load. The plastically deformed layer near the crack tip was collapsed by the compressive stress of baseline load, which prevented the development of crack closure. In the case of high yield strength material, however, retardation occurred even in 50 μm crack. On the contrary at R = 0, retardation in the low yield strength material occurred even in 50 μm crack. The prevention of increase of crack closure did not occur in the case of R = 0. As a consequence, retardation basically occurs even in short crack as short as 50 μm unless the development of crack closure is impeded.

Characterization and Mechanical Behavior of Nanoporous Gold

AbstractHere we present current issues in understanding the mechanical behavior of nanoporous foams as a new class of high yield strength / low density materials. Gold nanoporous foams are used for a systematic study of mechanical properties since they can be synthesized with a wide range of ligaments sizes and densities. Preliminary tests demonstrate that a) Au foams have a fracture behavior dictated by the ligament size, and b) nanoporous Au is a high yield strength material.

A micromechanical analysis of the ductile-brittle transition at a weld

The competition between brittle and ductile modes of failure is analyzed in a weld specimen subject to dynamic transverse loading. Full transient analyses under plane strain conditions are carried out. The material response is characterized by an elastic–viscoplastic constitutive relation for a porous plastic solid, with adiabatic heating due to plastic dissipation and the resulting thermal softening accounted for. The onset of cleavage is assumed to occur when a critical value of the maximum principal stress is attained. Different levels of undermatched or overmatched welds are analyzed. It is found that high flow strength in the heat affected zone (HAZ) can have a strong influence on the transition temperature, but this can differ significantly between undermatched and overmatched welds. A comparison of a low strain hardening material with a high strain hardening material shows that strain hardening also strongly affects the transition behavior. In addition, the transition behavior is compared for a high yield strength material and a low yield strength material, with a proportional change in the critical stress for cleavage.

溶接残留応力下における疲労き裂伝ぱ挙動に及ぼす塑性変形効果

Crack closure behavior in fatigue crack propagation process is induced by plastic deformation near crack. In the present paper, the effect of plastic deformation on fatigue crack closure in low strength material and its welded joint was studied. The results obtained are as follows. Crack closure was caused by plastic deformation near crack surface. Generally, the crack opening ratio in high yield strength material was higher than that in low yield one. This tendency results from a low degree of deformation near crack surface. In addition, in welded joint, the crack propagation rate was higher than the mother metal, though the crack opening ratio was almost 1 by the effect of residual stress. This was explained by the effect of restraint for plastic deformation, which was induced by the existence of compressive stress field ahead of crack.

低降伏点材料とその溶接継手部における疲労き裂開閉口挙動と塑性変形効果について

Crack closure behavior in fatigue crack propagation process was induced by plastic deformation near crack. In the paper, the effect of plastic deformation on fatigue crack closure in low strength material and its welded joint was studied.The results are as follows. Crack closure would be caused by plastic deformation near crack surface. Generally, crack opening ratio in high yield strength material is higher than that in low yield one. This tendency based on the degree of deformation near crack surface. In addition, in welded joint, crack propagation rate was higher than mother metal, though crack opening ratio showed almost 1 by the effect of residual stress. This could be explained by the effect of restrain for plastic deformation, which was induced by existence of compresive stress field ahead of crack.

Study on Electron Beam Welding Procedure for Pressure Hull of Deep Submergence Research Vehicle

The pressure hull for deep submersible has to cope with the trade-off subject of load carrying capacity and minimum weight at the same time. For this reason, spherical shell has been normally adopted for the pressure hull. Besides this, high yield strength materials and high-precision manufacturing are indispensable for it.The authors have already confirmed that GTA welding is effective for the pressure hull of 6, 000 m class of 10 Ni-8 Co steel. However recently, electron beam welding, which has the possibility to reduce welding distortion in comparison with GTA welding, has come to withstand this objective.The authors, in this paper, have estabilished the effectiveness of EBW for the pressure hull of 6, 000 m class of 10 Ni-8 Co steel.

１０Ｎｉ‐８Ｃｏ高じん性超高張力鋼を用いた潜水調査船耐圧かくの電子ビーム溶接に関する研究

The pressure hull for deep submersible has to cope with the tradeoff subject of the load carrying capacity and the minimum weight at the same time. For this reason, spherical shell has been normally adopted for the pressure hull. Besides this, high yield strength materials are used for it.The authors have already confirmed that GTA welding is effective for the pressure hull of 6, 000 m class of 10Ni-8Co steel. However recently, electron beam welding, which has the possibility to reduce welding distortion in comparison with GTA welding, has come to withstand this objective.The authors, in this paper, have established the effectiveness of the EBW for the pressure hull of 6, 000 m class of 10Ni-8Co steel.

Structure and mechanical properties of Al/Al xO y vacuum- deposited laminates

High yield strength materials can be fabricated by many techniques. A method proposed by Koehler is to alternate thin layers of a high shear modulus material with thin layers of a low shear modulus material. The layers must be less than one hundred atomic layers in thickness and must be single crystals of similar lattice spacing epitaxially grown on top of each other. The mechanical effect is to inhibit dislocation formation and the mobility of dislocations through the solid. The stress required to move a dislocation through the laminate can be of the order of 1% of the lower modulus material. A novel technique has been developed to produce a laminate of Al/Al x O y by a pulsed gas process in an electron beam gun system. Samples of 25 μm and thicker have been readily produced. The surface finish of the growing deposit appears to remain as smooth as the glass substrate. The tensile testing data for layer spacings of 50–1200 nm show that the material obeys a Hall-Petch relation for yield strength. The friction stress was measured directly on a pure vapor-deposited sample at 27 MPa. The K value was found to be 0.086 MN m - 3 2 .