Specimen Axis Research Articles

Three different approaches for damage domain characterization in disordered materials: Fractal energy density, b-value statistics, renormalization group theory

Material characterization is usually based on the stress–strain constitutive laws directly derived from the load–displacement relations of uniaxial compression tests. This approach, which implies a uniform distribution of deformation along the specimen axis and an energy dissipation within a volume, does not permit to correctly describe the mechanical behavior and the damage evolution by varying the structural size and slenderness.In this paper, three different approaches are used to evaluate the physical dimension of the damage domain in disordered materials subjected to uniaxial compression. The energetic and the statistical methods are based on the acoustic emission monitoring technique, whereas the renormalization group procedure is based on the assumption of anomalous physical dimensions for the material properties. The three approaches agree very well in the determination of the damage domain fractal dimension.

<sup>210</sup>Pb-<sup>226</sup>Ra chronology reveals rapid growth rate of <i>Madrepora oculata</i> and <i>Lophelia pertusa</i> on world's largest cold-water coral reef

Abstract. Here we show the use of the 210Pb-226Ra excess method to determine the growth rate of two corals from the world's largest known cold-water coral reef, Røst Reef, north of the Arctic circle off Norway. Colonies of each of the two species that build the reef, Lophelia pertusa and Madrepora oculata, were collected alive at 350 m depth using a submersible. Pb and Ra isotopes were measured along the major growth axis of both specimens using low level alpha and gamma spectrometry and trace element compositions were studied. 210Pb and 226Ra differ in the way they are incorporated into coral skeletons. Hence, to assess growth rates, we considered the exponential decrease of initially incorporated 210Pb, as well as the increase in 210Pb from the decay of 226Ra and contamination with 210Pb associated with Mn-Fe coatings that we were unable to remove completely from the oldest parts of the skeletons. 226Ra activity was similar in both coral species, so, assuming constant uptake of 210Pb through time, we used the 210Pb-226Ra chronology to calculate growth rates. The 45.5 cm long branch of M. oculata was 31 yr with an average linear growth rate of 14.4 ± 1.1 mm yr−1 (2.6 polyps per year). Despite cleaning, a correction for Mn-Fe oxide contamination was required for the oldest part of the colony; this correction corroborated our radiocarbon date of 40 yr and a mean growth rate of 2 polyps yr−1. This rate is similar to the one obtained in aquarium experiments under optimal growth conditions. For the 80 cm-long L. pertusa colony, metal-oxide contamination remained in both the middle and basal part of the coral skeleton despite cleaning, inhibiting similar age and growth rate estimates. The youngest part of the colony was free of metal oxides and this 15 cm section had an estimated a growth rate of 8 mm yr−1, with high uncertainty (~1 polyp every two to three years). We are less certain of this 210Pb growth rate estimate which is within the lowermost ranges of previous growth rate estimates. We show that 210Pb-226Ra dating can be successfully applied to determine the age and growth rate of framework-forming cold-water corals if Mn-Fe oxide deposits can be removed. Where metal oxides can be removed, large M. oculata and L. pertusa skeletons provide archives for studies of intermediate water masses with an up to annual time resolution and spanning over many decades.

Analysis of Fracture Mechanics Tests on Opalinus Clay

Many studies have recently been conducted to evaluate various mechanical characteristics of the Opalinus Clay (OPA) formation in view of its potential use as the hosting rock for the Swiss nuclear waste repositories. Its sedimentary bedding makes OPA a transversely isotropic rock and its directional mechanical properties need to be measured. This paper reports on an experimental and computational approach that was adopted to define the parallel-to-bedding fracture mechanics (FM) parameters of OPA in Mode-I. OPA cores from Mont Terri Underground Research Laboratory (URL) were submitted to laboratory tests on notched semi-circular specimens under three-point bending (SCB). In these tests, crack propagation is forced along the notch direction. However, the 45° bedding inclination of the specimen axis frequently deviated the crack from the expected direction. An analysis of the SCB tests was performed by means of non-linear FM techniques and the pertinent Mode-I parameters along the bedding were estimated.

EFFECT OF MICROSTRUCTURE ON FATIGUE PROPERTIES OF Al ALLOYS

Effects of a texture and atmospheric moisture on fatigue properties of an extruded bar and a drawn one of age-hardened Al alloy were investigated under rotating bending in relative humidity of 25% and 85%. The extruded alloy had a marked texture of (111) plane, but the drawn one did not have a specified orientation. Fatigue strength was largely decreased by high humidity in both alloys. The decrease in fatigue strength was larger in the extruded alloy than in the drawn one. Macroscopic growth mode of a crack of the extruded alloy was a shear mode inclined 35° to the specimen axis in high humidity, though those were a tensile mode in low humidity and in both humidity in the drawn alloy. The fracture surface yielded by the shear mode crack was occupied by many slip planes and voids and was (100) plane, though the fracture surface formed by the growth of a tensile mode crack was mainly covered with striations. The shear mode crack was related to the marked texture of the extruded Al alloy and promoted by high humidity.

Physical Simulation of Grooved Axis Warm Surface Rolling

The experimental design and implementation, as well as the fatigue life test of the steel C45 grooved axis warm surface rolling, have been carried out in this paper. The focus of the experiment is to study the effect of the different amount of rolling reduction and surface temperature on the fatigue life of the specimen axis.The experimental specific condition is at different temperature 20°C, 100°C, 200°C and 300°C with surface rolling reduction 0.03 mm, 0.06mm, 0.10mm, and 0.15mm respectively. The simulation results showed that the warm surface rolling process can significantly improve the fatigue life of the specimen axis; and there exist a corresponding optimum rolling reduction, in this case the fatigue life of the specimen axis achieves maximum, at different warm rolling temperatures. Finally the preferred processing parameter at 300°C with 0.15mm surface rolling reduction is obtained. This study has certain reference value for steel C45 the crankshaft undercut surface rolling.

Influence of Al-Si Diffusion Coating on Low Cycle Fatigue Properties of Cast Superalloy Inconel 738LC at 800 °C

High temperature low cycle fatigue behaviour of cast nickel-based superalloy Inconel 738LC in as-received condition and coated with an Al-Si diffusion layer was studied. The Al-Si protective layer was deposited on the gauge section of cylindrical specimens using the slurry technique. Fatigue tests were performed on cylindrical specimens under total strain control in symmetrical cycle at 800 °C in air. The coating has a beneficial effect on fatigue life in the low amplitude domain. The stress response of the coated material is higher for high amplitudes in comparison with the uncoated one. Fracture surfaces and sections parallel to the specimen axis have been examined to study fatigue damage mechanisms.

Recycled carbon fibre-reinforced polypropylene thermoplastic composites

Comingled carbon fibre (CF)/polypropylene (PP) yarns were produced from chopped recycled carbon fibres (reCF) (20 mm in length, 7–8 μm diameter) blended with matrix polypropylene staple fibres (60 mm in length, 28 μm diameter) using a modified carding and wrap spinning process. Microscopic analysis showed that more than 90% of the reCF were aligned along the yarn axis. Thermoplastic composite test specimens fabricated from the wrap-spun yarns had 15–27.7% reCF volume content. Similar to the yarn, greater than 90% of the reCF comprising each composite sample made, showed a parallel alignment with the axis of the test specimens. The average values obtained for tensile, and flexural strengths were 160 MPa and 154 MPa, respectively for composite specimens containing 27.7% reCF by volume. It was concluded that with such mechanical properties, thermoplastic composites made from recycled CF could be used as low cost materials for many non-structural applications.

High cycle fatigue behavior of the second generation single crystal superalloy DD6

The second generation single crystal superalloy DD6 with 0.10%Hf and 0.34%Hf (in mass fraction) was subjected to high-cycle fatigue (HCF) loading at temperatures of 700 °C in ambient atmosphere. SEM was used to determine the initiation site and the failure mechanism. Evolution of the microstructure was investigated by TEM observation. The results show that fatigue limit of DD6 alloy with 0.34%Hf is a little smaller than that of the alloy with 0.10%Hf. The fatigue cracks initiated on the surface or near the surface of the specimens. The crack would propagate along {111} octahedral slip planes, rather than perpendicular to the loading axis of specimen. Typical fatigue striation formed in steady propagation of fatigue crack. The fracture mechanisms of the high cycle fatigue of DD6 alloys with 0.10%Hf and 0.34%Hf are quasi-cleavage fracture. Different types of dislocation structures were developed during high cycle fatigue deformation.

Relevant Cubic Grain Plank Plastic Strain Ratio (R) the Theory Research and Experiment

This paper shows that different materials have different quadratic functions, tensor function theory can make the function of history to represent the plastic strain, which can be a sheet metal pressing does uniaxial tensile test show that the plane of sheet metal, sheet metal specimen axis and the angle between the rolling direction changes, to the metal plastic strain ratio (R) along with the changes. To explain this phenomenon, the introduction of a quadratic yield function to describe the experimental results of some of the metal sheet. This paper shows that different materials have different quadratic functions, tensor function theory can make the function of history to represent the plastic strain, which can be a sheet metal pressing does not depend on the value of history.

Microstructure and mechanical behaviour of Ti―6Al―7Nb alloy produced by selective laser melting

Abstract Selective laser melting (SLM) is an advanced manufacturing technology providing alternative method of producing complex components directly from 3D computer models. The purpose of this work is to determine the influence of the SLM manufacturing strategy on mechanical properties and microstructure of the as-built Ti―Al―Nb alloy. Specimens of Ti―6Al―7Nb were produced in three versions of the specimen axis orientation with respect to its build direction. Mechanical characteristics of the alloy were determined by tensile and compression testing, as well as hardness measurements. Microstructures were characterised utilising optical microscopy, scanning electron microscopy and X-ray diffraction analysis. It was found that the as-built Ti―6Al―7Nb alloy has microstructure of α′ martensite hardened by dispersive precipitates of the second phase, which results in higher tensile and compressive strengths, but lower ductility in comparison to those of an alloy manufactured by conventional methods. The layered microstructure of the material gives it a significant anisotropy of Young's modulus, moderate anisotropy of mechanical properties, but strong anisotropy of sensitivity to the build porosity. The paper develops understanding of the relationships between the strategy of layered manufacturing of the Ti―6Al―7Nb alloy and its microstructural and mechanical characteristics. This is important for future applications of the SLM technology for producing Ti―6Al―7Nb parts, e.g. the custom medical implants.

Experimental Study on the Relation between Elastic and Thermal Deformation of the AZ31 Magnesium Alloy and Composite

The dilatation characteristics of the continuosly cast AZ31 alloy and composite with AZ31 matrix reinforced by SiC nanoparticles were investigated in the temperature range of 20-410 °C. The axis of specimens was either parallel or perpendicular to the casting texture. The linear thermal expansion of the alloy as well as the composite was measured in an argon protective atmosphere using a Netzsch 410 dilatometer. The relative elongation and coefficient of thermal expansion are the main experimental results obtained using dilatometry. The temperature dependence of the elastic modulus can be calculated using analysis of the dilatometry results.

Multiaxial Low Cycle Fatigue Test Method for Cruciform Specimen of Nickel-Base Single Crystal Superalloy

This paper presented the multiaxial low cycle fatigue test method for cruciform specimens of YH61 nickel base single crystal superalloy . The elastic compliances were obtained in tensile and torsion tests using single crystal bar specimens whose specimen axis was aligned to the crystal growth directions of [100] and [110]. Elastic finite element analysis was performed to determine specimen shape and relationship between the specimen axis and crystal growth direction. Multiaxial low cycle fatigue tests were performed using the cruciform specimens whose x axis was aligned to the [001] direction and the y axis to [010], [110] and [210] directions both x and y axis were aligned to the<110> direction. Mises equivalent strain was not a suitable parameter and Mises equivalent stress was proved to be available for the correlating the multiaxial fatigue lives of the single crystal superalloy.

Lattice Plane Spacing Change in Hardened Layer of Chrome Molybdenum Steel after Carburizing and Quenching

Block specimens of chrome molybdenum steel with 0.20 mass% C, SCM420, were carburized in carrier gas and quenched in oil bath. The hardness and carbon content gradients in the hardened layer were measured experimentally. The carburized surface of one block specimen was gradually removed by electrolytic polishing. Ten thin plates were cut from the total case depth of the other block specimen. An experimental method to determine the stress-free lattice plane spacing of the hardened layer was examined using x-ray and neutron radiations. As a result, the stress-free lattice plane spacing change in the hardened layer could be determined successfully by measuring neutron diffraction peaks from Fe-211 of the thin plates during rotating ±90° around the specimen axis. Using x-ray, the stress-free lattice plane spacing at the carburized surface could be also determined by measuring the 2θ-sin2ψ diagrams of either removed surface of block specimen or thin plate. However, under the carburized surface, the Kα2 diffraction from the heat-treated eutectoid phase was superimposed on x-ray diffraction peak because the subsurface microstructure was composed of martensitic and heat-treated eutectoid phases. The stress-free lattice plane spacing under the carburized surface could not be determined using x-ray. Furthermore, the stress-free lattice plane spacing of Fe-211 was found to decrease with increasing the distance from the carburized surface and be expressed by the cubic function of the carbon content in the hardened layer.

The Increase in a Brittle-to-ductile Transition Temperature in Fe–Al Single Crystals

The effect of aluminium concentration on a brittle-to-ductile transition (BDT) has been investigated in Fe–Al single crystals. The BDT temperatures in Fe-4mass%Al and Fe-8mass%Al crystals with specimen axis were measured by an instrumental falling weight impact tester, indicating that the BDT temperature in Fe-8%Al is higher than that in Fe-4%Al. Twin-twin intersections were seen on fracture surfaces in Fe-8%Al tested at low temperatures, which shows that the intersection was the origin of a brittle fracture. In order to highlight the effect of deformation twinning on the BDT behaviour, specimens with the axis were also employed to suppress the onset of deformation twinning during the impact tests. The BDT temperature in Fe-8%Al was found to be decreased by suppressing deformation twinning, which indicates that deformation twinning is a key mechanism behind increasing the BDT temperature in Fe–Al single crystals. A model to explain the increase in the BDT temperature with aluminium content is also presented.

ALTERNATE PLIES AND ADHESIVE BONDS IN THE SPLITTING RESISTANCE OF PLYWOOD

Strengths of plywood subjected to in-plane tension, bending, and interior pressure in a hole were experimentally investigated. The tested plywood is composed of nine plies of lauan veneer, and the plies are bonded together with melamine-urea-formaldehyde cocondensate adhesives. These tests, when the axis of tensile or bending specimen is inclined to the face grain, reveal the reason why plywood is so resistant against splitting failure is owing to the alternate perpendicular plies of veneer as well as the sufficient shear strength of adhesive bond. In such a case, the crack of veneer is interrupted by neighborhood veneer, and then the fracture path is associated with shear failure of the bond. In other words, either tensile or bending strength of such an inclined plywood member is substantially elevated by the shear strength of the bond. For the same reason, the holed plate under interior pressure does not split but experiences compressive yielding only if the edge distance is greater than double the diameter of the hole.

Effect of Al and Al-Si diffusion coating on the low cycle fatigue behavior of Inconel 713LC

Cylindrical specimens of Inconel 713LC in untreated condition and surface treated with Al and Al-Si diffusion coating were cyclically strained under strain control at 800 ̊C in air. The structural and hardness characteristics of the hardened surface layer are presented. Cyclic hardening/softening curves, cyclic stress-strain curves, and fatigue life curves are obtained. The sections parallel to the specimen axis have been examined to study fatigue damage mechanisms. The effect of Al coating on stress response and fatigue life slightly differs from that of Al-Si coating.

OS04F090 Effect of Misalignment on Residual Stress in Carbon Steel Socket Welded Joint

Residual stress remarkably affects the fatigue strength of welded socket joint. In carbon and austenitic stainless steel the fatigue strength of socket welded joint is about half of base metal. This is caused by the residual stress at the root of socked weld. In this study the variation of residual stress distribution near the weld start and end points, effects of miss-alignment on the residual stress distribution and the principal strain and stress were examined using the neutron diffraction method. As a result, the effects of misalignment are negligibly small and the residual stress at the weld root is almost the same with that of normally welded joint. The deviations of principal axes from the specimen directions are not so much large and the principal stresses almost agree with those of specimen axes.

Twist Extrusion: Fundamentals and Applications

We present a study of the kinematics of Twist Extrusion (TE) and show that the mode of deformation in ТЕ is a simple shear. Unlike in Equal-Channel Angular Pressing (ECAP), there are two main shear layers perpendicular to the specimen axis. TE has a significant commercial potential due to the following physical effects: intensive grain refinement; homogenization and mixing; intensive powder consolidation. Donetsk Institute for Physics and Engineering created a TE Center to showcase the process and educate investors. Our experience with the center has shown that the most prospective directions are producing ultrafine-grained (UFG) alloys for medical and aircraft applications.

Does Texturing of UHMWPE Increase Strength and Toughness?: A Pilot Study

Crosslinked UHMWPE as a bearing surface in total joint arthroplasty has higher wear resistance than conventional UHMWPE but lower strength and toughness. To produce crosslinked UHMWPE with improved mechanical properties, the material can be treated before crosslinking by tension to induce molecular alignment (texture). We asked how (1) the microstructure of UHMWPE evolves when subjected to tension and (2) whether the new microstructure (texture) increases strength and toughness. We analyzed microstructure evolution of UHMWPE by small- and wide-angle xray scattering and scanning electron microscopy. We then developed a method to characterize the local strength and toughness of undeformed and textured UHMWPEs by means of nanoscratch tests along and perpendicular to the specimen axis. In three samples we determined the scratch characteristics in terms of deformation mode, coefficient of friction (μ), and viscoelastic recovery (r). Before the tensile process, the scratch behavior of UHMWPE was characterized by a μ ranging from 0.64 to 0.68, no cracking, and r ranging from 0.58 to 0.60. Microfibrillar morphologic features resulted from the tensile process. The new microstructure had an increased strength (r=0.78) and decreased toughness (cracking+μ=0.77) perpendicular to the fibril axis and decreased strength (r=0.53) and increased toughness (no cracking+μ=0.55) parallel to the fibril axis. Textured UHMWPE behaves like a fiber composite with high strength and toughness in well-defined directions. However, the effect of crosslinking on these specific properties is unknown and therefore it is important to verify that the properties are retained. If wear resistance of crosslinked-textured UHMWPE is at least as high as that of crosslinked UHMWPE, novel medical devices made of crosslinked-textured UHMWPE could be developed and clinically tested.

Low Cycle Fatigue Behavior of Cast Superalloy Inconel 713LC with Al Coating at 800 °C

Cylindrical specimens of Inconel 713LC in as-cast condition and with Al diffusion coating by the CVD technique were cyclically strained under total strain control at 800 °C. Hardening/softening curves, cyclic stress-strain curves, and fatigue life curves are obtained. The coating has a beneficial effect on the Manson-Coffin curve while the fatigue life is reduced in the Basquin representation. The stress response of the coated material is lower in comparison with the uncoated one. Sections parallel to the specimen axis have been examined to study fatigue damage mechanisms.