Mechanical Properties Of Structural Materials Research Articles

Mechanical Characterization of Electroplated Ni Films by Micro-tensile Testing

Mechanical properties of structural materials are particularly important for design,performance realization and reliability analysis of microelectromechanical systems (MEMS). Furthermore,accurate database of mechanical properties at the micro scale can provide indispensable reference for establishing MEMS standard. Electroplated nickel film is one of the most favored structural materials used in MEMS,thus its mechanical properties has been studied for many years. However,the measured values show large scatter in Young's modulus of nickel film. Young's modulus and yield stress of electroplated nickel film are measured by using a micro-tensile testing instrument. The tensile load applied on the specimen is measured by a load cell with accuracy 0.25 mN directly,without additional friction. Through measuring the axial stiffness coefficient of the tensile instrument in situ,the tensile strain of the specimen is obtained by using two-serial spring model. The electroplated nickel films were fabricated from sulfamate baths,and the gauge section is 500 μm long and 10 μm wide nominally,and thickness range between 25 μm and 50 μm. The obtained Young's modulus from tensile testing is 83±6 GPa for nickel specimens electroplated at current density of 20 mA/cm2 and it increases to 124±5 GPa as current density is decreased to 10 mA/cm2. The phenomena are interpreted in terms of porosity of microstructure. The higher current density produced microstucture with low density and high volume fraction of pores,and the microstructure of high porosity corresponds to a lower modulus. The measured values of Young's modulus are consistent with those of calculated from the exponential empirical formula between Young's modulus and porosity. The micro-tensile testing instrument can also be used for mechanical measurement of other MEMS films.

Investigation of the sensitivity to EAC of steel T91 in contact with liquid LBE

The ferritic–martensitic steel T91 is one of the most promising material for application in the generation IV type reactors. However, there are critical issues, such as the susceptibility to damage of the steel in contact with the heavy liquid metals and their effect on the mechanical properties of structural materials. In this context, it was initiated a study of the boundary conditions, necessary to ascertain the sensitivity of the T91 to environmentally assisted cracking when loaded in contact with the liquid lead–bismuth eutectic. A series of tensile tests were carried out in a cell where the specimens were immersed in static LBE. Results showed that at high temperature the steel in contact with the liquid metal had a slight decrease of yield and UTS value and a marked increase in the elongation to rupture. However, at low temperature the elongation to rupture and the reduction of area decreased, indicating the sensitivity to EAC.

Microstructure and mechanical properties of pearlitic gray cast iron

Mechanical properties of structural materials strongly depend on their microstructure. The aim of this work, which essentially has an experimental character, is to correlate microstructure and mechanical properties of pearlitic gray cast iron. Because of the industrial interest behind to this work, the material under study is extracted from identical sand-cast parts produced by three different foundries. Laboratory tests show that mechanical properties, as tensile and fatigue strength, of gray cast iron of the same grade vary from foundry to foundry. A noticeable statistical data scatter is found also, depending on the location of the castings from which the specimens are machined. The cause of this behaviour is ascribed to the inhomogeneity that characterizes the gray cast iron microstructure. Metallographic sections are observed to quantitatively measure the relevant microstructural parameters, as graphite lamellas morphology, eutectic cell size and inclusions content. Results are correlated to the measured mechanical properties: reduced graphite content increases the tensile and the fatigue strength, both fine eutectic cells structure and high eutectic phosphide percentage improve the fatigue properties.

Mechanical properties of structural materials from first-principles

First-principles method based on the electronic structure theory is one of the most promising approaches of computational materials design. Although only a few of mechanical properties (e.g., ideal strength and elastic constants) are accessible directly by first-principles calculations, such methods may predict the complex mechanical properties by extracting appropriate calculable parameters (e.g., the ratio of bulk modulus to shear modulus, the formation energies of and interaction energies between lattice defects) and adopting proper models (e.g., Peierls–Nabarro model for dislocation core). In this paper, we briefly review recent first-principles investigations of mechanical properties of structural materials, covering topics of ideal strength, elastic constants, and lattice defects. Some of the major recent advances, such as the application of coherent potential approximation coupled first-principles methods (accurate enough for the calculating of the elastic constants of random alloys with complex compositions), the appreciation of the importance of low C 11– C 12 to the ‘super properties’ of BCC-Ti based alloys, and the relationship between solute–vacancy interaction and creep resistance, etc., are highlighted.

Modeling of the Tritium Impact on Mechanical Properties of Structural Materials by Radiogenic Helium and Hydrogen Synergetic Effect Technique

The paper presents results of tritium-structural materials interaction modeling by simultaneous exposure to radiogenic helium-3 and hydrogen (both dissolved and external). This method of synergetic effect of radiogenic helium-3 and hydrogen is a radiation-safe technique to study the tritium impact on mechanical properties of structural materials. Applicability of the method is illustrated by technique and research results on the impact of high-pressure hydrogen (80MPa), helium-3 (concentration ~140appm) and their synergetic (hydrogen+3He) effects on mechanical properties of CrNi40MoCuTiAl alloy in temperature range from 20 to 600°C. It has been shown that joint effect of radiogenic helium-3 and hydrogen on mechanical properties of alloy can not be represented as the result of a simple summation of helium and hydrogen embrittlement. Proposed technique of synergetic impact of radiogenic helium-3 and hydrogen allows more correct simulation and investigation in the tritium impact on mechanical properties of materials than individual research in helium or hydrogen embrittlement.

Modeling of the Tritium Impact on Mechanical Properties of Structural Materials by Radiogenic Helium and Hydrogen Synergetic Effect Technique

Modeling of the Tritium Impact on Mechanical Properties of Structural Materials by Radiogenic Helium and Hydrogen Synergetic Effect Technique

Modelling of changes in physical and mechanical properties of structural materials during long-term exposures at elevated temperatures

Long-term exposures of various industrial structural materials at sufficiently elevated temperatures cause substantial changes in materials structures and, consequently, substantial changes in their physical and materials properties. The paper is focused to the influence of thermodegradation of glass-fibre-reinforced polyamide 66 in dry air and gear oil on its mechanical properties. As the thermodegradation of polymer materials is diffusion controlled process, the paper starts with the description of water diffusion in tested material. Then a very simple degradation mechanism is proposed for modelling the main features of real degradation processes. Regression functions describing the changes in mechanical properties of polyamide details during exposure are verified by the fit of experimental results. In the end of the paper some general considerations about the changes in other structural materials during exposures are done and supported by some experimental results.

Space Radiation Transport Properties of Polyethylene‐Based Composites

Composite materials that can serve as both effective shielding materials against cosmic-ray and energetic solar particles in deep space, as well as structural materials for habitat and spacecraft, remain a critical and mission enabling component in mission planning and exploration. Polyethylene is known to have excellent shielding properties due to its low density, coupled with high hydrogen content. Polyethylene-fiber reinforced composites promise to combine this shielding effectiveness with the required mechanical properties of structural materials. Samples of polyethylene-fiber reinforced epoxy matrix composite 1-5 cm thick were prepared at the NASA Marshall Space Flight Center and tested against a 500 MeV/nucleon Fe beam at the HIMAC facility of NIRS in Chiba, Japan. This paper presents measured and calculated results for the radiation transport properties of these samples.

Non-contact measurement of the mechanical properties of materials using an all-optical technique

Describes an optically-based measurement mechanism which realizes a totally noncontact assessment of the most important mechanical properties of structural materials - namely effective stiffness and Poisson ratio. These parameters are sensitive indicators of material integrity. The technique uses laser generated broadband ultrasound as a probe and interferometric optical detection as the detector again exploiting the broadband capability of optics in both space and time. Both detection and excitation systems are most conveniently realized in practical systems through optical fiber linkages. Observing the coupled waveforms between source and detector as a function of source: detector separation after a space : time Fourier transform yields a set of dispersion curves for the ultrasonic (typically Lamb wave) transfer function of the sample. This, in turn, can be inverted using curve fitting routines to obtain effective values of modulus and stiffness. An initial assessment of this inversion process is presented and demonstrates that the effective modulus can be extracted with a confidence level of better than a few percent with slightly larger errors in the Poisson ratio.

Experimental Methods and Mechanical Properties of Structural Materials Subjected to High-Rate Deformation 102 - 105 {roman s}-1 at Temperatures of 77–773 K

We describe basic methodical principles and the results of mechanical testing of structural materials under loads of various kinds at strain rates of up to 105 {roman s}-1 within the temperature range 77–773 K. It is shown that the strength of all investigated materials increases with the strain rate and this increase is especially pronounced at rates higher than 103 {roman s)-1. In this case, the plasticity of metals increase and the plasticity of polymers decreases. We propose a schematic description of the mechanical state of metals depending on the strain rate and temperature.

き裂発生・進展挙動の変動特性を基礎とした非鉄金属材料の確率疲労特性に関する研究

A large scale database MSDRD on mechanical properties of structural materials was constructed by the Research Group for Statistical Aspects of Materials Strength. In order to extract and analyze the material strength data from MSDRD, a software of STANAD was also developed by this research group. In the present study, fatigue data of aluminum alloys such as 2024-T4 and 5083BE-O were newly analyzed by the same software. Paying particular attention to the statistical feature of the crack initiation and propagation behaviors, statistical fatigue properties (P-S-N characteristics) were theoretically analyzed for smooth and notched specimens. Total fatigue life Nf is given by sum of the crack initiation life Ni and the crack propagation life Np. Thus we can derive the distribution function of Nf from the respective probability density functions of Ni and Np by applying the convolution integral. It was finally found that distribution characteristics of fatigue lives in a wide stress range were well explained by the present analytical model.

Helium and hydrogen induced hardening in 316LN stainless steel

In certain radiation environments, such as the spallation neutron source (SNS) presently in design and construction, the high transmutation production rate for helium and hydrogen, concomitant with displacement damage, may affect the mechanical properties of structural materials. To better understand this effect, we have studied type 316LN stainless steel specimens implanted with medium energy Fe-, He-, and H-ions, alone and in combination. In this report, we present nanoindentation measurements of the incremental increase in hardness caused by 360 keV He-ions implanted at 200°C to concentrations from 2 to 200 000 appm. The He-induced hardening was found to saturate at twice the level measured for Fe-induced displacement damage alone. The additional hardening at high helium concentrations was associated with the presence of helium filled cavities (bubbles), observed by transmission electron microscopy (TEM). We also found that co-injection of helium and hydrogen resulted in more hardening than was observed for He-implantation alone.

Effect of additional minor element on radiation-induced grain boundary segregation in austenitic stainless steel under electron irradiation

Radiation-induced segregation (RIS) influences the chemical and mechanical properties of structural materials of fission and fusion reactors. In the present study, we investigated the effect of minor alloying elements on RIS in austenitic stainless steel on the basis of the rate theory at or near grain boundaries. It was assumed that the additional minor elements interacted with vacancies and formed additive–vacancy complexes. The effects of additional element concentration and the binding energy between additives and vacancies on solute segregation at the grain boundary were clarified by the present calculations, and the results were compared with recent electron irradiation experiments using a high-voltage electron microscope (HVEM).

On stability of mechanical properties of deformed rods from powder molybdenum

The technology of powder metallurgy is widely used in the industry for the production of deformed semiproducts (rods, sheets, strips, forgings) from refractory metals, molybdenum (of grade M-PM) in particular. Molybdenum in the form of deformed rods is used in structures operating at a temperature of up to 2000°C. The requirements on the stability of the mechanical properties of structural materials are very strict (especially at room temperature). The stability of the mechanical properties of molybdenum rods is affected substantially by the types and conditions of the deformation treatment of the sintered preforms. The present work is devoted to the mechanical properties and parameters of rods from powder molybdenum obtained by extruding and rolling of sintered preforms with various degrees of deformation.

Determination of Tensile Properties at Increased Strain Rates and Various Temperatures

Abstract This paper reports on the development and first application of a low-cost dynamic tension testing method which makes testing at strain rates in the range of 100/s to 500/s and various temperatures as simple as an instrumented Charpy test. The kinematical and kinetic analysis of the newly introduced, reusable clamping device allows the determination of the stress-strain curve from the measured force history during the tearing process. The first results show that the new technique is very promising to determine the influence of loading rate and temperature on the mechanical properties of structural materials, since the measured dynamic tensile properties compare well in absolute value as well as accuracy and reproducibility with those obtained using conventional high-speed tension testing facilities.

Changes of mechanical properties of structural materials under radiation hydrogen saturation

Using accelerator techniques, the effect of radiation hydrogen saturation on mechanical and structural properties of 12Cr 20Mn 2W and 316 type stainless steels and vanadium alloys has been studied. A very clear effect of proton irradiation on the materials was observed at low temperatures and low initial plastic cold working levels. In conditions of high temperature irradiations, simulating hydrogen production and radiation displacements generation for fusion reactor, mechanical properties of the materials practically do not change.

A Creep Damage Estimation Method for In-Service Fossil Fuel Boiler Superheater Tubes

Abstract Because mechanical properties of structural materials for high-temperature use, such as boiler tubing, degrade during long-term service, it is essential to detect toughness degradation by means of a nondestructive and simple field test technique. A grain boundary etching technique is developed to detect material degradation, and assess creep strength and notch toughness. An etching test using a picric acid solution with a wetting agent or using 20 percent HNO3 with alcoholic solution was found to have great potential for the nondestructive estimation of grain boundary embrittlement caused by carbide and sigma precipitation in SUS stainless steel. The feasibility of this estimation procedure was determined showing the relationships between Charpy impact energy (CVN) and grooving width (WGS), and creep damage ratio (Φ) and WGS. Superheater tubes of fossil fuel boiler were tested on site to demonstrate the validity of this technique.

Energy-based method for determination of allowable stress—Part II

An energy-based method for determining allowable stresses, the main link in strength analysis, which for the first time takes account of a basic set of mechanical properties of structural materials, namely resources of plasticity, hardening (strain and low-temperature) and crack resistance, has been developed instead of the classical mechanical method involving the material strength characteristics only. By taking into account the basic mechanical properties, an increase in allowable stress according to the new method is achieved: from fractions of a percent for high-strength low-plasticity materials to 30% at room temperature and up to 50% at cryogenic temperatures for plastic hardening and nonembrittling materials and this allows reduced metal consumption in structures and machines without lowering the level of their reliability. Realization of the energy-based method for determining allowable stresses (calculated resistances) in the strength analysis opens up prospects of resolving the problem of making maximum use of actual strength for all steels and alloys used in machine building. This makes the method of great practical use.

Effects of radiation on the mechanical properties of structural materials

Effects of radiation on the mechanical properties of structural materials

A MODIFIED KOLSKY METHOD FOR THE INVESTIGATION OF THE STRAIN-RATE HISTORY DEPENDENCE OF MECHANICAL PROPERTIES OF MATERIALS

A fairly simple modification of the split Hopkinson bar (SHB) method is presented that extends significantly the scope of the Kolsky method in studying the effects of strain rate and strain-rate history on the physical and mechanical properties. The developed modification of the SHB method makes it possible to conduct incremental tests with alternating dynamic loading. Examples illustrating the possibilities of the modifications described are included. In the recent three decades the SHB method, originally proposed by H. Kolsky, has been successfully used all over the world to study strain-rate dependence of the mechanical properties of structural materials. Presently, this method is used to determine the mechanical properties of materials loaded in tension, compression, torsion and 3 — 1 shear CI] for the strain rates of 10 s . In some works this method was used to study the effects of strain-rate history on the mechanical properties of materials [2-63. Most results of this kind have been obtained in the experiments where a dynamic load was superposed on a previously applied static one. There is a number of works where dynamic shifts from one strain rate to another were accomplished during high-rate loading of the specimen C5-63. A Kolsky method modification that allowed to alternate the specimen loading and, thus, to study the dynamic Bauschinger effect was originally developed by Ogawa 171. Some simple modifications of the SHB method have been worked out by the present authors to extend its scope. To create complex strain-rate histories in specimens it is proposed to generate cyclic loads by loading the SHB system using projectiles made up of lengths of two or more bars of materials with different acoustic impedances pC, where p is material density and C is sound velocity in it. The bars the projectile is made up of may follow one another with no gaps between them C8.93 (glued together) or with some gaps CIO].