The modulus of elasticity of steel - is it 200 GPa?

In cold-formed steel construction, the use of a range of thin, high strength steels (0.35 mm thickness and 550 MPa yield stress) has increased significantly in recent times. A good knowledge of the basic mechanical properties of these steels is needed for a satisfactory use of them. In relation to the modulus of elasticity, the current practice is to assume it to be about 200 GPa for all steel grades. However, tensile tests of these steels have consistently shown that the modulus of elasticity varies with grade of steel and thickness. It was found that it increases to values as high as 240 GPa for smaller thicknesses and higher grades of steel. This paper discusses this topic, presents the tensile test results for a number of steel grades and thicknesses, and attempts to develop a relationship between modulus of elasticity, yield stress and thickness for the steel grades considered in this investigation.

High pressure clamp for electrical measurements up to 8 GPa and temperature down to 77 K

A compact clamp-type high pressure cell for carrying out electrical conductivity measurements on small solid samples of size 1 mm or less at pressures upto 8 GPa (i.e., 80 kbar) and for use down to 77 K has been designed and fabricated. The pressure generated in the sample region has been calibrated at room temperature against the polymorphic phase transitions of Bismuth and Ytterbium. The pressure relaxation of the clamp at low temperatures has been estimated by monitoring the electrical conductivity behavior of lead. Review of Scientific Instruments is copyrighted by The American Institute of Physics.

Raman study of pressure-induced structural transitions in CsIO4 to 12 GPa

High pressure Raman scattering studies have been carried out on cesium periodate (CsIO4) using the diamond anvil cell. Three pressure-induced phase transitions occur in the range 0.1�12 GPa as indicated by abrupt changes in the Raman spectra, and pressure dependence of the phonon frequencies. The transitions are observed at 1.5, 4.5 and 6.2 GPa in the increasing pressure cycle. A large hysteresis is noticed for the reverse transition when releasing the pressure. The high pressure phase is nearly quenchable to ambient pressure. The nature of the pressure-induced transitions are discussed in terms of the sequence of pressure-induced transitions expected for scheelite-pseudoscheelite structure ABO4 compounds from crystal chemical considerations. For the softening of the two high frequency internal modes, a pressure-induced electronic change involving the 5 d states of cesium and 5 p states of iodine is invoked.

High-pressure synchrotron x-ray diffraction study of RMnO3 (R=Eu, Gd, Tb and Dy) upto 50 GPa

We have carried out synchrotron based high-pressure x-ray diffraction study of orthorhombic EuMnO3, GdMnO3, TbMnO3 and DyMnO3 up to 54.4, 41.6, 47.0 and 50.2 GPa, respectively. The diffraction peaks of all the four manganites shift monotonically to higher diffraction angles and the crystals retain the orthorhombic structure till the highest pressure. We have fitted the observed volume versus pressure data with the Birch-Murnaghan equation of state and determined the bulk modulus to be 185 +/- 6 GPa, 190 +/- 16 GPa, 188 +/- 9 GPa and 192 +/- 8 GPa for EuMnO3, GdMnO3, TbMnO3 and DyMnO3, respectively. The bulk modulus of EuMnO3 is comparable to other manganites, in contrast to theoretical predictions.

Pressure-induced phase transition in Bi2Se3 at 3 GPa: electronic topological transition or not?

In recent years, a low pressure transition around P similar to 3 GPa exhibited by the A(2)B(3)-type 3D topological insulators is attributed to an electronic topological transition (ETT) for which there is no direct evidence either from theory or experiments. We address this phase transition and other transitions at higher pressure in bismuth selenide (Bi2Se3) using Raman spectroscopy at pressure up to 26.2 GPa. We see clear Raman signatures of an isostructural phase transition at P similar to 2.4 GPa followed by structural transitions at similar to 10 GPa and 16 GPa. First-principles calculations reveal anomalously sharp changes in the structural parameters like the internal angle of the rhombohedral unit cell with a minimum in the c/a ratio near P similar to 3 GPa. While our calculations reveal the associated anomalies in vibrational frequencies and electronic bandgap, the calculated Z(2) invariant and Dirac conical surface electronic structure remain unchanged, showing that there is no change in the electronic topology at the lowest pressure transition.

2.0 GPa 块状斜长角闪岩部分熔融——时间和温度的影响

利用多顶砧压机,以青藏高原北喜马拉雅构造带的天然斜长角闪岩为样品,在2.0GPa,800~1000℃条件下进行了两个系列的块状样品脱水部分熔融实验:(1)保持压力p=2.0GPa,加热时间t=12h不变,改变温度(800℃~1000℃)的实验;(2)保持压力p=2.0GPa,温度T=850℃不变,改变加热时间(12~200h)的实验.结果表明,2.0GPa,加热12h的条件下,随温度升高,斜长角闪岩中依次生成了石榴石、熔体和单斜辉石,熔体的成分呈英云闪长质-花岗闪长质-英云闪长质的演化趋势.2.0GPa,850℃条件下,随加热时间增加,斜长角闪岩中依次生成了石榴石、熔体和单斜辉石,熔体的成分由英云闪长质向花岗闪长质演化.当块状岩石样品中熔体体积百分比的含量达到5%时,熔体已经相互连通.温度大于850℃的条件下生成的熔体其粘度在104Pas量级,已经满足了在地质时间尺度上熔体分凝形成岩浆的粘度要求.因此,可以认为在增厚地壳的下部,斜长角闪岩的脱水部分熔融可以形成英云闪长质-花岗质岩浆.

0.7～1.8 GPa,室温～1120℃条件下α-β石英相变的弹性参数

为了解高温高压条件下,α-β石英相变过程中的弹性性质,在0.7～1.8GPa,室温～1120℃条件下,利用多顶砧波速测量装置,采用脉冲反射-透射法,测量了α石英以及相变为β石英的纵波速度,弹性纵波穿过单晶α石英的方向为平行结晶轴X方向。实验结果表明,随温度升高,α石英的纵波速度开始非线性降低,之后,快速升高,这一现象是由于α-β石英相变引起的,依据晶体对称性与弹性参数的关系确定了α石英的弹性参数(C_(11)),及其随温度和压力的变化关系,同时获得了β石英的弹性参数(C_(11)),实验证实,测量α-β石英相变时的纵波速度,不仅是确定α-β石英相变温度和压力的一种方法,也是校正高压腔体温度和压力的有力手段.

Investigation of the solid-liquid phase transition of carbon at 150 GPa with spectrally resolved X-ray scattering

We have resolved the solid-liquid phase transition of carbon at pressures around 150GPa. High-pressure samples of different temperatures were created by laser-driven shock compression of graphite and varying the initial density from 1.30g/cm³ to 2.25g/cm³. In this way, temperatures from 5700K to 14,500K could be achieved for relatively constant pressure according to hydrodynamic simulations. From measuring the elastic X-ray scattering intensity of vanadium K-alpha radiation at 4.95keVat a scattering angle of 126°, which is very sensitive to the solid-liquid transition, we can determine whether the sample had transitioned to the fluid phase. We find that samples of initial density 1.3g/cm³ and 1.85g/cm³ are liquid in the compressed states, whereas samples close to the ideal graphite crystal density of 2.25g/cm³ remain solid, probably in a diamond-like state.

Melting of metasomatized peridotite at 4–6 GPa and up to 1200 °C: an experimental approach

The phase assemblages and compositions in a K-bearing lherzolite + H2O system are determined between 4 and 6 GPa and 850–1200 °C, and the melting reactions occurring at subarc depth in subduction zones are constrained. Experiments were performed on a rocking multi-anvil apparatus. The experiments had around 16 wt% water content, and hydrous melt or aqueous fluid was segregated and trapped in a diamond aggregate layer. The compositions of the aqueous fluid and hydrous melt phases were measured using the cryogenic LA-ICP-MS technique. The residual lherzolite consists of olivine, orthopyroxene, clinopyroxene, and garnet, while diamond (C) is assumed to be inert. Hydrous and alkali-rich minerals were absent from the run products due to preferred dissolution of K2O (and Na2O) to the aqueous fluid/hydrous melt phases. The role of phlogopite in melting relations is, thus, controlled by the water content in the system: at the water content of around 16 wt% used here, phlogopite is unstable and thus does not participate in melting reactions. The water-saturated solidus, i.e., the first appearance of hydrous melt in the K–lherzolite composition, is located between 900 and 1000 °C at 4 GPa and between 1000 and 1100 °C at 5 and 6 GPa. Compositional jumps between hydrous melt and aqueous fluid at the solidus include a significant increase in the total dissolved solids load. All melts/fluids are peralkaline and calcium-rich. The melting reactions at the solidus are peritectic, as olivine, clinopyroxene, garnet, and H2O are consumed to generate hydrous melt plus orthopyroxene. Our fluid/melt compositional data demonstrate that the water-saturated hybrid peridotite solidus lies above 1000 °C at depths greater than 150 km and that the second critical endpoint is not reached at 6 GPa for a K2O–Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–Cr2O3(–TiO2) peridotite composition.