Range Of Strain States Research Articles

Magnetism in CaMnO3 thin films

Epitaxial CaMnO3 thin films on (001) LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and SrTiO3 were synthesized in a range of strain states from coherently strained on LaAlO3 (1.6% strain) to fully relaxed on SrTiO3. We observed a magnetic ordering transition in CaMnO3 thin films suppressed from the Néel temperature of bulk CaMnO3 with the suppression increasing with increasing strain in the thin film. In contrast to bulk studies, our CaMnO3 films do not exhibit any sign of weak ferromagnetism according to field-dependent magnetization and x-ray magnetic circular dichroism measurements. Therefore, to within experimental resolution, all of our CaMnO3 films are antiferromagnetic with negligible oxygen off-stoichiometry.

Quantification of octahedral rotations in strained LaAlO3films via synchrotron x-ray diffraction

In recent years, there has been an increased interest in octahedral rotations in perovskite materials, particularly on their response to strain in epitaxial thin films. The current theoretical framework assumes that rotations are affected primarily through the change in in-plane lattice parameters imposed by coherent heteroepitaxy on a substrate of different lattice constant. This model, which permits prediction of the thin-film rotational pattern using first-principles density functional theory, has not been tested quantitatively over a range of strain states. To assess the validity of this picture, coherent LaAlO${}_{3}$ thin films were grown on SrTiO${}_{3}$, NdGaO${}_{3}$, LaSrAlO${}_{4}$, NdAlO${}_{3}$, and YAlO${}_{3}$ substrates to achieve strain states ranging from $+$3.03$%$ to $\ensuremath{-}$2.35$%$. The out-of-plane and in-plane octahedral rotation angles were extracted from the intensity of superlattice reflections measured using synchrotron x-ray diffraction. Density functional calculations show that no measurable change in intrinsic defect concentration should occur throughout the range of accessible strain states. Thus, the measured rotation angles were compared with those calculated previously for defect-free films. [Hatt and Spaldin, Phys. Rev. B 82, 195402 (2010)]. Good agreement between theory and experiment was found, suggesting that the current framework correctly captures the appropriate physics in LaAlO${}_{3}$.

Experimental and Numerical Analysis of Forming Limits in CNC Incremental Sheet Forming

Asymmetric incremental sheet forming (AISF) is a relatively new manufacturing process for the production of low volumes of sheet metal parts. Forming is accomplished by the CNC controlled movements of a simple ball-headed tool that follows a 3D trajectory to gradually shape the sheet metal blank. Due to the local plastic deformation under the tool, there is almost no draw-in from the flange region to avoid thinning in the forming zone. As a consequence, sheet thinning limits the amount of bearable deformation, and thus the range of possible applications. Much attention has been given to the maximum strains that can be attained in AISF. Several authors have found that the forming limits are considerably higher than those obtained using a Nakazima test and that the forming limit curve is approximately a straight line (mostly having a slope of -1) in the stretching region of the FLD. Based on these findings they conclude that the “conventional” forming limit curves cannot be used for AISF and propose dedicated tests to record forming limit diagrams for AISF. Up to now, there is no standardised test and no evaluation procedure for the determination of FLCs for AISF. In the present paper, we start with an analysis of the range of strain states and strain paths that are covered by the various tests that can be found in the literature. This is accomplished by means of on-line deformation measurements using a stereovision system. From these measurements, necking and fracture limits are derived. It is found that the fracture limits can be described consistently by a straight line with negative slope. The necking limits seem to be highly dependent on the test shapes and forming parameters. It is concluded that standardisation in both testing conditions and the evaluation procedures is necessary, and that a forming limit curve does not seem to be an appropriate tool to predict the feasibility of a given part design.

"Quartz-eye"-bearing porphyroidal rocks and volcanogenic massive sulfide deposits

This paper presents data supporting the conclusion that the combined association of (1) pyrite-rich stratigraphic units and (2) a characteristic style of quartz-eye porphyry is closely related to the occurrence of volcanogenic massive sulfide deposits.Textural observations on the quartz-eye porphyries suggest that the origin of this rock type may be more complex than that comprising simple metamorphism of a crystal tuff, acid flow, or intrusive rock type. Data are interpreted as suggesting that the quartz eyes are porphyroblastically overprinted on the schistose matrix of these rocks. Quartz eyes are also developed in wall rocks marginal to these quartz-eye porphyries.Because (1) the regional schistosity is steeply oriented and is related to a regional first phase of deformation, and (2) there is a range of strain states of the quartz eyes from highly deformed to undeformed within the same matrix, it is implied that these quartz eyes have grown in an actively deforming matrix and that the quartz-eye porphyries are metasomatically altered acid melts which were previously syntectonically intruded.In the genesis of massive volcanogenic sulfide deposits it is necessary to reconcile the complex origin of these porphyroidal rock types with that of the sedimentary origin of the pyritic units.