Magneto-Structural Relationship of Tetragonally-Compressed Octahedral Iron(II) Complex Surrounded by a pseudo-S6 Symmetric Hexakis-Dimethylsulfoxide Environment

Since the octahedral high-spin iron(II) complex has the 5T2g ground term, the spin-orbit coupling should be considered in magnetic analysis; however, such treatment is rarely seen in recent papers, although the symmetry-sensitive property is of interest to investigate in detail. A method to consider the T-term magnetism was well constructed more than half a century ago. On the other hand, the method has been still improved in recent years. In this study, the octahedral high-spin iron(II) complex [Fe(dmso)6][BPh4]2 (dmso: dimethylsulfoxide) was newly prepared, and the single-crystal X-ray diffraction method revealed the tetragonal compression of the D4-symmetric coordination geometry around the iron(II) ion and the pseudo-S6 hexakis-dmso environment. From the magnetic data, the sign of the axial splitting parameter, Δ, was found to be negative, indicating the 5E ground state in the D4 symmetry. The DFT computation showed the electronic configuration of (dxz)2(dx2−y2)1(dyz)1(dxy)1(dz2)1 due to the tetragonal compression and the pseudo-S6 environment of dmso π orbitals. The electronic configuration corresponded to the 5E ground term, which was in agreement with the negative Δ value. Therefore, the structurally predicted ground state was consistent with the estimation from the magnetic measurements.

Determination of Scale Effects on Mechanical Properties of Berea Sandstone

The key rock mechanical parameters are strength, elastic modulus, Poisson’s ratio, etc., which are important in reservoir development. The accurate determination of reservoir’s mechanical properties is critical to reduce drilling risk and maximize well productivity. Precisely estimating rock mechanical properties is important in drilling and well completion design, as well as crucial for hydraulic fracturing. Rocks are heterogeneous and anisotropic materials. The mechanical properties vary not only with rock types but also with measurement methods, sample geometric dimensions (sample length to diameter ratio and size), and other factors. To investigate sample scale effects on rock mechanical behaviors, unconfined compression tests were conducted on 41 different geometric dimensions of Berea sandstones; unconfined compressive strength (UCS), Young’s modulus ( E ), Poisson’s ratio ( υ ), bulk modulus ( K ), and shear modulus ( G ) were obtained and compared. The results indicate that sample geometry can significantly affect rock mechanical properties: (1) UCS decreases with the increase of length to diameter ratio (LDR), and the UCS standardize factor is between 0.71 and 1.17, which means -30% to +20% variation of UCS with LDR changing from 1 to 6.7. The test results show UCS exhibits positive relationship with sample size. (2) Young’s modulus slightly increases with LDR increases, while Poisson’s ratio decreases with the increase of LDR. For the tested Berea sandstones, Poisson’s ratio standardizing factor is between 0.57 and 1.11. (3) Bulk modulus of Berea sandstone samples decreases with the increase of LDR, while shear modulus increases with LDR increases. Both bulk modulus and shear modulus increase with the increase of sample size. (4) The principal failure modes were analyzed. The failure modes of the tested Berea sandstones are axial splitting and shear failure. Stocky samples ( LDR < 2 ) tend to go axial splitting, while slender samples ( LDR > 2 ) tend to show shear failure.

Analysis of the Damage Characteristics and Energy Dissipation of Rocks with a Vertical Hole under Cyclic Impact Loads

This study systematically investigates the failure patterns, energy dissipation, and fracture behavior of rock specimens containing a vertical hole under impact loads. First, an improved damage calculation equation suitable for the analysis of rock specimens with a vertical hole is obtained based on the one-dimensional stress wave theory and the interface continuity condition. After that, the Hopkinson pressure bar (SHPB) device was used to conduct cyclic impact tests with different impact pressures and impact modes (impact pressures with equal amplitude and unequal amplitude). The experimental results suggest that, under the equal-amplitude high pressure and unequal-amplitude pressure, the degree of damage of the rock significantly increased, the bearing capacity greatly reduced, and the rock gradually transitions from having good ductility to experiencing brittle failure. The cumulative specific energy absorption value gradually increases with the increase in the cyclic impact. Compared to that of the equal impact condition, the degree of damage to the rock is more severe for the case of equal-amplitude high pressure and unequal impact, and the failure mode undergoes a transformation from transverse tensile failure to transverse tensile failure-axial splitting failure combination and axial splitting failure. Through the analysis of rock energy changes and rock failure patterns during cyclic impact, it will be helpful to predict and control the fracture caused by local stress concentration during excavation, thus can reduce the cost of support and reinforcement in excavation and improve the stability of surrounding rocks.

Mechanical behavior of polyimide filament tows under high strain rate tension

The tensile properties of polyimide (PI) filament tows were measured under quasi-static state and at high strain rates with a universal tensile testing machine and a split Hopkinson tension bar, respectively. Experimental results showed that mechanical behaviors of the tows were rather sensitive to strain rate, with failure stress and modulus increasing distinctly but the elongation at break declining as the strain rate increased. Besides, the PI filament tows exhibited a higher growth rate of fracture stress than para-aramid fiber and aramid III fiber did, and scanning electronic microscopy observation on the fracture surface indicated a ductile fracture mode. With the increase of strain rate, the axial splitting of fiber intensified. Further, strength distributions of the PI filament tows were evaluated by a single Weibull distribution function, and the curve predicted was in good accordance with the experimental data obtained.

Experimental and Theoretical Investigation of Combined Expansion Tube-Axial Splitting as Impact Energy Absorbers

In this study, the combination of an expansion tube and a deformable rigid tube with axial splitting is developed as a new mechanism for use as an impact energy absorber. The impact absorbing structure consists of two circular tube forming dies, with each die allowing the tube to expand and to split. The latter is used to remove away radially the debris after expansion and splitting, so that the absorption process can continue without being obstructed by the debris itself. This paper presents the experimental and theoretical investigation of the combined expansion tube-axial splitting as an impact energy absorber. The experiment by the laboratory scale impact testing has been done with a variation of the parameters such as pipe thickness ([Formula: see text], angle of splitter ([Formula: see text], comparison of dies upgrading diameter ([Formula: see text] and inner pipe diameter ([Formula: see text] ([Formula: see text]/[Formula: see text]. The theoretical investigation is carried out with a literature study related to the mechanics of material and theoretical studies from previous research studies. The final result of this paper, i.e. a new formula proposed to calculate the mean load, is reflective of the study of a combined expansion tube with axial splitting. The difference between the results of analytical calculation and experiments is 10.13%.

Tensile properties of ultra-high-molecular-weight polyethylene single yarns at different strain rates

This paper presents the details of experimental work on characterising the tensile properties of UHMWPE (Spectra® 1000) single yarns at different strain rates from 3.3 × 10−5 to 400/s. According to the measured stress–strain curves, there was a transition from ductile to brittle behaviour as the strain rate increased from 3.3 × 10−5 to 0.33/s; the tensile properties were highly sensitive to strain rate in this range. Specifically, the tensile strength and Young’s modulus increased distinctly with increasing strain rate while the failure strain and toughness decreased. However, these tensile properties were not dependent on strain rate over the range from 0.33 to 400/s. The results showed that the measured tensile strength, failure strain and Young’s modulus were independent of the tested gauge lengths (25 and 50 mm). Moreover, yarn type (warp and weft) had a noticeable effect on tensile strength, but the effect of yarn type on failure strain and Young’s modulus was negligible. The microscopic examination of fractured fibres’ ends revealed that fibrillation and axial splitting were the dominant fracture modes at low strain rates, while the fibres failed in a more brittle manner with little fibrillation at high strain rates.

Experimental Study on Mechanical Properties, Failure Behavior and Energy Evolution of Different Coal-Rock Combined Specimens

To investigate the effect of the pure coal/rock strength on the mechanical behavior, failure behavior, and energy evolution of coal-rock combined (CRC) specimens, an AG-X250 Shimadzu Precision Universal Test was used to conduct uniaxial compressive loading, uniaxial cyclic loading, and unloading compression experiments on pure coal, pure rock, and different CRC specimens. The results show that the uniaxial compressive strength, Young’s modulus, and peak strain of the CRC specimen mainly depend on the coal specimen instead of the rock strength. The major failure modes of CRC were the shearing fracture and axial splitting failure, and for the CRC specimen with the same hard rock, the CRC specimen severely failed due to axial splitting cracks. In addition, the released elastic energy Ue, dissipated energy Ud, and kinetic energy Ur increase with increasing rock mass/coal strength, and for CRC specimen with the same coal, the greater the difference in strength between the rock and coal is, the greater the kinetic energy is.