Quench Process and Steel Chemistry Optimization to Prevent Quench Cracking during Hardening of Splined Semi – Axles

In the paper the hardening process of splined semi-axles is discussed and physics of preventing the quench crack formation during intensive quenching (IQ) is explained. It is shown that during IQ process at the splined cylindrical surface very high compressive current band residual stresses are formed which prevent the possibility of quench crack formation on splines. It is enough to optimize the stress distribution through the section of semi-axle and perform IQ process in order to prevent quench cracks formation in splines. It is achieved via optimizing depth of surface hardened layer. In this case the depth of surface hardened layer for cylinders and for cylinders with splines are the same. There is no need to create a special thin shell on splines or perform carburization to create such shell. Due to larger martensite specific volume, it results in surface compressive residual stress formation. Absence of martensite phase at the core eliminates core swelling that could be a reason in tensile surface stresses. The idea is supported by FEM calculations and testing of real semi-axles in industrial condition. The new idea simplifies cardinally technological process and makes it less costly.

Strengthening of tensile zone of the reinforced concrete beams with composite fabrics

A fabric, tapes, that are glued to the outer tensile surface, which are considered as the external composite reinforcement with tensile steel reinforcement, are currently used to strengthen reinforced concrete beams. The results of the experimental studies presented in this article have shown the possibilities of effective application of technical polyamide (nylon) fabric produced by «Khimvolokno Plant» JSC «Grodno Azot», and glass fabrics, produced by JSC «Polotsk-Steklovolokno» for strengthening the reinforced concrete beams. Experimental studies have shown that the external reinforcing of the tensile zone with technical polyamide (nylon) fabric and fiberglass changes the beam failure mode, increases the bearing capacity of reinforced concrete beams in comparison with beams without strengthening by 16% – 38%, depending on the material and the method of strengthening.

Anomalous Elastic Properties of Attraction-Dominated DNA Self-Assembled 2D Films and the Resultant Dynamic Biodetection Signals of Microbeam Sensors

The condensation of DNA helices has been regularly found in cell nucleus, bacterial nucleoids, and viral capsids, and during its relevant biodetections the attractive interactions between DNA helices could not be neglected. In this letter, we theoretically characterize the elastic properties of double-stranded DNA (dsDNA) self-assembled 2D films and their multiscale correlations with the dynamic detection signals of DNA-microbeams. The comparison of attraction- and repulsion-dominated DNA films shows that the competition between attractive and repulsive micro-interactions endows dsDNA films in multivalent salt solutions with anomalous elastic properties such as tensile surface stresses and negative moduli; the occurrence of the tensile surface stress for the attraction-dominated DNA self-assembled film reveals the possible physical mechanism of the condensation found in organism. Furthermore, dynamic analyses of a hinged–hinged DNA-microbeam reveal non-monotonous frequency shifts due to attraction- or repulsion-dominated dsDNA adsorptions and dynamic instability occurrence during the detections of repulsion-dominated DNA films. This dynamic instability implies the existence of a sensitive interval of material parameters in which DNA adsorptions will induce a drastic natural frequency shift or a jump of vibration mode even with a tiny variation of the detection conditions. These new insights might provide us some potential guidance to achieve an ultra-highly sensitive biodetection method in the future.

Stress distribution and failure load of multilayer and monolayer glass ceramic.

This short report evaluated the differences in stress concentration and the load to fracture of multilayered and monolayer glass ceramic discs. Using a static structural analysis, the 3D model of the discs received a load of 150N and results in maximum principal stress were obtained. For the in vitro analysis, the samples (ø 12 mm) were submitted to a compressive test (100kgf, 1mm/min). The data was analyzed using one-way analysis of variance and Tukey test (α=5%). The monolayer group showed a lower stress peak (129.24 MPa) and higher load to fracture (118.38N) than the multilayered group with 211.04MPa and 48.34N, respectively. All samples presented catastrophic failure with its origin on the tensile surface. Therefore, the monolayer ceramic group showed superior mechanical behavior than the multilayered group.

Influence of the geometry of ceramic specimens on biaxial flexural strength: experimental testing and finite element analysis

This study evaluated the influence of the geometry of ceramic specimens (disc vs. square plate) on the biaxial flexural strength (BFS) using an experimental set and finite element analysis (FEA). Leucite glass-ceramic blocks were used in the preparation of disc (D; n=14) and square plate (S; n=13) specimens with the same lower (tensile) surface area. The specimens were subjected to a piston-on-three-ball flexural test (ISO 6872:2008). To calculate the BFS of the S group, the specimen radius, indicated by the ISO 6872:2008 formula for discs, was replaced by half of the side length. FEA compared the pattern of stress distribution and the first principal stress between D and S specimens having the same and different lower (tensile) surface area. Student’s t-test showed no difference (p=0.85) in the BFS between D (95.0±9.6 MPa) and S (84.3±10.3 MPa). FEA indicated a similar pattern of stress distribution, with almost no difference in the first principal stress of discs and square plates with the same lower (tensile) surface area. In the experimental condition investigated, square plate ceramic specimens can be used in piston-on-three-ball tests. For the calculation of the BFS, the specimen radius may be replaced by half side length of the square specimen.

LAND SUBSIDENCE DUE TO EXCESSIVE GROUND WATER WITHDRAWAL. A CASE STUDY FROM STAVROS - FARSALA SITE, WEST THESSALY GREECE

Land subsidence manifestation due to ground-water overexploitation in the Stavros – Farsala site (eastern part of Western Thessaly Basin) has been noticed since 1990. Because of this overexploitation, an excessive drawdown of the ground water level (20 to 40m) was noticed in the various successive aquifers the last decades. The subsidence phenomena resulted to the formation of tensile surface ruptures, which occurred since 2002, affecting roads and buildings. The geological environment of the study area consists of terrestrial Pleistocene deposits containing sands and gravels interbedded with clayey silt to silty clay horizons. These alternations of aquifers (permeable coarse-grained deposits) with aquitards (impermeable to low permeability strata) create a number of successive semi-confined to confined aquifer, initially artesian. This study examines the geological and the hydrogeological conditions of the wider study area, aiming to clarify their relationship with subsidence phenomena and to provide solutions for their suspension. Note that those phenomena are expected to be more incensed during the next few years.