Experimental Research on Rubber Compatibility of Drive Train oils used in Construction Machinery

The compatibility of oil and rubber in the drive train system of construction machinery plays an important role in the safe and reliable operation of the system. In order to investigate the rubber compatibility of drive train system oil of construction machinery, the changes of rubber sheet volume and hardness before and after immersion of standard fluororubber (FKM2) and hydrogenated nitrile rubber (HNBR1) with 9 kinds of drive train system oil were tested. The results show that FKM2 has good rubber compatibility with drive train oil, and HNBR1 is only compatible with some drive train oil; The volume change rate and hardness change range of FKM2 are smaller than those of HNBR1.

Effect of Surface Micro-Hardness Change in Multistep Machining on Friction and Wear Characteristics of Titanium Alloy

The machined surface quality, especially the micro-hardness of machined surface layers, is strongly correlated to the friction and wear characteristics of titanium alloy engineering parts. Therefore, to explore relationship of the local surface micro-hardness change in multistep machining and the surface wear resistance of the machined parts is urgently necessary. The machined surfaces were acquired through two-step (roughing and finishing) and three step (roughing, semi-finishing, and finishing) cylindrical turning experiments. The dry friction and wear tests were carried out by UMT-2 friction and wear tester on the multistep final machined surface along the feed direction. The surface wear microtopography and subsurface microstructure were observed and analyzed by scanning electron microscope. The micro-hardness variation in the local area of the finishing surface will cause the extension of unstable friction time stage while withstanding the cyclic and alternating contact stresses, and the soft–hard alternating area should be the sources of friction and wear defects, for instance cracks, peeling pits, fracture striations and even the wear fracture zone to crack propagation and peeling off. This will be of great significance to accurately control the machined surface quality and adaptively improve the surface wear resistance of titanium alloy components.

The Impact of Artificial Aging on the Color Stability and Hardness of Nanocomposite Resin

Objective: This study aimed to investigate the impact of artificial aging on the color stability and hardness of nanocomposite resin.Methods: Four nanocomposite resin materials were used: Filtek Z350 XT (FZ), Synergy D6 (SD), Grandio (GD), and Clearfil Majesty Esthetic (CM). Thirty specimens were created from each material, which were divided into three (A,B,C) groups of 10 specimens each. For each material, the values of visual lightness (L*), degree of redness and greenness (a*), and degree of yellowness and blueness (b*) of the specimens in group A before and after aging, as well as the hardness of the specimens in group B before aging and in group C after aging, were measured. The American Society for Testing and Materials (ASTM) G155 Cycle 1 standard was adopted to test the aging of the specimens. The color difference (ΔE00) value and hardness difference (ΔH) value of the specimens before and after aging were calculated.Results: Aging was found to have an impact on the ΔE00 values of the resin materials in each group (H = 17.6, p = 0.001), and the hardness of the specimens in each group after artificial aging was significantly higher than before aging (p < 0.05). The difference in ΔE00 between the FZ group and the SD, GD, and CM groups was statistically significant (p < 0.05). The FZ group had the highest ΔE00 values. There was no correlation between ΔE00 and the hardness change percentage after aging (r = 0.114).Conclusion: Among the four nanocomposite resins tested in this study, except for Filtek Z350 XT’s ΔE00 values (>1.8) in the clinically unacceptable range, the remaining three kinds of resin ΔE00 values (<1.8) were all in the clinically acceptable range. The hardness of the four nanocomposite resins increased after aging. The results of the present study revealed that there was no correlation between ΔE00 and hardness change percentage in the four nanocomposite resin materials after aging.

Evaluation of Hardness and Residual Stress Changes of AISI 4140 Steel Due to Thermal Load during Surface Grinding

During surface grinding, internal material loads are generated, which take effect on the surface and subsurface zone of AISI 4140 steel. High thermal loads can result in specific material modifications, e.g., hardness reduction and tensile residual stresses, due to inappropriate combinations of system and process parameters which influence the functional performance of the ground component in a negative way. In order to avoid this damaging impact due to the thermal effect, an in-depth understanding of the thermal loads and the resulting modifications is required. This relationship is described in the concept of Process Signatures applied in this paper. Experimentally determined temperature-time histories at various depths below the surface were used to estimate the thermal loads at the surface and subsurface using a numerical approach based on the finite element method (FEM). The results show that the hardness change during surface grinding correlates with the maximum temperature rate at given maximum temperatures. In addition, correlations between the hardness change and the Hollomon–Jaffe parameter are identified, taking into account both the absolute temperature and its evolution over time. Furthermore, it was shown that the surface residual stresses correlate with the maximum local temperature gradients at the surface if no detectable tempering of the microstructure takes place.

Crystallization and Hardness Change of the Ti-Based Bulk Metallic Glass Manufactured by a Laser Powder Bed Fusion Process

Ti-2.5Zr-5.0Hf-37.5Cu-7.5Ni-1.0Si-5.0Sn (at.%) BMG has been successfully manufactured in amorphous powder with a size of about 25 μm (D50). Using this amorphous powder, a Ti-based BMG was manufactured by an additive manufacturing process based on a laser powder bed fusion (LPBF) technique. In 3D printing processes using amorphous powders, it is necessary and important to understand the crystallization behavior due to the difference in energy density applied to the powders. An LPBF process has been carried out with various energy density conditions to minimize the inner defects and identify the sound mechanical properties of 3D-printed BMG parts. At the lowest energy density condition (3.0 J/mm3), the most pores were generated. Even if the same energy density (3.0 J/mm3) was applied, the rapid laser movement caused many pores to form inside the material. The relatively sound 3D-printed Ti-based BMG was successfully fabricated with a size of about 5 mm × 5 mm × 3 mm. Peaks at 41° and 44° showing crystallization were observed in all conditions. The higher the laser power was, the greater each peak intensity and the more crystallization (CuTi, Ti3Cu4, etc.) was present in the BMG, and the higher the scan speed, the more the internal defects were found.

Sandwich compression of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa) wood: density distribution, surface hardness and their controllability

The sapwood and heartwood of plantation sugi wood (Cryptomeria japonica), and plantation hinoki (Chamaecyparis obtusa) wood were flat-sawn into timbers, then kiln-dried to a MC level below 12%. These timbers were further processed into specific sizes and wetted on the surfaces, preheated at 150 °C and radially compressed into sandwich compressed timbers. Density distribution, compressed layer(s) position and thickness, surface hardness were investigated. It was demonstrated that sugi and hinoki timbers were both applicable for sandwich compression. By controlling the preheating time, sugi heartwood timber, sugi sapwood timber and hinoki timber can be all sandwich compressed, which resulted in surfaces compressed timbers, interior compressed timbers and center compressed timbers. When sugi timbers were sandwich compressed, density only tremendously increased in the earlywood. The increased density of the compressed sugi earlywood was independent of compressed layer(s) position, compressing distance or annual growth width, while for hinoki timbers compression, density increased both in earlywood and latewood. Surface hardness of the uncompressed sugi sapwood was almost twice of that of the uncompressed sugi heartwood. Surface compression sharply increased the surface hardness of sugi heartwood and sugi sapwood. Interior compression and center compression also contributed to increased surface hardness for the compressed timbers, but to smaller extents. Surface hardness change due to the surface compression was consistent with the surface average density change of timbers. Compression layer(s) position exerted statistically significant effects on the surface hardness, while surface hardness of the compressed wood was almost unrelated to the original density of the used wood or average density of the sandwich compressed wood. However, bigger compressing distance led to bigger surface hardness for the surface compressed wood.

Finite element modelling of microstructural changes during equal channel angular drawing of pure aluminium

Grain refinement by severe plastic deformation (SPD) techniques, as a mechanism to control microstructure (recrystallization, grain size changes,…) and mechanical properties (yield strength, ultimate tensile strength, strain, hardness variation…) of pure aluminium conductor wires, is a topic of great interest for both academic and industrial research activities. This paper presents an innovative finite element (FE) model able to describe the microstructural evolution and the continuous dynamic recrystallization (CDRX) that occur during equal channel angular drawing (ECAD) of commercial 1370 pure aluminium (99.7% Al). A user subroutine has been developed based on the continuum mechanical model and the Hall-Petch (H-P) equations to predict grain size variation and hardness change. The model is validated by comparison with the experimental results and a predictive analysis is conducted varying the channel die angles. The study provides an accurate prediction of both the thermo-mechanical and the microstructural phenomena that occur during the process characterized by large plastic deformation.

Finite Element Modeling of Microstructural Changes During Equal Channel Angular Drawing of Pure Aluminium

Grain refinement by severe plastic deformation (SPD) techniques, as a mechanism to control microstructure (recrystallization, grain size changes,…) and mechanical properties (yield strength, ultimate tensile strength, strain, hardness variation…) of pure aluminium conductor wires, is a topic of great interest for both academic and industrial research activities. This paper presents an innovative finite element (FE) model able to describe the microstructural evolution and the continuous dynamic recrystallization (CDRX) that occur during equal channel angular drawing (ECAD) of commercial 1370 pure aluminium (99.7% Al). A user subroutine has been developed based on the continuum mechanical model and the Hall-Petch (H-P) equations to predict grain size variation and hardness change. The model is validated by comparison with the experimental results and a predictive analysis is conducted varying the channel die angles. The study provides an accurate prediction of both the thermo-mechanical and the microstructural phenomena that occur during the process characterised by large plastic deformation.

LF NMR spectroscopy analysis of water dynamics and texture of Gluten-Free bread with cricket powder during storage

The paper presents the effect of replacing starch (at 2%, 6% and 10%) with cricket powder (CP) on the water behavior studied by the 1H NMR method, as well as the texture of gluten-free bread during 6-day storage. It was noticed that the bread crumb containing CP has lower water transport rate than the control bread crumb, while concluding that 2% CP stabilizes water transport throughout the entire staling time range. The NMR analyzes showed that the initial T21 values are the higher, the more starch has been replaced with the CP, however, after 6 days of storage, all tested samples are characterized by similar values of the T21 parameter. A decrease in long component of spin-spin relaxation time T22 during storage was also observed. It has been noted that the replacement of starch to 2% and 6% CP causes an increase in the molecular dynamics of water. The less starch present, the greater the potential for bulk molecules to move. The observed changes at the molecular level resulted in macroscopic changes in the texture of the bread. After analyzing the hardness parameter of the tested breads, it was found that on the day of baking, bread without the addition of CP had significantly higher values of this parameter than breads with CP. For the sample without CP, the highest increase in total hardness change (123.93%) was noted during storage, which indicates the fastest texture change process. Based on the results obtained, it can be concluded that the use of cricket powder to enrich gluten-free bread can not only improve the nutritional value, but also effectively delay the process of bread staling.

Experimental study on aging performance of elevator polyurethane buffer

In this paper, the hygrothermal aging experiments of polyurethane buffer materials for elevator were carried out for 5 days, 10 days, 15 days, 20 days, 25 days and 33 days. The quality change, hardness change, tensile strength and elongation at break of the test materials before and after the experiment were compared and analyzed. The results show that the aging process of polyurethane materials is accelerated by the humid and hot environment.