Papers by Keyword: Deformation Behavior

Abstract: This study examines the influence of the structural type of bitumen and its consistency on deformation behavior under low-temperature conditions, focusing on the glass transition temperature range, which is critical for the design of frost-resistant asphalt pavements. Motivated by the challenge of low-temperature cracking – a primary cause of asphalt pavement deterioration in cold climates – the research addresses the need to enhance bitumen’s stress relaxation capabilities to mitigate thermal cracking and extend pavement lifespan. Bitumen samples of gel, sol, and sol-gel structural types with different penetration grades (35/50, 100/150, and 160/220) were tested for creep compliance under axial tension at temperatures from -40 °C to 0 °C. The results showed that gel-type bitumen exhibit significantly higher creep compliance compared to sol-type bitumen with the same penetration, indicating better deformability. Specifically, gel-type bitumen demonstrated a plasticity index (m-value) 1.5–1.7 times higher than sol-type bitumen in the range from -40 °C to -30 °C, reflecting enhanced stress relaxation. The glass transition temperature of gel-type bitumen was found to be 4–6 °C lower than that of sol-type bitumen, further supporting its suitability for cold climates. These findings provide quantitative insights into optimizing bitumen selection for frost-resistant pavements, offering a creep compliance testing method that is simpler than traditional BBR and DSR approaches. The results are significant for improving pavement durability in regions with extreme temperature fluctuations, reducing maintenance costs, and guiding the development of performance-graded bitumen specifications.

Abstract: A material testing apparatus for measuring the biaxial deformation behavior of a polymer tube has been developed to quantitatively evaluate the deformation behavior of polymeric materials. The testing apparatus can apply axial force and internal pressure to a tubular specimen. A noncontact strain measurement system was also developed, and the biaxial strain components and the radius of curvature in the axial direction of the bulging specimen are continuously measured to control the stress path applied to the specimen. Polyethylene tube with an outer diameter of 17 mm and a thickness of 2 mm are used as a test sample. The tubular specimens were subjected to linear stress paths with stress ratios of σ_Φ:σ_θ =1:0, 4:1, 2:1, 4:3, 1:1, 3:4, 1:2, 1:4, and 0:1, where σ_Φ and σ_θ are the axial and circumferential stress components, respectively, applied to the central area of the bulging specimen. Loading and unloading tests were performed to determine the biaxial true stress-logarithmic plastic strain curves. The strain rate was 1×10^-3s^-1. From these test results, contours of plastic work and the directions of the plastic strain rates were measured to identify a proper material model for the test sample using the Yld2000-2d yield function (Barlat et al., 2003).

Abstract: Semi-solid processing combines the advantages of traditional forging and casting methods, so it has received much attention recently. However, the research on semi-solid behaviors of Nickel-based superalloys has been rarely reported. In order to investigate the behaviors of Nickel-based superalloy at solid and semi-solid states, oxidation experiments, isothermal treatment experiments and deformation experiments of GH4037 alloy were studied. Short-term oxidation experiments of GH4037 alloy were carried out at a solid temperature (1200 °C) and a semi-solid temperature (1360 °C). The results indicated that the oxides formed at 1200 °C were mainly composed of TiO₂, Cr₂O₃ and a small amount of spinels NiCr₂O₄, while the oxides formed at 1360 °C consisted of the spinels of NiCr₂O₄, NiWO₄ and NiMoO₄ besides TiO₂ and Cr₂O₃. Microstructure evolution of GH4037 alloy after semi-solid isothermal treatment at 1370 °C and 1380 °C was studied. The results indicated that semi-solid microstructures consisted of equiaxed solid grains and liquid phases. The average grains size and shape factor of solid grains were affected by melting mechanism and grain growth mechanism. Compression behaviors of GH4037 alloy after compressed at 1200 °C and 1360 °C were investigated. The results indicated that the flow stress of 1360 °C decreased significantly compared to that of 1200 °C. The deformation zones in the specimens were divided into three parts: the difficult deformation zone, the large deformation zone, and the free deformation zone. At 1200 °C, the deformation mechanism was plastic deformation mechanism. At 1360 °C, sliding between solid particles (SS), liquid flow (LF), flow of liquid incorporating solid particles (FLS), plastic deformation of solid particles (PDS) coexisted in the compression specimen.

Abstract: The uniform aluminum matrix syntactic foams (SFs) were prepared by the stir casting method, with alumina hollow spheres (2-3 mm and 3-4 mm) and expanded glass (2-3 mm) as reinforcements, and ZL111 aluminum alloy as matrix. The functionally graded aluminum matrix syntactic foams (FG-SFs) were obtained by superimposing two uniform aluminum matrix syntactic foams. Quasi-static compression tests were performed. The plateau stress of FG-SFs containing only hollow spheres decreased slightly with increasing volume fraction of SF containing 3-4 mm hollow spheres. The FG-SFs containing 2-3 mm hollow spheres and 2-3 mm expanded glass showed the highest plateau stress. The energy absorption behavior of all samples fluctuated in a small range. The initial position of shear band depended on the volume fraction of uniform aluminum matrix syntactic foams, reinforcement type and size. The cracks always appeared first in the uniform aluminum matrix syntactic foams containing expanded glass.

Abstract: Hot and cold deformation behavious and microstructure evolutions of Mn18Cr18N were investigated by thermo-mechanical modeling experiments and microstructure analysis. The results show that hot deformation flow stress curves characterized by the same work hardening and subsequent stress softening varied with temperatures and strain rates for both of as-cast and as-forged samples. And flow stresses are sensitive to strain rate. At strain rates lower than 0.01s^-1, the flow stresses are lower, and microstructure evolution controlled by dislocation mechanism dynamic recrystallization; At strain rates higher than 0.1s^-1, the flow stresses are higher, and microstructure evolution controlled by twinning mechanism dynamic recrystallization. But the dynamic recrystallzed fraction of the as-cast sample was much less than that of the as-forged sample. For cold deformation, the simple uniaxial tensile sample shows that the monotone increasing flow stress curve and monotone decreasing work-hanrdening rate. However, for the uniaxial and biaxial compression-tensile samples with different previous compression, the subsequent tensile yield stress, the maximum tensile stress, the reduction of cross sectional area and the elongation have extremums respectively at the previous compressive deformation of about 25%-30%. Microstructure evolution mechanisms during cold deformation were planar slipping and twinning.

Abstract: Under the current conditions, the consumption of special purpose alloys or steels is growing. This is due to the development of the import substitution program. It should be noted, that such materials possess specific deformation behavior, which requires providing particular conditions of a hot rolling process. One of the characteristics of the deformation behavior is the narrow thermal plastic range. Therefore, it is necessary to conduct a hot rolling in several stages, which include interchange of heating and rolling processes. For the purpose to resolve the issue, the experience of the multilayer hot rolling of plates has been investigated where all advantages of this way of a hot rolling process were used. Based on the method of the multilayer hot rolling, the pack rolling has been developed which gives the possibility of production of hot-rolled plates from special purpose alloys or steels.

Abstract: The deformation characteristics of Ti-5Al-5Mo-5V-1Fe-1Cr alloy during isothermal compression are investigated in this work. The alloy ingot is prepared by vacuum consumable furnace first. Then, thermomechanical processing and heat treatment are carried out. The microstructure shows the characteristics of Widmanstatten structure after heat treatment. The heat-treated material is subjected to isothermal compression test. According to the comparison of the coarsening degree of α grain under different experimental parameters. It is revealed that the strain rate has the largest influence on the stress field of the alloy during isothermal deformation.

Abstract: The mechanical properties of Fe-28%Mn-1.5%Al and Fe-0.6%C-18%Mn-1.5%Al-0.07%Nb (all in wt.%) steels subjected to hot plate rolling at a temperature of 1423 K with a total reduction of 60% were studied. The steels exhibited quite different mechanical properties in spite of almost the same original microstructures and similar stacking fault energies. The yield strength and total elongation of the Fe-28%Mn-1.5%Al steel are about 260 MPa and 45%, respectively, whereas those properties in the Fe-0.6%C-18%Mn-1.5%Al-0.07%Nb steel comprise 350 MPa and 53%, respectively. The tensile flow stress vs strain curves of the hot rolled steel samples can be described by Ludwigson-type relations with parameters being dependent on the strengthening mechanisms. Frequent deformation twinning in the Fe-0.6%C-18%Mn-1.5%Al-0.07%Nb steel promoted the strain hardening and improved the strength and ductility.

Abstract: In this study, to clarify the effects of Mo addition on deformation behavior of Ti-Mn alloys, the mechanical properties and the deformation structures of the alloys were investigated using Ti-Mn and Ti-Mn-Mo alloys polycrystals and single crystals. We found that the elongation of Ti-Mn alloys are improved from approximately 5% to 30% by Mo addition, with maintaining ultimate tensile strength of 900 MPa. The excellent strength-ductility balance of Ti-Mn-Mo alloys is caused by {332}<113> twinning, which is unique twinning for metastable β-type titanium alloys. Additionally, the deformation behavior of Ti-Mn and Ti-Mn-Mo alloys was investigated in detail by using single crystals focusing on a critical resolved shear stress (CRSS). As a result, we found for the first time that CRSS for {332}<113> twinning in Ti-Mn-Mo alloy was lower than that in Ti-Mn alloy. Moreover, in Ti-Mn-Mo alloy, CRSS for {332}<113> twinning was lower than that for {112}<111> slip. These results suggest that CRSS for {332}<113> twinning in Ti-Mn alloys is decreased by Mo addition.

Abstract: Alumina ceramics sintered at 1350, 1450 and 1550 °C with different grain sizes were tested under dynamic load using a small-scale compressed air gun with sharpened tungsten carbide bullets impacting at a sub-ballistic velocity of 360 km/h. The deformation behavior and sub-surface cracks were recorded by visual examination. Cr³⁺ fluorescence was used to measure the residual stress distribution on and beneath the impact site. The results show the alumina sintered at 1350 °C with a fine grain size of 1.7 μm and high hardness of 18.3 GPa is good at bulletproof due to the cone cracks can spread the dynamic stress effectively and consume much impact energy.