Mechanical Properties Of Aged Samples Research Articles

Multistage strain aging phenomenon of low-carbon steels with rolling pre-strain

In this study, a multistage strain aging method that used rolling pre-strain (compression) was developed to study the effects of temperature, and inter-pass time on static strain aging behavior of low carbon steel. An increase in hardness and strength caused by work hardening due to the forming process and aging at every stage of aging that is calculated separately. To comparing the effects of multistage aging against typical strain aging, the samples were rolled and subjected to the aging process both exist in typical one-stage aging that setting a 20% rolling pre-strain and in multiple stages pre-strain by setting a 5% rolling ratio in four stages. The mechanical properties of aged samples are compared with each other to study the effects of time and temperatures on strength and hardness. To evaluate the effects of pre-strain type (tensile or compression) on mechanical properties, one sample was subjected to tensile and compared with rolling pre-strain samples in similar conditions. The results show that in multistage static strain aged samples with rolling pre-strain, the peak of the strain stress curve occurs in 10–15 min rather than samples that aged after tensile pre-strain. Multistage strain aging increased samples’ strength by 10% and reduced their plasticity by 5%. To evaluate the effects of temperature on the time, we propose the maximum hardness and strength, the aging temperature of the samples was increased to 250 °C and it was observed that the maximum hardness and strength time is reduced by 10 min.

Evaluation of household waste materials for façade components in primary educational workshops. Degradation behavior and mechanical properties of aged samples

This article presents a pioneering experimental campaign on waste materials that rigorously tests numerous specimens to study their degradation behavior and the unreported mechanical properties of aged samples. The novel results of these tests, along with the mechanical properties and fire properties which new waste samples obtained from a previous article have are analyzed to check the feasibility of employing these household wastes in educational workshops for the self-construction of façades. Numerous previous studies on plastics degradation have analyzed the tensile strength reduction of polymers that compose the household waste studied in this project. However, no similar research projects on the degradation behavior of unprocessed Tetra Pak containers are reported in the literature. Most former studies were carried out in laboratories while few research projects studied waste degradation under real environmental conditions. The main results are: finding the unreported Tetra Pak mechanical properties of aged samples, discarding polystyrene household waste and some glues for exterior applications, and succeeding in introducing a TiO2-based finishing for Tetra Pak elements.

Effect of RRA heat treatment on corrosion and mechanical properties of AA7075

In this study, a retrogression process (R) has been applied to AA7075 at 180, 240, and 370°C for 15, 30, 90, and 120 min. After the retrogression, reaging treatment (RA) was reapplied with T6 conditions (120°C for 24 hr). The effect of different temperatures and time periods of retrogression and reaging temper on exfoliation corrosion (EXCO) of the AA7075 is examined. The EXCO solution was prepared in accordance with the ASTM G34‐01 standard and the samples were kept in the solution for 48 hr. Susceptibility of the alloy to EXCO was determined by weight loss detection, macro and microstructure studies, scanning electron microscope, transmission electron microscope, and energy dispersive X‐ray analyses. The mechanical properties of aged samples were determined by hardness, tensile tests, and fractography.

Properties of AA7075 aluminum alloy in aging and retrogression and reaging process

Abstract A retrogression process was applied to AA7075 alloy at 180, 240 and 320 °C for 1, 30, 50, 70, 90 and 120 min. After the retrogression, aging treatment was reapplied with T6 conditions (120 °C, 24 h). The mechanical properties of aged samples were determined by V-Charpy and hardness tests and also, physical properties of samples were determined by electrical conductivity tests. Moreover, microstructural properties were characterized by light microscope and transmission electron microscope. The results show that the effects of the temperature and the duration of the retrogression and reagent on the impact toughness and hardness are related to the precipitates at the grain boundary.

Thermal degradation and ageing behavior of microcomposites of natural rubber, carboxylated styrene butadiene rubber latices, and their blends

AbstractThe effect of microfillers on the thermal stability of natural rubber (NR), carboxylated styrene butadiene rubber (XSBR) latices, and their 70/30 NR/XSBR blend were studied using thermogravimetric method. Microcomposites of XSBR and their blend were found to be thermally more stable than unfilled samples. The activation energy needed for the degradation of polymer chain was calculated from Coats‐Redfern plot. Activation energy needed for the thermal degradation of filled samples was higher than unfilled system. It indicated the improved thermal stability of the filled samples. The ageing resistance of the micro‐filled samples was evaluated from the mechanical properties of aged samples. The thermal ageing was carried out by keeping the samples in hot air oven for 7 days at 70°C. The mechanical properties such as tensile strength, modulus at 300% elongation, and strain at break were computed. As compared to unfilled samples, micron‐sized fillers reinforced systems exhibited higher ageing resistance. Finally, an investigation was made on the influence of ion‐beam irradiation on microcomposites of NR, XSBR latices, and their 70/30 blend systems using 28Si8+ performed at 100 MeV. The surface changes of the samples after irradiation were analyzed using X‐ray photoelectron spectroscopy. The results of XPS measurements revealed that the host elements were redistributed without any change in binding energies of C1s, O1s, and Si2p. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Aging and cold crystallization of melt‐extruded poly(trimethylene terephthalate) films

AbstractWe analyzed the thermal crystallization, glass‐transition behavior, and mechanical properties of melt‐extruded poly(trimethylene terephthalate) (PTT) films to investigate their physical aging and annealing effects. The physical aging and annealing of PTT films had an influence on the glass‐transition temperature, recrystallization behavior, and mechanical properties. When samples were aged at an ambient temperature, the crystallization temperature decreased largely within 5 h, the heat of crystallization increased, and the breaking stress and breaking elongation increased. The glass‐transition temperature of annealed samples, which was obtained from differential scanning calorimetry and dynamic mechanical measurements, increased with increasing annealing temperature below 80 °C but decreased above that temperature. In addition, the glass‐transition temperature and modulus of annealed samples were largely affected by the annealing time; in particular, they increased sharply within 1 h on annealing at 50 °C. Consequently, the change in the glass‐transition temperature on annealing was ascribed to the fact that the molecular constraint due to recrystallization and the mobility of rigid amorphous PTT chains competed with each other, being dependent on the annealing temperature. The mechanical properties of aged samples were closely related to their cold‐crystallization behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1920–1927, 2001

Thermal aging behavior of an SiC-fiber reinforced glass matrix composite in a non-oxidizing atmosphere

The thermal aging in argon of a commercially available SiC-fiber reinforced glass matrix composite was investigated at temperatures in the range 500–700 °C for exposure duration of up to 1000 h. An inert atmosphere was used to study the effects of temperature alone, thus minimizing and neglecting the effects of oxidation. The mechanical properties of aged samples were evaluated at room-temperature by using four-point flexure strength and three-point flexure chevron-notch techniques. The interfacial properties were determined by push-out indentation measurements using an in-situ SEM indentation apparatus. The fracture toughness values determined by the chevron-notch tests were little affected by the aging conditions and were in the range 19–26 MPa√m . The frictional interfacial shear stress was not affected by the aging conditions either. For the most severe aging conditions investigated (1000 h at 600 °C and 100 h at 700 °C), a significant loss of flexure strength and stiffness of the samples was detected, which has been ascribed to microstructural changes that occurred in the material during aging as a consequence of the softening of the glass matrix. At these aging conditions, a lower interfacial shear stress for fiber-matrix debonding initiation was measured, which may be explained also by the occurrence of matrix softening and void formation.