کامپوزیت SiC-SiC در آزمون خزش و خستگی

Stress, strain and elastic modulus behaviour of

SiC/SiC composites during creep and cyclic fatigue

رفتار تنش، کرنش و مدول کشسانی کامپوزیت SiC/رشته ی SiC

در آزمون خرش و خستگی چرخه ای

ABSTRACT

Creep and fatigue tests of Hi-NicalonTM/SiC (SiC matrix contains glass-forming, boron-based particulates), Standard SiC/SiC (SiC matrix is pure SiC) and Enhanced SiC/SiC (SiC matrix contains glass-forming, boron-based particulates) were carried out in air at 1300°C. The stress–strain hysteresis loops during fatigue and creep were studied. The change of Young’s modulus during creep and fatigue was analysed and compared among the three kinds of materials. Creep strain rates of Hi-NicalonTM/SiC in air were similar to those of Enhanced SiC/SiC, but much lower than those of Standard SiC/SiC. Consequently, the time to rupture at a given stress in Hi-NicalonTM/SiC was similar to that in Enhanced SiC/SiC, but much longer than in Standard SiC/SiC. Fatigue resistance of Hi-NicalonTM/SiC was similar to that of Enhanced SiC/SiC, but much better than Standard SiC/SiC.

 

ساختار و استحکام کامپوزیت کربن- تقویت شده با کربن

Strength and structure of carbon–carbon reinforced composite

ساختار و استحکام کامپوزیت کربن- تقویت شده با کربن

ABSTRACT

The atomistic simulations of carbon nanotube (CNT) – carbon reinforced composite material are reported. The studied composite samples are obtained by impregnating certain amounts of CNTs (3,3) and (6,6) into a pristine graphite matrix. The addition of CNTs is found to be of significant usefulness for the CNT–reinforced composites, since it allows to achieve extreme lightness and strength. Being impregnated into graphite matrix, CNTs are able to increase the critical component of its initially highly anisotropic Young modulus by 2–8 times. The linear thermal expansion coefficients do not exceed 10−6 to 10−5 K−1, making this material applicable for novel aviation and space vehicles. The degree of dispersion of CNTs within graphite matrix is found to drastically influence composite properties.

 

رفتار اصطکاکی و سایشی کامپوزیت های سرامیک- آلیاژ آلومینیوم

Friction and Wear Behaviour of Brake Pads Dry Sliding Against

Semi-Interpenetrating Network Ceramics/Al-alloy Composites

رفتار اصطکاکی و سایشی ناشی از سایش خشک لنت های ترمز بر روی

شبکه نیمه نفوذی کامپوزیت های سرامیک/ آلیاژ آلومینیومی 

ABSTRACT

Semi-interpenetrating network composites containing 40 vol.% ceramics (5Al2O3·8SiO2) and 60 vol.% Al-alloy were fabricated in place of cast iron available for automotive brake rotors. The friction and wear performances of brake pads dry sliding against the composites were measured using a SRV testing machine. The test procedures include friction fade and recovery, load sensitivity at 100 and 250°C, and wear. The friction was found to increase first and then decrease with increasing temperature, followed by the inverse recovery upon cooling. Wear showed an incremental tendency over a wide temperature range. For loads from 40 to 160 N, the friction decreased at 100 and 250°C. At load below 128 N, the former friction was inferior to the latter while at load above 128 N the friction exhibited an inverse tendency. Wear mildly increased with load at 100 °C and decreased dramatically at 250 °C. SEM and EDS investigations revealed that the worn pad surfaces at 250 °C were covered by more tribofilms, including more coke and graphite with friction-reducing action as well as fewer compounds (corresponding to Si and Al) with friction-increasing action in comparison with those at 100 °C. The compression of the tribofilms contributed to a large decrease in the friction and wear with increasing load. However, at 100 °C E-glass fibers exposed at the worn surfaces inhibited the excessive wear of the pad despite lack of more tribofilms. Their glossy surfaces decreased the friction. The proposed friction models explain some friction and wear behaviour better.

 

رفتار خوردگی-خستگی آلیاژ آلومینیوم 7075-T651 تحت بارگذاری های متناوب

Corrosion-fatigue behaviour of 7075-T651 aluminum

alloy subjected to periodic overloads

رفتار خوردگی-خستگی آلیاژ آلومینیوم 7075-T651  تحت بارگذاری های متناوب

ABSTRACT

The corrosion-fatigue behaviour of 7075-T651 aluminum alloy subjected to periodic overloads was examined. This aluminum alloy is typically used in aerospace structural components such as the wing spars of aircraft. Axial fatigue specimens were subjected to a loading spectrum that consisted of a fully reversed periodic overload of near-yield magnitude followed by 200 smaller cycles at high Rratio. The specimens were fatigue tested while they were fully immersed in an aerated and recirculated 3.5 wt% NaCl simulated seawater solution.

 

رشد ورقه های گرافن روی نانوسیم های سیلیکا با دانسیته بالا

Catalyst-free approach for growth of graphene sheets on

high-density silica nanowires byCVD

روش بدون کاتالیزور برای رشد ورقه های گرافن روی نانوسیم های سیلیکا

با دانسیته بالا توسط CVD 

ABSTRACT

A novel “two-step annealing” method is proposed for the direct synthesis of graphene sheets on high-density dielectric silica nanowires without using metal catalysts. During the first annealing at 1000 °C, the extremely thin SiO2 layer on Si substrate shrinks and forms dense nanoparticles. Using these silica nanoparticles as templates, graphene sheets and silica nanowires are synthesized simultaneously after the second annealing process at 800–850 °C. The experiment results suggest that the graphene sheets grow along the nanowires and its crystalline quality and domain size are determined by the temperature and duration of the second annealing process.

 

فشار انفجاری لوله‎های فولاد زنگ‎نزن تحت کشش، فشار و دمای بالا

Burst pressure of super duplex stainless steel pipes subject to

combined axial tension, internal pressure and elevated temperature

فشار انفجاری لوله‎های فولاد زنگ‎نزن ابردوتایی در معرض سه مشخصه‎ی

کشش محوری ترکیبی، فشار داخلی و دمای بالا

ABSTRACT

The burst pressure of super duplex stainless steel pipe is measured under combined internal pressure, external axial tension and elevated temperature up to 160 °C. The experimental results are compared with existing burst pressure prediction models. Existing models are found to provide reasonable estimate of the burst pressure at room temperature but significantly over estimate the burst pressure at elevated temperature. Increasing externally applied axial stress and elevated temperature reduces the pressure capacity.

 

انتخاب پوشش Coating Selection

Coating Selection

انتخاب پوشش

ABSTRACT

An improved approach to coating selection should thus allow progressive elimination and lend itself to a computerised implementation. Furthermore, an approach which avoids the identification of one dominant wear mechanism would be desirable. A systematic framework fulfilling these goals is described below. This is intended to provide a basis for minimising the probability of tribological problems by indicating the material property limitations and characteristics needed (Matthews et. al., 1992b). 

 

مشخصه یابی ریزساختارها و انحراف جهت گیری رشد دندریت فاز Al2Cu

Characterization of microstructures and growth orientation deviating

of Al2Cu phase dendrite at different directional solidification rates

مشخصه یابی ریزساختارها و انحراف جهت گیری رشد دندریت فاز Al2Cu

در نرخ های انجماد جهت دار مختلف 

ABSTRACT

At different directional solidification rates (10, 20 and 100 mm/s), microstructures and growth orientation variations of Al2Cu dendrite in Al-40%Cu alloy were characterized. When solidification rates were ranged from 10 to 100 mm/s, three-dimensional microstructure of Al2Cu dendrite changed from faceted L-shaped patterns to non-faceted complex dendrite morphology in transverse section. By the macro and micro orientation analysis characterize methods, [001] growth direction of Al2Cu dendrites with different morphologies was determined. The deviation angle between [001] direction and the heat flow direction was increased with solidified rate increasing. The experimental results showed that the regular solidified microstructure and growth orientation along the heat flow direction could be well controlled under lower directional solidification rate.

 

جذب و جمع آوری الکترون در سلول های خورشیدی

Enhanced absorbance and electron collection in inverted organic

solar cells: Optical admittance and transient photocurrent analyses

بهبود جذب و جمع آوری الکترون در سلول های خورشیدی آلی معکوس:

 ورود یا گذر نوری و آنالیز از فوتون گذار

ABSTRACT

Optical admittance analysis reveals that light absorption in inverted organic solar cells (OSCs), based on the same polymer blend layer of regio-regular poly(3-hexylthiophene):[ 6,6]-phenyl-C61-butyric acid methyl ester (PCBM), is always greater than their regular geometry OSCs fabricated using an ITO/poly(3,4-ethylene dioxythiophene):(polystyrene sulfuric acid) anode. Transient photocurrent measurements elucidate that interfacial exciton dissociation at the cathode interfaces of Al-modified ITO/ PCBM (inverted cell) and Al/PCBM (regular cell) is not equivalent. It is shown that the reverse configuration allows improving the absorbance of the cell, favoring charge collection at cathode/PCBM interface and also possessing a dawdling degradation behavior as compared to a control regular OSC in the accelerated aging test.

 

سنتز دما پایین فیلم های نازک ZnO دوپ شده با سدیم و آلومینیوم

Low temperature synthesis wide optical band gap Al and

Al, Na) co-doped ZnO thin films)

سنتز دما پایین فیلم های نازک ZnO داپ همزمان شده با Al و Na

با باندگپ نوری گسترده

ABSTRACT

With a wide bandgap of 3.37 eV and a large exciton binding energy of 60meV at room temperature, zinc oxide (ZnO), like GaN, is considered as an important material for blue and ultra-violet optical devices. Its research interest arisen again since 1957, the New Jersey Zinc Company published a book entitled “Zinc Oxide Rediscovered” to promote the material’s “frontier” properties (such as semiconductor, luminescent, catalytic, ferrite, photoconductive, and photochemical properties) and illustrative applications. Recently, research focused mainly on fabrication of high quality single crystals and epitaxial layers, in order to fully realize ZnObased electronic and optoelectronic devices.