اثر سرعت جوشکاری بر تنش پسماند در طول جوشکاری قوس با الکترود تنگستن تحت پوشش گاز

Influence of welding speed and power on residual stress during gas tungsten arc welding (GTAW) of thin sections

with constant heat input: A study using numerical simulation and experimental validation

اثر سرعت جوشکاری و توان بر تنش پسماند

در طول جوشکاری قوسی الکترود تنگستن (GTAW) مقاطع نازک با ورودی گرمای ثابت

مطالعه ای با استفاده از شبیه سازی و اعتبارسنجی تجربی

ABSTRACT

The temperature distribution and residual stresses for a GTAW circumferential butt joint of AISI 304 stainless steel using numerical simulation have been evaluated. For evaluation of weld induced residual stresses, the analysis of heat source fitting was carried out with heat inputs ranging from 200 to 500 J/mm to arrive at optimal heat input for obtaining proper weld penetration and heat affected zone (HAZ). For this chosen heat input, the influence of different weld speeds and powers on the temperature distribution and the residual stresses is studied. The heat source analysis revealed the best choice of heat input as 300 J/mm. The residual stresses on the inner and outer surfaces, and along the radial direction were computed. Increase in temperature distribution as well as longitudinal and circumferential residual stresses was observed with the increase in weld speed and power. The validity of the results obtained from numerical simulation is demonstrated with full scale shop floor welding experiments.

 

رفتار سینترینگ و خواص دی الکتریکی سرامیک ها

Sintering behavior and dielectric properties of BaTiO3 ceramics with glass addition for internal capacitor of LTCC

رفتار سینترینگ و خواص دی الکتریکی سرامیک های BaTiO3 با افزودنی شیشه برای خازن داخلی LTCC 

ABSTRACT

The addition effects of ZnO–B2O3–SiO2 (ZBS) glass on both the sintering behavior and dielectric properties of BaTiO3 were investigated in developing low-temperature-fired BaTiO3-based ceramics for LTCC devices. X-ray diffractometer (XRD), scanning electron microscopy (SEM), and a dilatometer were used to examine the effect of ZBS glass on BaTiO3 densification and the chemical reaction between the glass and BaTiO3. The results indicate that ZBS glass can be used as a sintering aid to reduce the sintering temperature of BaTiO3 from 1300 to 900 ◦C without secondary phase formation. The dielectric properties of BaTiO3 with ZBS glass sintered at 900 ◦C show a relative density of 95%, a high dielectric constant of 994, and a dielectric loss of 1.6%.

 

انتقال حرارت و رفتارانجماد پوسته‎ای در قالب ریخته‎گری پیوسته

Heat Transfer and Deformation Behavior of Shell Solidification

in Wide and Thick Slab Continuous Casting Mold

انتقال حرارت و رفتار تغییرشکل انجماد پوسته‎ای در ورق بزرگ و ضخیم قالب ریخته‎گری پیوسته

ABSTRACT

The shell solidification in continuous casting mold is a rather complex process that is coupled with thermal and mechanical behaviors, which are related to numerous of defects occurring in slabs surface and subsurface during practical continuous casting. Intending to increase the understanding of shell thermal and mechanical behaviors in continuous casting molds to improve the casting process, numerous studies[1-13] have been conducted over the past few decades by numerical simulation. However, among these previous studies, most of the mathematical models neglected the effects of mold flux film on shell heat transfer[1-6,11] or assumed that the mold flux film distribution in shell/mold gap was uniform or changed linearly with the mold height[7-10,12,13]. It is obvious that the assumptions did not conform to the actual case of practical continuous casting that the mold flux film in mold distributes dynamically both along mold height and circumference with the evolutions of shell/mold gap and shell temperature, and affects the shell thermal and mechanical behaviors greatly.

جوشکاری GTAW آلیاژ آلومینیوم تیتانیوم

Effect of Vibration during GTAW Welding on Microstructure and Mechanical Properties of Ti6Al4V

تاثیر ارتعاش در طی جوشکاری GTAW روی ریزساختار و خواص مکانیکی Ti6Al4V 

ABSTRACT

The drive to improve weld quality and process parameters demands the use of improved welding tech niques and materials [1]. Titanium and its alloys are considered to be the best engineering metals for indus trial applications because of their excellent strengthto weight ratio, high fatigue life, toughness, resistance to corrosion and good fatigue strength [2, 3].

Welding methods such as gas tungsten arc, resis tance, and diffusion welding have been developed in response to the expansion of the titanium industry. 

Titanium alloys easily absorb harmful gases because of their high chemical activity, resulting in poor mechanical properties and unstable structure [4, 5]. Gas tungsten arc welding is the preferred method for avoiding these deficiencies [6]. The weld ing of titanium alloys often increases grain size in the welded metal and heat affected zones [7]. Fusion zones typically exhibit coarse columnar grains in response to prevailing thermal conditions during welded metal solidification [6]. These columnar grains produce inferior mechanical properties in the welds [1]. Methods of weld grain refinement include inocu with heterogeneous nucleants, surface nucleation induced by gas impingement, introduction of physical disturbance through techniques such as elec tromagnetic stirring [4]. Vibratory techniques, and pulsed current welding techniques [8].

رفتار استحاله سرد شدن پیوسته فولاد خط لوله‎ی X70

Continuous cooling transformation behavior of X70 pipeline steel

رفتار استحاله سرد شدن پیوسته فولاد خط لوله‎ی X70 

ABSTRACT

The comprehensive mechanical properties of steel depended on the final microstructure and grain refinement. In order to obtain high performance pipeline steel, composition design and the application of controlled rolling and controlled cooling technology had become a key, especially the latter which had decisive influence on the product’s final texture and comprehensive performance in modern iron and steel material production. Along with the development of the modern rolling equipment as well as the in-depth study of controlled rolling and controlled cooling technology, the application of controlled rolling and controlled cooling technology had become an important means of fully excavating the potential of the material properties based on the existing material chemical compositions and it had got the extensive attention from modern iron and steel materials research field.

مشخصه‎های ضخامت پوسته در ورق تولید شده به روش ریخته‎گری مداوم

Characteristics of shell thickness in a slab continuous casting mold

مشخصه‎های ضخامت پوسته در ورق تولید شده به روش ریخته‎گری مداوم 

ABSTRACT

It is of great importance to form a thick and sufficiently uniform solidifying shell in the mold to prevent breakout in the continuous casting process. Breakout starts to take place at the thinnest point commonly, and therefore, it is significant to investigate the slab thickness distribution in longitudinal and transverse directions to determine this point. Experimental and numerical simulations are the two ways for  measurement of shell thickness in the mold. The former such as adding sulfur into the mold [1], disturbs the normal production and obtains some useful data, which cannot characterize the shell thickness profiles thoroughly. On the other hand, several scholars have researched the flow, heat transfer, and solidification in the mold by numerical simulation . However, some profound researches on the characteristics of the shell thickness have been done.

  

غرق شدن تایتانیک بعلت مشکل متالورژیکی

RMS Titanic: A Metallurgical Problem

آر ام اس تایتانیک : یک مشکل متالورژیکی

ABSTRACT

On 14 April 1912, at 11:40 p.m., Greenland Time, the Royal Mail Ship Titanic on its maiden voyage was proceeding westward at 21.5 knots (40 km/h) when the lookouts on the foremast sighted a massive iceberg estimated to have weighed between 150,000 to 300,000 tons at a distance of 500 m ahead. Immediately, the ship’s engines were reversed and the ship was turned to port (left) in an attempt to avoid the iceberg. In about 40 seconds, the ship struck the iceberg below the waterline on its starboard (right) side near the bow. The iceberg raked the hull of the ship for 100 m, destroying the integrity of the six forward watertight compartments. Within 2 h 40 min the RMS Titanic sank.

Metallurgical examination and chemical analysis of the steel taken from the Titanic revealed important clues that allow an understanding of the severity of the damage inflicted on the hull. Although the steel was probably as good as was available at the time the ship was constructed, it was very inferior when compared with modern steel. The notch toughness showed a very low value (4 joules) for the steel at the water temperature (−2 °C) in the North Atlantic at the time of the accident.

 

تاثیر فرایند تمپر بر ساختار و خواص مکانیکی فولاد HSLA-100

Influence of tempering on the microstructure and

mechanical properties of HSLA-100 steel plates

تاثیر فرایند تمپر بر ریزساختار و خواص مکانیکی صفحات فولادی HSLA-100

ABSTRACT

The influence of tempering on the microstructure and mechanical properties of HSLA-100 steel (with C-0.04, Mn-0.87, Cu-1.77, Cr-0.58, Mo-0.57, Ni-3.54, and Nb-.038 pct) has been studied. The plate samples were tempered from 300 °C to 700 °C for 1 hour after austenitizing and water quenching. The transmission electron microscopy (TEM) studies of the as-quenched steel revealed a predominantly lath martensite structure along with fine precipitates of Cu and Nb(C, N). A very small amount of retained austenite could be seen in the lath boundaries in the quenched condition. Profuse precipitation of Cu could be noticed on tempering at 450 °C, which enhanced the strength of the steel significantly (yield strength (YS)—1168 MPa, and ultimate tensile strength (UTS)—1219 MPa), though at the cost of its notch toughness, which dropped to 37 and 14 J at 25 °C and −85 °C, respectively. The precipitates became considerably coarsened and elongated on tempering at 650 °C, resulting in a phenomenal rise in impact toughness (Charpy V-notch (CVN) of 196 and 149 J, respectively, at 25 °C and −85 °C) at the expense of YS and UTS. The best combination of strength and toughness has been obtained on tempering at 600 °C for 1 hour (YS-1015 MPa and UTS-1068 MPa, with 88 J at −85 °C)

 

کامپوزیت‎های تقویت شده با الیاف سه بعدی فیبر شیشه-پلی پروپیلن

Polypropylene/glass fibre 3D-textile reinforced composites

for automotive applications

کامپوزیت‎های تقویت شده با الیاف سه بعدی فیبر شیشه/پلی پروپیلن

برای کاربردهای خودرو

ABSTRACT

Textile-reinforced thermoplastic composites offer huge application potentials for a rapid manufacturing of components with versatile possibilities of integrating functions. However, an application of these new materials requires the knowledge of the directional dependent material properties. In this study, results are presented concerning selected relevant load cases for industrial applications. For the new group of multi-layered flat bed weft-knitted glass fibre/polypropylene composites (MKF-GF/PP), tensile tests under different temperatures and test velocities have been carried out as well as Charpy impact tests, open hole tension tests and dynamic-mechanical analysis. The mechanical properties of MKF-GF/PP and unidirectional GF/PP composites with tailored fibre surface and interphase, respectively, have been compared to those of woven GF/PP composites and GF/PP composites made of non-crimp fabrics (NCF) as a benchmark.

 

کامپوزیت‎های تقویت شده با الیاف سه بعدی فیبر شیشه-پلی پروپیلن

Polypropylene/glass fibre 3D-textile reinforced composites

for automotive applications

کامپوزیت‎های تقویت شده با الیاف سه بعدی فیبر شیشه/پلی پروپیلن

برای کاربردهای خودرو

ABSTRACT

Textile-reinforced thermoplastic composites offer huge application potentials for a rapid manufacturing of components with versatile possibilities of integrating functions. However, an application of these new materials requires the knowledge of the directional dependent material properties. In this study, results are presented concerning selected relevant load cases for industrial applications. For the new group of multi-layered flat bed weft-knitted glass fibre/polypropylene composites (MKF-GF/PP), tensile tests under different temperatures and test velocities have been carried out as well as Charpy impact tests, open hole tension tests and dynamic-mechanical analysis. The mechanical properties of MKF-GF/PP and unidirectional GF/PP composites with tailored fibre surface and interphase, respectively, have been compared to those of woven GF/PP composites and GF/PP composites made of non-crimp fabrics (NCF) as a benchmark.