بافت‌های مقاوم در برابر شکست پلی پروپیلن تقویت‌شده با الیاف بلند

An integral design and manufacturing concept for crash resistant

textile and long-fibre reinforced polypropylene structural components

یک طراحی انتگرالی و ایده‌ی تولید برای بافت‌های مقاوم در برابر شکست

و ترکیبات ساختاری پلی پروپیلن تقویت‌شده با الیاف بلند

ABSTRACT

For the design of crash resistant structures for automotive applications, mainly metallic materials are currently considered. However, the advanced specific energy absorption capacity and a high lightweight potential qualifies fiber and textile reinforced thermoplastic composites for such components. With a load adapted material design as well as an efficient manufacturing concept these properties can be exploited to a full extend. A seat pan is chosen as an exemplary structure to illustrate the four main aspects of the investigations: evaluation of glass fiber polypropylene composite configurations; development of a manufacturing and process chain; crash and impact experiments on structural level and numerical modelling strategy. Hybrid yarn based textiles, such as a commercially available 2/2-twill fabric and novel multi-layered flat bed weft-knitted fabrics have been considered to be combined with a long-fibre reinforced thermoplastic material (LFT, cutting length of 25 mm) for complexly loaded sections like ribbings. A special emphasis is set on a similar to mass-production manufacturing process. A fully automated integral hot pressing process has been developed, where an automated handling system places the conglomerate of extruded LFT-material and preheated hybrid yarn textile in a fast-stroke press, achieving process cycles of 45 s. Finally, the structural evaluation under crash loading conditions is compared against numerical results

 

تئوری جدید تأثیر مدیوم بر شبیه سازی انتقال حرارت مواد متخلخل

A novel effective medium theory for modelling

the thermal conductivity of porous materials

تئوری جدید تأثیر متوسط بر شبیه سازی انتقال حرارت مواد متخلخل

ABSTRACT

A novel effective medium theory was proposed to model the thermal conductivity of porous materials. In this theory, phases (or components) are treated as small spheres dispersing into an assumed uniform medium with the thermal conductivity km. A simple algebraic expression for the thermal conductivity based on this theory was derived, in which each has a distinct physical basis. The expression can unify five basic structural models (Series, Parallel, two forms of Maxwell–Eucken, effective medium theory) through variations of km. Furthermore, the feasibility of the model was evaluated using the experimental data from previous literatures and those calculated by this model.

 

ممانعت از خوردگی مس توسط ترکیب bipyrazole در 3% NaCl

Inhibition of copper corrosion by bipyrazole compound

in aerated 3% NaCl

ممانعت از خوردگی مس توسط ترکیب bipyrazole در 3% NaCl هوادهی شده

ABSTRACT

The corrosion behaviour of copper in aerated 3% NaCl solution was investigated by rotating electrode at various rates. The reduction of O2 obeys the Levich equation. The inhibition of the copper corrosion in aerated 3% NaCl solution was studied by using potentiodynamic polarisation and linear polarisation resistance (LRP) in the presence of different concentrations of a bipyrazolic compound named N,N-bis (3-carbomethoxy-5-methylpyrazol-1-ylmethyl) cyclohexylamine (BiPyA). The presence of this compound in the solution decreases the corrosion current density and increases the linear resistance polarisation. The inhibition efficiencies obtained from cathodic Tafel plots and LRP methods are in good agreement. BiPyA compound presents an efficient inhibitor of copper corrosion, acts as a mixed-type inhibitor and adsorbs on the copper surface according to the Langmuir isotherm model.

 

مقایسه جوشکاری EBW و اتصال خود فشاری حرارتی برای آلیاژ Ti6Al4V

A comparative study on electron beam welding and

rigid restraint thermal self-compressing bonding for Ti6Al4V alloy

بررسی مقایسه ای جوشکاری پرتوی الکترونی

و اتصال خود فشاری حرارتی سخت مقیدشده برای آلیاژ Ti6Al4V

ABSTRACT

This study focuses on the influence of joining method difference on the joint microstructure and properties. Unlike vacuum electron beam welding (EBW) utilizing electron beam as fusion heat source, rigid restraint thermal self-compressing bonding (TSCB), a new solid-state bonding method proposed by authors, employs vacuum electron beam as the non-melt heat source to bond materials in this work. Meanwhile, a comparative study on the microstructure and mechanical properties of EBWjoint and rigid restraint TSCB joint was conducted to investigate the effect of this difference on joint microstructure and properties. Results show that compared with EBW joints, the rigid restraint TSCB joints as solid-state joints are homogeneous in terms of microstructure and microhardness profile. Strength of both joints are comparable with that of base metal, but the elongation of the rigid restraint TSCB joint is more close to that of base metal. Rigid restraint TSCB joint has better combination of strength and ductility.

 

اثر اندازه نمونه بر ریزساختار فاز بین فلزی Al2Cu

Effect of sample size on intermetallic Al2Cu microstructure and

orientation evolution during directional solidification

اثر اندازه نمونه بر ریزساختار فاز بین فلزی Al2Cu

و روند جهت گیری آن در حین انجماد جهت دار

ABSTRACT

Al-40% Cu hypereutectic alloy samples were successfully directionally solidified at a growth rate of 10 μm/s in different sizes (4 mm, 1.8 mm, and 0.45 mm thickness in transverse section). Using the serial sectioning technique, the three-dimensional (3D) microstructures of the primary intermetallic Al2Cu phase of the alloy can be observed with various growth patterns, L-shape, E-shape, and regular rectangular shape with respect to growth orientations of the (110) and (310) plane. The L-shape and regular rectangular shape of Al2Cu phase are bounded by {110} facets. When the sample size was reduced from 4 mm to 0.45 mm, the solidified microstructures changed from multi-layer dendrites to single-layer dendrite along the growth direction, and then the orientation texture was at the plane (310). The growth mechanism for the regular faceted intermetallic Al2Cu at different sample sizes was interpreted by the oriented attachment mechanism (OA). The experimental results showed that the directionally solidified Al-40% Cu alloy sample in a much smaller size can achieve a well-aligned morphology with a specific growth texture.

 

پیوند نفوذی فاز مایع گذرا با استفاده از پوشش‎های نانوپراکنده‎ی Ni

Transient liquid phase diffusion bonding Al-6061 using

nano-dispersed Ni coatings

پیوند نفوذی فاز مایع گذرا با استفاده از پوشش‎های نانوپراکنده‎ی Ni

ABSTRACT

Transient liquid phase diffusion bonding (TLPDB) of Al-6061 containing 15 vol.% alumina particles was carried out at various bonding temperatures. A 5 μm thick electrodeposited Ni-coating containing 18 vol.% nano-size alumina particles was used at the interlayer. Joint formation was attributed to the solid-state diffusion of Ni into the Al-6061 alloy followed by eutectic formation and isothermal solidification at the joint interface. Examination of the joint region using scanning electron microscopy (SEM), wavelength dispersive spectroscopy (WDS) and X-ray diffraction (XRD) showed the formation of intermetallic phases such as Al3Ni, Al9FeNi and Ni3Si within the joint zone. The results indicate that the incorporation of nano-size Al2O3 dispersions into the interlayer can be used to improve joint strength.

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