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  1. [11]
    مهندس مواد و معادن
    مهندس مواد و معادن غير متواجد حالياً
    عضو


    تاريخ التسجيل: Aug 2007
    المشاركات: 36
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    بسم الله الرحمن الرحيم

    السلام عليكم

    ان عملية سحب الاسلاك على البارد تولد اجهادات (Stress) و ايضا تحريك و تجميع و زيادة كثافة الانخلاعات (Dislocations) مما يؤدي الى بعثرة و تشويش الالكترونات مما يودي الى تقليل التوصيل الكهربائي و زيادة المقاومة (Electrical Resistivity)

    لم اقصد ان هناك اعادة تبلور في عملية سحب الاسلاك على البارد لكن هنالك تغير في شكل الحبيبات Graines فيتغير شكلها الى حبيبات طولية باتجاه السحب لكن عن المعالجة الحرارية يجب ان تكون درجة الحرارة كافية للوصول الى اعادة التبلور.

    بالنسبة للمعالجة الحرارية للنيكل صحيح تحتاج الى درجة حرارة عالية تقريبا 1135 درجة مؤية لعمل Annealing . يمكن الحصول على هذه الدرجة بسهولة باستخدام افران المقاومة الكهربائية لكن تكلفتها مرتفعة نسبيا
    و يفضل استخادم افران فاكيوم معزولة عن الهواء لكي لا يحدث تاكد و فقد عناصر اثناء المعالجة الحرارية او استخدام وسط خامل مثل غاز الارجون.
    كل هذه العمليات تعتمد على كلفة التصنيع و مقدار الربح المرجو من المنتج و الجودة المراد الحصول عليها.

    ممكن ان يتم تقليل ال Stress عن طريق زيادة مراحل السحب للاسلاك و بالتالي تقليل نسبة التغير التي تحدث لقطر السلك يعني نسبة تقليل القطر من مرحلة الى اخرى نصف ملم فقط
    و يمكن عمل تعديل على تصميم القوالب Dies بحيث يتم التحكم في زواياها مما يقلل الاحتكاك و الاجهادات.

    هناك طرق حديثة جدا لتقليل الاجهادات عن طريق الموجات فوق الصوتية Ultrasonic waves.


    بالنسبة للكتب الحمدلله عندي الكثير لكنها ليست كتب الكترونية و لا استطيع ان ارفعها على المنتدى

    ارجو ان تكون اجابتي صحيح او فيها فائدة

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  2. [12]
    عرااااقية
    عرااااقية غير متواجد حالياً
    عضو فعال
    الصورة الرمزية عرااااقية


    تاريخ التسجيل: Apr 2007
    المشاركات: 96
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    اقتباس المشاركة الأصلية كتبت بواسطة مهندس مواد و معادن مشاهدة المشاركة
    بسم الله الرحمن الرحيم

    السلام عليكم

    ان عملية سحب الاسلاك على البارد تولد اجهادات (Stress) و ايضا تحريك و تجميع و زيادة كثافة الانخلاعات (Dislocations) مما يؤدي الى بعثرة و تشويش الالكترونات مما يودي الى تقليل التوصيل الكهربائي و زيادة المقاومة (Electrical Resistivity)

    لم اقصد ان هناك اعادة تبلور في عملية سحب الاسلاك على البارد لكن هنالك تغير في شكل الحبيبات Graines فيتغير شكلها الى حبيبات طولية باتجاه السحب لكن عن المعالجة الحرارية يجب ان تكون درجة الحرارة كافية للوصول الى اعادة التبلور.

    بالنسبة للمعالجة الحرارية للنيكل صحيح تحتاج الى درجة حرارة عالية تقريبا 1135 درجة مؤية لعمل Annealing . يمكن الحصول على هذه الدرجة بسهولة باستخدام افران المقاومة الكهربائية لكن تكلفتها مرتفعة نسبيا
    و يفضل استخادم افران فاكيوم معزولة عن الهواء لكي لا يحدث تاكد و فقد عناصر اثناء المعالجة الحرارية او استخدام وسط خامل مثل غاز الارجون.
    كل هذه العمليات تعتمد على كلفة التصنيع و مقدار الربح المرجو من المنتج و الجودة المراد الحصول عليها.

    ممكن ان يتم تقليل ال Stress عن طريق زيادة مراحل السحب للاسلاك و بالتالي تقليل نسبة التغير التي تحدث لقطر السلك يعني نسبة تقليل القطر من مرحلة الى اخرى نصف ملم فقط
    و يمكن عمل تعديل على تصميم القوالب Dies بحيث يتم التحكم في زواياها مما يقلل الاحتكاك و الاجهادات.

    هناك طرق حديثة جدا لتقليل الاجهادات عن طريق الموجات فوق الصوتية Ultrasonic waves.


    بالنسبة للكتب الحمدلله عندي الكثير لكنها ليست كتب الكترونية و لا استطيع ان ارفعها على المنتدى

    ارجو ان تكون اجابتي صحيح او فيها فائدة




    السلام عليكم اخي وبارك الله بك وجعل الله في ميزان حسناتك بصراحة اجابتك كافية لانني لم اكن افهم شي عن المواد لان اختصاصي الكترونيك
    سؤالي الاخير ماسم الكتب الذي ممكن ان استفاد منها
    شكرا اخي وتعبتك معي

    اختكم عرااااقية

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  3. [13]
    مهندس مواد و معادن
    مهندس مواد و معادن غير متواجد حالياً
    عضو


    تاريخ التسجيل: Aug 2007
    المشاركات: 36
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    السلام عليكم

    اسم الكتب التي ممكن ان تفيدك

    Heat Treater's Guide Practices and Procedures for Nonferrous Alloys ASM international

    Metal forming Mechanics and Metallurgy , William F.Hosford and Robert M.Caddell

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  4. [14]
    عرااااقية
    عرااااقية غير متواجد حالياً
    عضو فعال
    الصورة الرمزية عرااااقية


    تاريخ التسجيل: Apr 2007
    المشاركات: 96
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    السلام عليكم

    مشكور اخي على التعب الله يوفقك يارب

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  5. [15]
    احمد1970
    احمد1970 غير متواجد حالياً
    عضو فعال جداً


    تاريخ التسجيل: May 2007
    المشاركات: 224
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  6. [16]
    محمد65
    محمد65 غير متواجد حالياً
    عضو


    تاريخ التسجيل: Aug 2006
    المشاركات: 39
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    السلام عليكم
    اشكركم جميعا من كل قلبي

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  7. [17]
    مهندسسسس
    مهندسسسس غير متواجد حالياً
    عضو


    تاريخ التسجيل: Sep 2007
    المشاركات: 17
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    أخواني الكرام .....

    السلام عليكم .... أحببت أن أدعم مشاركة الزميل مهندس مواد و معادن في حديثه عن الخلائط الحافظة للذاكرة

    I. What are Shape Memory Alloys?

    Shape memory alloys (SMA's) are metals, which exhibit two very unique properties, pseudo-elasticity, and the shape memory effect. Arne Olander first observed these unusual properties in 1938 (Oksuta and Wayman 1998), but not until the 1960's were any serious research advances made in the field of shape memory alloys. The most effective and widely used alloys include NiTi (Nickel - Titanium), CuZnAl, and CuAlNi.
    II. Applications of Shape Memory Alloys:

    The unusual properties mentioned above are being applied to a wide variety of applications in a number of different fields. Some of the most promising applications of SMAs are: -

    · Aeronautical Applications
    · Surgical Tools
    · Muscle Wires

    III. How Shape Memory Alloys Work:


    The two unique properties described above are made possible through a solid state phase change, that is a molecular rearrangement, which occurs in the shape memory alloy. Typically when one thinks of a phase change a solid to liquid or liquid to gas change is the first idea that comes to mind. A solid state phase change is similar in that a molecular rearrangement is occurring, but the molecules remain closely packed so that the substance remains a solid. In most shape memory alloys, a temperature change of only about 10°C is necessary to initiate this phase change. The two phases, which occur in shape memory alloys, are Martensite, and Austenite.

    Martensite, is the relatively soft and easily deformed phase of shape memory alloys, which exists at lower temperatures. The molecular structure in this phase is twinned which is the configuration shown in the middle of Figure 2. Upon deformation this phase takes on the second form shown in Figure 2, on the right. Austenite, the stronger phase of shape memory alloys, occurs at higher temperatures. The shape of the Austenite structure is cubic, the structure shown on the left side of Figure 2. The un-deformed Martensite phase is the same size and shape as the cubic Austenite phase on a macroscopic scale, so that no change in size or shape is visible in shape memory alloys until the Martensite is deformed.


    Figure 2: Microscopic and Macroscopic Views of the Two Phases of Shape Memory Alloys

    The temperatures at which each of these phases begin and finish forming are represented by the following variables: Ms, Mf, As, Af. The amount of loading placed on a piece of shape memory alloy increases the values of these four variables as shown in Figure 3. The initial values of these four variables are also dramatically affected by the composition of the wire (i.e. what amounts of each element are present).
    Mf Ms As Af




    Load
    Martensite

    Austenite


    Temperature
    Figure 3: The Dependency of Phase Change Temperature on Loading
    Shape Memory Effect:

    Figure 4: Microscopic Diagram of the Shape Memory Effect

    The shape memory effect is observed when the temperature of a piece of shape memory alloy is cooled to below the temperature Mf. At this stage the alloy is completely composed of Martensite, which can be easily deformed. After distorting the SMA the original shape can be recovered simply by heating the wire above the temperature Af. The heat transferred to the wire is the power driving the molecular rearrangement of the alloy, similar to heat melting ice into water, but the alloy remains solid. The deformed Martensite is now transformed to the cubic Austenite phase, which is configured in the original shape of the wire.

    The Shape memory effect is currently being implemented in:

    • Coffepots
    • The space shuttle
    • Thermostats
    • Vascular Stents
    • Hydraulic Fittings (for Airplanes)
    Pseudo-elasticity:



    Figure 5: Load Diagram of the pseudo-elastic effect Occurring


    Pseudo-elasticity occurs in shape memory alloys when the alloy is completely composed of Austenite (temperature is greater than Af). Unlike the shape memory effect, pseudo-elasticity occurs without a change in temperature. The load on the shape memory alloy is increased until the Austenite becomes transformed into Martensite simply due to the loading; this process is shown in Figure 5. The loading is absorbed by the softer Martensite, but as soon as the loading is decreased the Martensite begins to transform back to Austenite since the temperature of the wire is still above Af, and the wire springs back to its original shape.

    Some examples of applications in which pseudo-elasticity is used are:

    • Eyeglass Frames
    • Medical Tools
    • Cellular Phone Antennae
    • Orthodontic Arches
    IV. Advantages and Disadvantages of Shape Memory Alloys:

    Some of the main advantages of shape memory alloys include:
    • Bio-compatibility
    • Diverse Fields of Application
    • Good Mechanical Properties (strong, corrosion resistant)
    There are still some difficulties with shape memory alloys that must be overcome before they can live up to their full potential. These alloys are still relatively expensive to manufacture and machine compared to other materials such as steel and aluminum. Most SMA's have poor fatigue properties; this means that while under the same loading conditions (i.e. twisting, bending, compressing) a steel component may survive for more than one hundred times more cycles than an SMA element.

    Applications: -

    q Robotic Muscles:


    There have been many attempts made to re-create human anatomy through mechanical means. The human body however, is so complex that it is very difficult to duplicate even simple functions. Robotics and electronics are making great strides in this field, of particular interest are limbs such hands, arms, and legs.

    In order to reproduce human extremities there are a number of aspects that must be considered:

    • The gripping force required to manipulate different objects (eggs, pens, tools)
    • The motion capabilities of each joint of the hand
    • The ability to feel or touch objects (tactile senses)
    • The method of controlling movement within the limb
    • Emulating real human movement (smoothness, and speed of response).

    University of Alberta


    Many different solutions have been proposed for this problem, some include using "muscles" controlled by air pressure, piezoelectric materials, or shape memory alloys. Shape memory alloys mimic human muscles and tendons very well. SMA's are strong and compact so that large groups of them can be used for robotic applications, and the motion with which they contract and expand are very smooth creating a life-like movement unavailable in other systems.
    Creating human motion using SMA wires is a complex task but a simple explanation is detailed here. For example to create a single direction of movement (like the middle knuckle of your fingers) the setup shown in Figure 1 could be used. The bias spring shown in the upper portion of the finger would hold the finger straight, stretching the SMA wire, then the SMA wire on the bottom portion of the finger can be heated which will cause it to shorten bending the joint downwards (as in Figure 1). The heating takes place by running an electric current through the wire; the timing and magnitude of this current can be controlled through a computer interface used to manipulate the joint.

    There are still some challenges that must be overcome before robotic hands can become more commonplace. The first is generating the computer software used to control the artificial muscle systems within the robotic limbs. The second is creating large enough movements to emulate human flexibility (i.e. being able to bend the joints as far as humans can). The third problem is reproducing the speed and accuracy of human reflexes.
    Figure 1
    q Aircraft Maneuverability:

    Aircraft maneuverability depends heavily on the movement of flaps found at the rear or trailing edge of the wings. The efficiency and reliability of operating these flaps is of critical importance.

    Most aircraft in the air today operate these flaps using extensive hydraulic systems. These hydraulic systems utilize large centralized pumps to maintain pressure, and hydraulic lines to distribute the pressure to the flap actuators. In order to maintain reliability of operation, multiple hydraulic lines must be run to each set of flaps. This complex system of pumps and lines is often relatively difficult and costly to maintain.

    Many alternatives to the hydraulic systems are being explored by the aerospace industry. Among the most promising alternatives are piezoelectric fibers, electrostrictive ceramics, and shape memory alloys.

    The flaps on a wing generally have the same layout shown on the left, with a large hydraulic system like the one shown in Figure 2 attached to it at the point of the actuator connection. "Smart" wings, which incorporate shape memory alloys, are typically like the wing shown in Figure 3, this system is much more compact and efficient, in that the shape memory wires only require an electric current for movement.



    Figure 1: Typical Wing and Flap

    Figure 2: Electromechanical Actuator
    Figure 3: Hinge less shape memory alloy Flap

    The shape memory wire is used to manipulate a flexible wing surface. The wire on the bottom of the wing is shortened through the shape memory effect, while the top wire is stretched bending the edge downwards, the opposite occurs when the wing must be bent upwards. The shape memory effect is induced in the wires simply by heating them with an electric current, which is easily supplied through electrical wiring, eliminating the need for large hydraulic lines. By removing the hydraulic system, aircraft weight, maintenance costs, and repair time are all reduced. The smart wing system is currently being developed cooperatively through the Defense Advanced Researched Project Agency (DARPA, a branch of the United States Department of Defense), and Boeing.

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  8. [18]
    مهندسسسس
    مهندسسسس غير متواجد حالياً
    عضو


    تاريخ التسجيل: Sep 2007
    المشاركات: 17
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    أعتذر لأن الاشكال التوضيحيو لم تظهر و لا ادري ما هي المشكلة

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