Using Ultrasonic Wave to Study Modulus of Elasticity, Shear Modulus and Poissons's Ratio of Polymer Concrete.

The main aim of this study is assess the modulus of elasticity , shear modulus and Poissons's ratio of polymer concrete (PC).Polymer concrete is a composite material realized with resin and aggregates.The Unsaturated polyester composite  resin was used for binding the aggregates. The silica foam and  glass fibers were introduced in the composition as filler.Some mechanical properties of polymer concrete have been investigated, by non-destructive method. The experimental results of ultrasonic wave at 26 KHz test were correlated with, modulus of elasticity, shear modulus and Poissons's ratio. The fiber percentage and silica foam was constant, the unsaturated polyester resin and the Silica sand dosages were varied.The results showed that by increase the percentage of sand aggregate (%W) in all groups the Poissons's ratio,Pulse Velocity,Modulus of Elasticity and Shear Modulus are increased. Keywords: Shear Modulus, Polymer Concrete, Modulus of Elasticity, Poissons's ratio,Ultrasonic wave

Experimental and Numerical Evaluation of the Fundamental Natural ‎Frequency of a Spherical Core Sandwich Structure.‎

  مقدمة: الهدف من هذه الدراسة هو التحقق من تأثير متغيرات العوامل الجيومترية عدديا وتجريبيا على خاصية التردد الطبيعي لألواح ساندويج ذات قلب كروي . هذه الالواح مصنعة بطريقة أبتكارية بواسطة أستخدام شمع النحت التعليمي . العوامل الجيومترية هي قطر الكرة وسمك الوجه والمسافة بين الكرات. طرق العمل: طبقا لمنهجية استجابة السطوح - تصميم التجارب تم تصميم 15 عينة وفق طريقة بوكس-بيهنكن  وأعتمادا على الظروف التجريبية لحدود قيم كل متغير. المادة الأساس في الصب هي البوليستر الغير مشبع . الطول الفعال لجميع العينات المصنعة كان ثابتا بقيمة 20 سم. تم تقييم التردد الطبيعي عدديا باستخدام نظرية العناصر المحددة وعمليا باستخدام الاختبار المشروط  وحساب الفارق بينهما. تأثير المتغيرات الجيومترية تم تحليلها بأستخدام نظرية تحليل التباين الإحصائية. الأستنتاجات: بينت هذه الدراسة فهما جيدا لتأثير المتغيرات الجيومترية لألواح ساندويج ذات قلب كروي عل خاصية التردد الطبيعي. النتائج العملية والعددية بينت  فارقا في القيم لم يتجاوز 15% أما النتائج الإحصائية فبينت ان المسافة بين الكرات كان لها تاثير كبير جدا ورئيسي على جميع المتغيرات الجيومترية الأخرى. سمك الوجه وقطر الكرة كان لهما تاثير أقل وفقا الى تلك البيانات.Background: This study investigates the effect of the variation of the geometrical factors on the fundamental natural frequency of the novel spherical core sandwich structure numerically and experimentally.  These novel structure are made up by using carving wax. The geometrical factors are diameter of sphere, skin thickness and spacing between spheres. Materials and Methods: Fifteen specimens according to response surface methodology - design of experiments  and using Box-Behnken method were manufactured from unsaturated polyester material with different geometry while maintaining a 20 cm effective length. The fundamental natural frequency was evaluated according to two methods numerically by using finite element analysis and experimentally by using the modal test. ANOVA statistical analysis was used to evaluate the effect of the geometrical factors on the natural frequency Results: The results show that the discrepancy between these methods was less than 15%. The spacing between the spheres was a dominant factor that influence the fundamental natural frequency. The sphere diameter is a less dominant factor while the skin thickness has a minor influence on the fundamental natural frequency of the spherical core sandwich structure. Conclusions: This study provides a better understanding of the influence of the geometrical properties of the structure on the fundamental natural frequency. The most influential factor on the fundamental natural frequency is the spacing between the spheres while The diameter of the sphere has less influence, while the skin thickness has a minor effect on the fundamental natural frequency

RICE HUSK ASH AS A NANO-FILLER TO SYNTHESIZE THERMOSETTING POLYMER NANOCOMPOSITES AND EVALUATION OF ITS TRIBOLOGICAL BEHAVIOR

This paper deals with synthesizing of nanocomposites of unsaturated polyester (UP) filled with nano silica and investigation the effect of silica content on the tribological behavior of UP and nanocomposites . Silica nanoparticles were prepared by burning rice husk ash (RHA) as an agricultural waste material. Three different percentages as 2%, 6% and 10% of nano silica were added to the unsaturated polyester and dispersed by using ultrasonic waves method. As a result of agglomeration and sedimentation of nano RHA particles, dispersing by ultrasonic waves was very effective to terminate these challenges. X-Rays diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and scanning electron microscopy (SEM) technics were used for characterization of materials. RHA-UP nanocomposites were tested for their tribo-performance by pin-on-disc machine. XRD demonstrated that white rice husk ash consists of amorphous silica. SEM demonstrated that silica particles were distributed uniformly and well embedded within the polyester matrix. Results showed an improvement in wear resistance with relatively stable friction coefficient with the addition of 10% nano silica. Adding 2 wt% nano RHA negatively affected the wear resistance of RHA-UP nanocomposite .The best tribological performance of 10% RHA-UP nanocomposites achieved at load 10N. Incorporation of RHA with unsaturated polyester has advantages of reducing pollution, making the pollutant RHA as a valuable material to produce low cost and lightweight products with modified properties. Silica enriched RHA could prove to be cheaper anti-wear additives for producing high performance unsaturated polyester composites such as brake pads