Iraqi journal of mechanical and material engineering

This paper provides six tests were carried out for the base alloy (BA) (Al 2%Mg) and the three composite samples ((A1 (Al- 2%Mg-2%CKD), AR2R (Al-2%Mg-8%CKD) & AR3R
(Al-2%Mg-16% CKD))) which were prepared by using powder metallurgy technique. As a
results, it was found an optimum composite material using the hybrid method represented by
genetic algorithms by using through carry out two ways of crossover (1X, 2X), basing on
statistical data obtained from experimental results. The basic data were built, depending on
their properties, to describe the composite. Then, the evolution algorithm is to make
procedure for the genetic clustering process and provides a number of required clusters; to
avoid the overlapping between clusters with the other. One of the clustering validity
measures called "Davies-Bouldin index" as fitness function of that algorithm that used.
Then, the two types of properties for each cluster: mechanical properties (hardness, thermal
conductivity, wear rate, friction coefficient) and machining properties (surface roughness,
tool life) were extracted. This paper concludes that composite (43&33) represented optimum
composite material by using one point and two point crossover operators (1X,2X)
respectively.

In this paper, the effect of different types of stiffeners on the cylindrical shell structure is presented. The stiffened shell models are examined under the action of static and dynamic excitations. Finite element models for the different stiffened cylindrical steel shell have been created by considering the helix angles and height of stiffeners, and a cantilever supported models are used. Additionally, the models are assumed to have a constant mass which is (4 kg) . All structure models have examined under action of static, harmonic and transient loads. Also the dynamic properties (natural frequencies) are computed for each FEMs. A concentrated load of the magnitude of (100 N) in three directions (x, y and z) is used in these structural analyses (static, harmonic and transient). This force is applying to the upper edge which is opposite the clamping edge . From these analyses, the best helix angle occurs at stiffener angle (90o), and the best height of stiffener that the modal analysis gives is (2 cm) and that gives by other analysis is (6.25 cm) . Finally, a comparison between experimental work of [M. Bagheri. and A. A. Jafari(2006)] and numerical part of the current paper has been occurred with a small percentage error between them.

The objectives of this article is to study performance of solar nanofluid heating system when metal(Cu(30nm) +DW) and titanium oxide (TiO2(50nm) +DW) nanofluids was taken as the working fluid as well as the effect of nanoparticles on solar nanofluid heating system. With higher thermal conductivity of the working fluid the solar collector performance could be enhanced compared with that of distilled water. The two types of nanoparticles are used in the investigation with four particles concentration ratios (i.e. 0, 1, 3 and 5 % vol), mass flow rate (30,60 and 90 lit/hr m2) and the based working fluid was distilled water. The effect of different nanoparticle concentrations of Cu and TiO2 mixed with distilled water as base fluid was examined on solar collector efficiency for different mass flow rates (30, and 90 lit/hr m2). The area under the curve as an index was used for comparing the effects of mass flow rates and nanoparticle concentrations on the collector total efficiency. ASHRAE 93 was used to test the solar collector. The experimental results indicated that the concentration at 1%vol showed insignificant results compared with distilled water. As well as The nanofluids (Cu + DW), at concentrations 5%vol and mass flow rates (30, and 90 lit/hr m2), the thermal solar characteristics values of FR(ôل), – F RUL were 0.581, 10.145W/m2.K, 0.676 and 10.907 W/m2.K, while the nanofluid (TiO2 + DW) 0.482,9.093 W/m2.k ,0.567 and 9.539 W/m2.K respectively. Whereas in the case of distilled water at mass flow rates 30 lit/hr m2 and 90 lit/hr m2 were 0.449,8.013 W/mP
2
P.K,0.504 and ,8.101 W/mP
2
P.K respectively. Moreover use of
nanofluids (Cu (30nm) +DW) and (TiOR2R (50nm) +DW) as a working fluid could improve
thermal performance of evacuated tube solar collector compared with distilled water,
especially at high inlet temperature. The solar collector efficiency for nanofluid (Cu (30nm)
+DW) was greater than nanofluid (TiOR2R (50nm) +DW) due to small particle size for the
cupper compared with titanium oxide as well as high thermal conductivity for silver. The
type of nanofluid is a key factor for heat transfer enhancement, and improve performance of
flat plate solar collector.

In the present search, attempts are made to develop the properties of PMMA resin that used for upper and lower prosthesis complete denture, by addition two different types of particles, which included: nano-hydroxyapatite (nHA) particles and micro-zirconia (ZrO2) particles that added with different volume fractions of (1%, 2% and 3%) to poly methyl methacrylate (PMMA) cold cured resin as new fluid resin matrix. Also woven glass fiber kind (E-glass) and woven Kevlar fiber kind (49), it were added with a fixed volume fraction of (5%) to PMMA composites. In this work the composite prosthetic dentures specimens preparation was done by using (Hand Lay-Up) method as six groups which includes: the first group consists of PMMA resin reinforced by nHA particles, the second group consists of PMMA resin reinforced by ZrO2 particles, the third group consists of (PMMA-nHA) and glass fiber layer as laminated composite , the fourth group consists of (PMMA-ZrO2) and glass fiber layer, the fifth group consists of (PMMA-nHA) and Kevlar fiber layer and the sixth group consists of (PMMA-ZrO2) and Kevlar fiber layer.
The experimental part of this study included performing many mechanical tests which, includes (Flexural, Maximum Shear Stress and Impact) tests. The result of this study showed the values of most properties increased with increasing of the volume fraction of (nHA and ZrO2) particles in polymer composite materials. While, the impact strength decreased. The ZrO2 particle and woven mat Kevlar fiber had shown greater values for the most composite materials properties for all groups’ specimens except the flexural strain.
Also the results showed the maximum values for hybrid laminated composite properties (flexural modulus and impact strength) were obtained in hybrid laminated composite materials for sixth group specimens. While, the maximum value for properties (flexural strength and max shear stress) were obtained in hybrid laminated composite materials for fourth group specimens.

This work deals with a study of the effect of natural fibers -epoxy composite on damping .Palm fiber was used in this investigation. Four blocks of dimensions (10X20)cm were prepared using epoxy-resin and palm fiber by volume fractions ratio of (0%,4%,8%,16%). After preparation of the composite material some of mechanical properties of prepared samples were studied. The specimens were cut from the blocks and tested in the scleroscope system by using a 50g steel ball on specimens released from a height of 70 cm. The vibration signal was obtained by the accelerometer and fed to the oscilloscope .The oscilloscope output signal was analyzed using logarithmic decrement method, to obtain the damping ratio. The effect of three testing temperatures (-30,25,65)Co was checked. It was observed that the damping ratio decreases by 24.4% with increasing volume fraction of reinforcement materials at temperature 25Co. While at temperature 65Co this ratio reached 53% and at temperature (-30)Co the ratio reached 31.25%. The results showed that using a filler of natural fiber will decrease the damping ratio as compared with 0% volume fraction specimen. While the effect of testing temperature (-30,25,65)Co on the damping ratio with deferent volume fractions showed an increase in percentage of damping ratio as temperature increased and volume fraction increased. These result were compared to the another composite material used glass fiber and carbon fiber for the same author which found that the percentage of و for palm fiber increased up to 40%when used glass fiber and 46% in the case of use carbon fiber.

Selection the appropriate and optimum maintenance policy at any industrial plants is one of the important decisions that impact on competitive advantage which requires the study of all the factors surrounding the maintenance and discuss the results. decision-making between the implementation of the police of preventive or emergence maintenance in industrial company on several factors such the type of product and production quantity and the use of the product and machines age and the cost, maintenance of the machine and equipment during the specified period of time. The types of maintenance can be divided into two main types: preventive maintenance &Emergence Maintenance.
The aim of the research is use probabilistic model to determine the optimum maintenance policy and deciding when to maintenance, through an economic comparison between the costs of preventive & Emergence maintenance that based on:- 1-probability of Breakdown during periods of time.
2-Repeat the Breakdown during previous period’s time.
The Researcher used MS-Excel program in building a probabilistic model to solve this problem& apply Practical application at the General Company for Leather Industries at men\'s shoe manufacturing plant (the production line (7)) .we found preventive maintenance is most economic police rather than emergence police.