A-H. I. Mourad

On use of trilayer low density polyethylene greenhouse cover as substitute for monolayer cover

Abstract Few attempts are available in the literature on utilising the trilayer low density polyethylene (LDPE) film as new generation of greenhouse cover to substitute the monolayer film that is often used. This paper investigates and compares the degradation behaviour and durability of both covers. The covers are exposed to 7 months of natural withering. The results revealed that the degradation resistance of trilayer film is better than the monolayer film in terms of their mechanical and optical properties. The service lifespan, based on 50% reduction in the property criterion, of the trilayer film is found to be double the service lifespan of the monolayer film.

The effect of sand wind, temperature and exposure time on tri-layer polyethylene film used as greenhouse roof

This work aims at studying the degradable effect of artificial ageing on tri-layer stabilised low-density polyethylene (PE) films used as greenhouse cover in the North Africa environment. The film was supplied by Agrofilm company, Algeria. Colour additives and infra-red and ultraviolet stabilisers were used. Optical, thermal, surface and mechanical properties have been investigated for virgin sample and samples exposed to sand wind for different exposure periods (1, 2, 4 and 8 h) of artificial ageing at a temperature of 40°C simulating Saharan environment. The findings of this study show that the harsh environmental conditions of exposure to temperature and sand wind have significant degradable effects on the properties of the PE film. The transmission of the film and its mechanical properties have reduced significantly due to exposure to sand wind and temperature. The study revealed also that the degradation parameters measured are directly related to the criteria for evaluating the effectiveness of agricultural greenhouse.

Establishment of a three‐dimensional culture system of gastric stem cells supporting mucous cell differentiation using microfibrous polycaprolactone scaffolds

To generate various polycaprolactone (PCL) scaffolds and test their suitability for growth and differentiation of immortalized mouse gastric stem (mGS) cells.

Multilayers Polyethylene Film for Crop Protection in Harsh Climatic Conditions

In this work the performance and durability of a new generation of greenhouse covers, in which the cover is composed of five layers, are investigated. A sand wind ageing was performed under different exposure conditions. Surface morphology and chemical, physical, and thermal characteristics were investigated by using optical microscopy, FTIR, and tensile test techniques. In addition, the mechanical integrity of the five-layer film was assessed. The analysis indicated that the sand wind treatments have a significant influence only on the performance of the film. An attempt has been done to compare the properties of the five-layer film with the monolayer and trilayer films with or without air bubble under similar conditions. The results revealed that the five-layer film proved to be a promising greenhouse covering film.

Novel Technique for Normalizing Load–Displacement Curves in Fracture Testing

Fracture experiments conducted as part of research on stable crack behavior in low alloy steel (EN 34NiCrMo6) are analyzed and presented. CT specimens of low constraint (section slenderness ratio, b0/B ∼ 6), with various crack depth and different loading angles, ϕ, were investigated. Analysis of the load displacement curves revealed that the initiation load is found to be the same when normalized to the maximum load, Pmax. The load-line displacement ΔLL at Pmax (ΔPmax) was also found to have a single value. Hence the load displacement curves were presented as a unique normalized P–ΔLL curve. These normalized curves demonstrate having a single “representative/trend” curve that characterises the stable crack growth behavior. The proposed normalization technique was also applied to additional literature data on different materials with various specimen configurations and loading modes with success. This technique could also be useful in studying the fracture of low constraint specimens and contributing to the transferability issue for structural application.

Fracture Assessment of X65 Steel Pipe With Through-Wall Crack Under Pure Bending

Stable crack growth emanated from circumferential through-wall crack in X65 steel pipe under pure bending was evaluated. Seamless carbon steel pipes grade X65 PL5 with an inner diameter of 42.9 mm and an outer diameter of 60.3 mm were used in the present experimental work. This type of pipes is of common use in piping systems of gas and oil industry. Pipes of different circumferential crack depths were tested. J-R curve was used to characterize the nonlinear fracture behavior of the through-wall crack pipe. Variation of J with crack growth, crack surface area and deflection of the pipe were obtained. J-integral-crack growth curve was used in the calculation of critical crack size based on the Jc value measured in our previous experimental work by testing full scale pipe made from the same material. The length of crack at unstable crack growth is also determined. Both critical and instability crack sizes can be used for fracture assessment of X65 steel pipes.Copyright

Fracture Toughness Determined From Full-Scale Pipe

Fracture toughness for full scale steel pipe of API 5L grade X65 PSL1 (ASTM A694F65) medium strength grade pipeline steel has been measured by a new test specimen utilizing the same procedure of the standard test methods ASTM E 399-90 and E 1820-01. Full scale pipe with circumferentially machined notch is pulled axially by tensile load up to fracture. An external circumferential sharp notch has been machined in the wall of the pipe to simulate the crack. To insure a plane strain condition around the crack a well lubricated and axially free loaded plug has been mounted, symmetrically around the circumferential notch, inside the pipe. Evidences of cleavage fracture have been observed on the fracture surface. The measured value of the fracture toughness has been found to be very close to the values measured according to the standard test for steel plates of similar grade. The new proposed testing method for full scale pipe can be used regardless its dimensions since it appears to provide plane strain condition around the crack.Copyright

Mixed Mode Failure Criterion for Random Composites Using a Finite Element Model

In this research mixed-mode fracture behaviour of glass fibre/epoxy composite with randomly distributed glass fibres investigated. Various modes of loading were applied. Compact tension shear (CTS) fixture with different loading angles were used. The testing is used to measure the fracture toughness. Critical strain energy release rate (CSERR) of the composite was then calculated using the measured fracture toughness. A model is proposed to predict the value of CSERR based on the constituents and interfacial properties. Different failure mechanisms are considered in developing a criterion. To derive the criterion a FE model is used to determine the amount of energy released during the fibre pull out which is major part of energy dissipation.

Fracture Toughness Measurements From Circumferentially-Notched Pipes Tests

Fracture toughness for full scale steel pipe of API 5L grade X65 PSL1 (ASTM A694) medium strength grade pipeline steel has been measured by a new test specimen utilizing the same procedures of the standard test methods ASTM E399-90 and ASTM E1820-01. Full scale pipe sections with circumferentially machined notches were pulled axially by tensile loads until fracture. An external circumferential sharp notch was machined in the wall of the pipe to simulate the crack. In addition to testing a plain pipe, a well lubricated and axially free loaded plug was mounted inside the pipe to provide plane strain condition for notch failure. Ductile dimple fracture was observed on fractured surfaces of plain pipes, while evidences of cleavage fractures have been observed when the internal plug was used. The measured value of the fracture toughness has been found to be in good agreement with the values measured according to the standard tests for steel plates of similar grade and with the with those measured using in situ Automated Ball Indentation (ABI) tests conducted on the same pipe section. The new testing method for full scale pipe can be used regardless of pipe dimensions since it appears to provide plane strain conditions around the crack.

Study on the Mechanical Behavior of Aluminum Alloy 5083 Friction Stir Welded Joint

The mechanical behavior of friction stir welded joints made of aluminum alloy 5083-H111 was studied in this investigation. Different welding processes parameters (rotational speeds, travelling speeds and tool pin shapes) were used to investigate the effect of process parameters on the strength and fracture properties of the joint. Scanning electron microscopy and optical microscopy analysis were conducted to study the effect of friction stir welding FSW process on the grain size in the welding zones. In general, the results illustrated that tool profile, the rotation speed and the traveling speed has great effect on the strength of the welded joint. Scanning electron microscopy and optical microscopy investigations showed that the grains inside the welding zone was refined and equiaxed resulting in higher hardness inside the nugget.© 2014 ASME