Mehmet Sarikanat

The Mechanical Properties of γ-Methacryloxypropyltrimethoxy silane-treated Jute/Polyester Composites:

In this study, jute/polyester composites were fabricated. To improve the adhesion between jute fabric and polyester alkali-treated jute fabrics were treated with γ-methacryloxypropyltrimethoxysilane (γ-MPS). The effect of silane concentrations (0.1%, 0.3%, and 0.5%) on tensile properties, flexural properties, and interlaminar shear strength was investigated. Once jute fabrics were treated with 0.1% and 0.3% silane concentrations, the tensile properties of silane-treated jute polyester composites increased. However, when 0.5% γ-MPS was used in silane treatment, the tensile properties of jute/polyester composites decreased. 0.3% silane-treated jute/polyester composites exhibited superior improvements in terms of the flexure properties among the fabricated composites. Interlaminar shear strength measurements showed that best adhesion was provided by using 0.3% silane-treated jute/polyester composites. Good adhesion between silane-treated jute fabric and polyester was also confirmed by scanning electron microscope observations.

The Influence of Oligomeric Siloxane Concentration on the Mechanical Behaviors of Alkalized Jute/Modified Epoxy Composites:

In this study, jute fabrics/modified epoxy composites were fabricated by means of hand lay-up process. In order to enhance adhesion between the alkalized jute fabric and epoxy, modification processes was carried out by applying an oligomeric siloxane at different concentrations into epoxy matrix. The influence of resin modification processes on mechanical properties was examined. Tensile and flexural properties and interlaminar shear strength (ILSS) of the composites were measured. It was shown that the ILSS values are increased from 14.18 MPa for alkalized jute fabric/epoxy composite to 22.82 MPa for alkalized jute fabric/3% (w/w) oligomeric siloxane modified epoxy composite. The improved adhesion between the fiber and the matrix may be a result of modification of epoxy matrix with an oligomeric siloxane. This conclusion was confirmed by the morphology observations investigated by scanning electron microscopy. Besides, the modification of epoxy with 3% (w/w) oligomeric siloxane resulted in 30.4% increase in the tensile strength of alkalized jute fabric/epoxy composite. From results of the flexural modulus, application of oligomeric siloxane into epoxy matrix leads to much stiffer jute fiber—epoxy composite.

The evaluation of displacement resistance of glass FRC posts to root dentine using a thin slice push-out test

AIM To investigate and compare the displacement resistance of glass fibre reinforced composite (FRC) posts to root dentine after luting with different adhesive systems. METHODOLOGY A total of 32 noncarious extracted human mandibular premolars were prepared for post-cementation using the FRC Postec system (Ivoclar Vivadent, Schaan, Liechtenstein) and divided into four groups (n = 8). The posts in each group were luted with one or other of the following materials. Group 1: Variolink II/Excite DSC (etch-and-rinse, dual-curing), group 2: Clearfil Esthetic Cement/ED Primer II (self-etch, dual-curing), group 3: Multilink/Multilink Primer (self-etch, chemical-curing) and group 4: Multilink Sprint (self-adhesive, dual-curing). Specimens were sectioned to obtain slices with the post in the centre and with the root dentine overlaid by the autopolymerizing acrylic resin on each side. The displacement resistance was measured using a Universal Testing Machine at a crosshead speed of 0.5 mm min(-1). The displacement resistance of the specimens were calculated and expressed in MPa. Data were analysed with one-way ANOVA and post hoc Tukeys test (P < 0.05). RESULTS Mean (SD) values of displacement resistance data in MPa are as follows: group 1, 12.08 (2.13); group 2, 12.39 (2); group 3, 11.3 (1.23); group 4, 14.29 (1.84). There were statistically significant differences amongst the groups (P = 0.021). A statistically significant difference was observed for the displacement resistance values between groups 3 and 4 (P = 0.015), that is between Multilink/Multilink Primer and Multilink Sprint. CONCLUSIONS Glass FRC posts luted with self-adhesive luting system exhibited higher displacement resistance than when luted with chemical-curing self-etch luting system.

Finite-element analysis of thick composite beams and plates

In the analysis of thick composite structures by the finite-element method there are some techniques which are used to determine the material properties. In order to determine material constants of a multi-layered composite element, the most commonly used method is to take an average value for element material properties. A finite-element analysis program was developed to analyze multi-layer composite beams and plates. In addition to the arithmetic average, a new method, called the weighted average method, was developed. By considering different loading conditions, one of the averaging methods was utilized. The effects of two averaging methods on the results were investigated. The results were compared with the analytical solutions. Both methods gave matching results for certain types of loading.

The effect of argon and air plasma treatment of flax fiber on mechanical properties of reinforced polyester composite

Flax fibers were modified by argon and air atmospheric pressure plasma treatments to improve the mechanical properties of flax fiber-reinforced unsaturated polyester composites. Plasma treatments were carried out at plasma powers of 100, 200, and 300 W. Both plasma surface treatments were conducted to improve the tensile strength, tensile modulus, flexural strength, flexural modulus, interlaminar shear strength (ILSS), Mode I interlaminar fracture toughness (GIC), and Mode II interlaminar fracture toughness (GIIC). Moreover, the maximum improvement in the mechanical properties was obtained after air plasma treatment of flax fiber at a plasma power of 300 W. Tensile strength, flexural strength, ILSS, GIC, and GIIC values of flax fiber-reinforced polyester composites increased by nearly 34%, 31%, 39%, 35%, and 42%, respectively. However, for argon plasma-treated flax fiber-reinforced polyester composites, the mechanical properties of composite increased up to argon plasma power of 200 W.

Variations of mechanical properties of jute/polyester composite aged in various media

Woven roving jute fiber-reinforced unsaturated polyester composites were subjected to water absorption tests in order to study the effects of water ageing on the mechanical properties. Composite specimens were immersed in distilled water and salt water up to 2736 h. The water absorption of specimens reached to an equilibrium level after an immersion time of 300 h. It was observed that tensile, flexural, and interlaminar shear strengths (ILSSs) of jute/polyester composites decreased depending on the immersion time. The ILSS values of the composites were reduced by more than 53% for both the distilled water and the salt water after an immersion time of 2736 h.

Effect of siloxane treatment of jute fabric on the mechanical and thermal properties of jute/HDPE

The mechanical and thermal properties of jute fiber/HDPE composites as a function of alkali and oligomeric siloxane treatment of jute fabric were investigated. The effect of surface treatments on the composites was assessed by means of tensile test, short-beam shear test, three-point bending test, SEM, TGA, and DSC. When jute fabric are first treated with alkali solution and then oligomeric siloxane solution, 34% and 49% increases in tensile and flexural strength were observed, respectively. Moreover, it is interesting to note that after alkali and siloxane treatment of jute fabric, 169% increase in ILSS of jute/HDPE composite was obtained. This demonstrates that the adhesion between jute fiber and HDPE matrix is greatly increased by alkali and oligomeric siloxane treatment of jute fabric. This observation was also confirmed by SEM analysis of fracture surface of composites. Alkali and oligomeric siloxane treatment of jute fabric did not considerably change thermal stability and melting and crystallization temperatures of jute/HDPE.

Determination of bone density distribution in proximal femur by using the 3D orthotropic bone adaptation model

Most of the models developed and presented in the literature about bone remodelling assume bone as isotropic material. During this study, a structural model which has orthotropic bone properties is developed to simulate bone behaviour under mechanical loads. For a three-dimensional finite element modelling of proximal femoral bone, a computer code was written to investigate bone property changes owing to mechanical loads. The bone density distribution was determined after stress analysis was carried out in an iterative method. At every time step the bone properties were calculated depending on density change. Additionally, the effects of the bone remodelling parameters and sensors on numerical results were investigated. The most realistic bone density distribution in the proximal femur is obtained with strain energy density sensor. Generally initial bone density values do not have any effect on density distribution but at the low iteration numbers they may have some effects. Lastly, the density distribution of proximal femoral bone is more realistic for the dead zone size less than 0.35 and the stimulus value less than 2500.

Buckling Analysis of Laminated Composite Circular Plates with Holes

In this study, buckling analysis of laminated composite circular plates having circular holes and subjected to uniform radial load is investigated by using the finite element method. The effects of hole sizes, location of the holes, thickness variations and boundary conditions on the critical buckling load, and the buckling mode shapes of the composite plates are determined. Eight node isoparametric shell elements with 24 degrees of freedom are used during the investigation.

Mechanical anisotropy in unidirectional glass fabric reinforced oligomeric siloxane modified polyester composites

In this study, the effect of incorporation of oligomeric siloxane into unsaturated polyester on mechanical behavior of unidirectional glass fiber/polyester composites has been investigated by means of tensile, flexural and short beam shear tests. The amount of oligomeric siloxane added into unsaturated polyester was in the range 1–3 % by weight of the glass fabrics. Mechanical tests were conducted at different angles (0 °, 45 °, and 90 °) with respect to fiber direction. The higher siloxane content exhibited a tendency to have greater tensile, flexural and interlaminar shear strength values in machine direction, bias direction and cross direction. From Scanning electron microscopy images, the presence of polyester particles on the unidirectional glass fiber surface confirmed better adhesion.