Ömer Sinan Şahin

Enhancement of Wear and Friction Characteristics of Epoxy Resin by Multiwalled Carbon Nanotube and Boron Nitride Nanoparticles

Epoxy resins are widely used in engineering applications. However, their low thermal stability limits their usage at high sliding velocities and loads. The mechanical properties and thermal stability of a machine element subjected to friction and wear are very important. In this study, friction and tribology behaviors of multiwalled carbon nanotubes (MWCNTs) and boron nitride (BN)-modified epoxy resin have been investigated. Epoxy resin modified by three different nanoparticle configurations, 0.3% MWCNT, 0.5% BN, and 0.5% MWCNT/0.3% BN, was investigated. The tribological characteristics of nanoparticle-modified epoxy resin were compared with properties of neat resin. The friction and tribological behavior of modified epoxy resin were tested using a ball-on-disc test stand at 1.2 and 1.5 ms−1 sliding velocities under 10 N applied load. The tests were done under dry condition and 1,800 m distance. The friction coefficient, wear loss, and temperature increase during testing were recorded and compared with that obtained for neat epoxy. It is observed that nanoparticle modification resulted in enhanced wear resistance and a reduction in friction coefficient and working temperatures.

Investigation of Wear Performance of Canola Oil Containing Boric Acid under Boundary Friction Condition

The aim of this study is to investigate the tribological behaviors of pure canola oil and 5% boric acid–added canola oil after unexpected oil drainage. Tests were performed under 0.6 m/s sliding velocity and 80 N contact force using a pin-on-disc test stand. Tests were started with full lubrication and continued for 800 m. After that the oil was drained from the oil tank and the system was run for 10,000 m without lubrication. The variation of friction coefficient, contact temperature, and wear was compared for pure and boric acid–added oil. It was observed that boric acid–added oil can continue lubricating even after oil was drained from the tank.

Using artificial neural networks for real-time observation of the endurance state of a steel specimen under loading

The surface temperature behavior of a steel specimen under bending fatigue is exactly divided into three stages: an initial temperature increase stage, a constant temperature stage and an abrupt temperature increase stage at the end of which the specimen fails. To obtain the endurance state of the specimen we use its thermal images (TIs). By applying artificial neural networks (ANNs) and other operations to these TIs we obtain spots with maximal, approximately medium and minimal temperatures. Then by using these temperatures we analytically obtain the temperatures all of spots of the specimen and localize the regions consisting of spots of relatively high temperatures. We consider such a region as one to be cracked firstly. This approach allows us to handle only those spots that are of interest and to work in real-time even by using an infrared (IR) camera and a computer with average technical features. We are using the result obtained in this study for fatigue testing the steel materials and for sensing the pre-fatigue state of a specific part of a machine being worked in order to take preventive measures before it breaks down.

Low-velocity impact behavior of carbon fiber/epoxy multiscale hybrid nanocomposites reinforced with multiwalled carbon nanotubes and boron nitride nanoplates

In this article, the mechanical properties and dynamic response of hybrid filler-modified epoxy/carbon fiber multiscale composites were investigated. The hybrid fillers composed of multiwalled carbon nanotubes and boron nitride nanoplates were dispersed in epoxy resin and used as matrix material. The multiscale hybrid laminated composites were stacked symmetrically consisting of 10 plies of woven carbon fibers and fabricated by vacuum infusion technique. The mechanical properties of the hybrid composites were investigated by tensile tests. Impact response and energy absorption capacity were investigated by using weight drop test method and the tests were performed according to ASTM-D-7136 standard with impact energies of 5, 10, and 15 J. The impact force and displacement versus interaction time were measured. The impulsive force, energy absorption capability, and damage formation were also investigated. It is observed that when the resin is modified by nanoparticles, both strength and the % strain at fracture increase considerably. However, it is shown in the subject manuscript that the enhancement of mechanical has not fully transferred to dynamic response and energy absorption capacities of nanocomposites.

Enhancement of flexural and shear properties of carbon fiber/epoxy hybrid nanocomposites by boron nitride nano particles and carbon nano tube modification

In this study, the effect of boron nitride nano particle (BNNP) and/or carbon nanotube (CNT) adding for epoxy modification upon tensile, flexural and shear properties of epoxy resin and carbon fiber (CF) laminated nanocomposites were investigated. Epoxy based polymer nanocomposites were prepared by conventional casting in stainless steel mold and the CF/epoxy laminated nanocomposites were produced via vacuum assisted resin transfer molding (VARTM). Experimental results showed that the tensile, shear and flexural properties of epoxy nanocomposites and CF/epoxy laminated nanocomposites considerably increased by adding nanoparticle. Scanning electron microscopy (SEM) was utilized in order to determine damage formation of experimented nanocomposite samples. The results of laboratory tests showed that the highest values of mechanical properties were obtained for BNNP-CNT hybrid nanocomposite specimens. Bending stiffness increasement values of BNNP-CNT/Epoxy and BNNP-CNT-Epoxy/CF achieved by 27.5 %, and 38.5 %, respectively. Shear strength increasement for BNNP-CNT/Epoxy and BNNP-CNT-Epoxy/CF were determined by 23 %, and 90 %, respectively.

Effects of Production Parameters and Conditioning upon Ballistic Characteristics of Para Aramid Light Armors

Composite materials are increasingly used in armors design due to their high strength to weight ratios and energy absorption capacities. It is very important to determine the best production parameters for armor production. On the other hand, the armors must show superior durability against harsh working conditions. So it is crucial to know the ballistic characteristics of such composite armors. In this study the effect of production parameters upon the terminal ballistic properties of para-aramid composite armor were examined under different conditionings. The composite armor plates were produced by hot pressing with four different pressing times. Before ballistic test, the armor plates conditioned at +21, +63, and -35°C at 50% of relative humidity and +21°C immersed into water temperature for 24h, in which weapons, ammunition, and equipment designed for use in the battlefield, are expected to fully operate.

Thermal stability and adhesive strength of boron nitride nano platelets and carbon nano tube modified adhesives

The effect of multi-walled carbon nanotube and/or boron nitride nano platelets usage on shear strength and thermal stability of epoxy based adhesives have been investigated. Commercially available diglycidyl ether of bisphenol A based epoxy was used as matrix and reinforced by using nanofillers. The resulting adhesive was tested for its shear-lap adhesion to aluminum alloy sheets (2024-T3). The nano particles modified epoxy adhesives were characterized by Fourier transform infrared, differential scanning calorimetry, and thermal gravity analyses analysis. These characterizations revealed that incorporation of nano particles can result in enhancement in chemical stability. Single lap strength joint testing was conducted in accordance with ASTM-D-1002-10 standard. Fracture morphologies and the effects of multi-walled carbon nanotubes and boron nitride nano platelets on epoxy adhesive were investigated after shear tests by means of scanning electron microscopy. Compared to neat epoxy, increases of 30% in shear strength and 57% in energy required to break joints have been obtained by multi-walled carbon nanotube/boron nitride nano platelet modification.

Investigation of Bending Fatigue of Composite Plates by Using Infrared Thermography

In this study, the temperature rise of composite plates with a hole during fatigue loading was investigated. Woven glass/epoxy composite plates with eight plies were subjected to bending fatigue loading and materials were observed by using a thermal camera during the test. Previous works showed that a heat generation can form due to internal friction and damage formation. Therefore, a thermographic infrared imaging system was used to detect the temperature rise of composite specimens. During the tests, the thermal images of the specimens have been recorded by a thermal camera and then transferred to the image processing program which has been developed by using MATLAB. By using these thermal images, the spot temperatures of the specimen were obtained by using artificial neural networks. The obtained temperatures show local increase at places where the heat generation localized. These regions considered being the probable damage initiation sites. It is shown in this study that most probable damage initiation zones in the woven glass/epoxy composite material can be detected by using infrared thermography (IRT) approach prior to failure.

Plastic Zones and Residual Stresses of Metal Reinforced Composite Laminated Rectangular Plates with a Hole under In-Plane Loading

The nonlinear stress analysis and the spread of plastic zones in layered woven steel fiber-reinforced thermoplastic-matrix laminated rectangular plates are examined using the Finite element method and the first-order shear deformation theory for small deformations. Composite structures consisting of woven Cr–Ni wire as the fiber and F2.12 low-density polyethylene as the thermoplastic matrix are manufactured by hot-press molding. The mechanical properties are experimentally determined. The effect of aspect ratio of rectangular plate and antisymmetric structure is investigated. It is assumed that the laminated plates are subjected to in-plane uniform loads. Loading is gradually increased from the yield point of the plate as 0.01MPa at each load step. Load steps are chosen as 300, 350, and 400 iterations. Residual stresses and expansion of plastic zone have been presented by means of tables and figures.

Mechanical properties and microstructure of composites produced by recycling metal chips

In this study, the processing and mechanical properties of porous metal matrix composites (MMCs) composed of spheroidal cast iron chips (GGG40) and bronze chips (CuSn10) and formed by hot isostatic pressing were investigated. Bronze chips (CuSn10) were used as a matrix component, and spheroidal cast iron (GGG40) chips were used as a reinforcement component. The MMCs were produced with different CuSn10 contents (90wt%, 80wt%, 70wt%, and 60wt%). The hot isostatic pressing process was performed under three different pressures and temperatures. The produced MMCs were characterized using density tests, Brinell hardness tests, and compression tests. In addition, the consolidation mechanism was investigated by X-ray diffraction (XRD) analysis and scanning electron microscopy. The test results were compared with those for bulk CuSn10 and bulk GGG40. Mechanical tests results revealed that the metallic chips can be recycled by using hot pressing and that the mechanical properties of the produced MMCs were similar to those of bulk CuSn10. XRD and microscopy studies showed that no intermetallic compounds formed between the metallic chips. The results showed that the CuSn10 and GGG40 chips were consolidated by mechanical interlocking.