Pehlivan, Levent; Baykasoğlu, Cengiz

The experimental investigation on the compressive response of carbon fiber reinforced polymer (CFRP) honeycombs with various cell configurations was carried out in the present work. The CFRP honeycomb specimens were manufactured by corrugation technique, in which the prepreg CFRP sheets were first corrugated into the certain shape using corrugated aluminum moulds under heat and pressure, and then the corrugated CFRP sheets were glued and stacked to construct honeycomb specimens. Twenty-seven groups of specimens were experimentally tested to examine the effects of cell geometry (i.e., square, circular, and hexagonal), cell wall thickness and height on the quasi-static out-of-plane crushing performance of the honeycombs. The square, circular, and hexagonal honeycomb specimen groups were designed to have almost the same weights. The results showed that the cell wall thickness is an significant parameters on the overal crushing response of the CFRP honeycombs while the out-of-plane compressive strenght of the honeycombs is generally independent of the height. It is observed that the hexagonal specimen groups have generally superior crushing performance in comparison with the square and circular counterparts due to their large double foil bonding surfaces. The experimental results also revealed that the crushing properties of the honeycomb structures with the core densities of 157–282 kg/m 3 could be increased more than two times with the appropriate selection of cell configurations.

AtıfScopus134·WoS110·OpenAlex122

İncele

Bolat, Hakan; Şimşek, Osman; Çullu, Mustafa; Durmuş, Gökhan; Can, Ömer

Attempts to find a construction material having increased strength, ductility, toughness, and durability have led to interest in high performance fiber reinforced concrete. The use of such materials increases day by day. When the fibers are distributed in a homogeneous way and used in appropriate quantity inside the concrete, they reduce cracks, contribute to tensile strength, toughness, ductility and durability, and improve other mechanical properties. In this study, four types of concrete were produced: steel fiber (SFRC), polyester fiber (PYFRC), polypropylene fiber (PPFRC) reinforced concrete and a reference sample made of plain concrete (R1); these were then compared to one another. The ratio of fibers was used 4.25% of volume of concrete. The effects of the different types of fiber on hardened concrete were determined by conducting physical and mechanical experiments. Compressive strength, surface hardness, ultrasonic pulse velocity, carbonation, abrasion, capillarity and freeze-thaw resistance experiments were conducted on hardened concretes. SFRC had higher 12.4%, PYFRC 3.4% higher and PPFRC 4.3% lower compressive strength with respect to R1. PPFRC showed 8.04% higher compressive strength than R1 when it was determined by the surface hardness method. SFRC showed 5.4% higher compressive strength than R1 when we applied the ultrasonic pulse velocity method. In the abrasion experiment, the highest abrasion was found in SFRC with ∼0.5%, while the lowest was found in PPFRC at ∼0.18%. The highest and lowest amount of capillary water absorption was seen in R1 and PYFRC, respectively. In a carbonation experiment, SFRC was determined ∼130.8% higher than R1. It was concluded that the types of fiber used for reinforcement influenced the physical and mechanical properties of the concrete.

AtıfScopus137·WoS123·OpenAlex147

İncele

Çavdar, Ahmet

Fibers are used for improving some properties of conventional concrete (which is a brittle material) such as tensile strength, abrasion resistance, absorption and crack control. This study investigates the usability of fibers against the harmful effects of freeze-thaw cycles on cement mortars. For this objective, five different types of fibers, i.e., Polypropylene (PP), Carbon (CF), Aramid (AR), Glass (GF) and Poly vinyl alcohol (PVA) in four different ratios (0.0%, 0.4%, 0.8% and 1.2%) were added to cement mortars along with an amount of air agent. These samples were then subjected to five different freeze-thaw cycles (0, 25, 50, 75 and 100). Thus, mechanical behaviors were investigated under freeze-thaw effects. The most important results of the study are summarized; the fibers increase flexural strength and deflection ability of the samples while decreasing compressive strength, dynamic modulus of elasticity and specific mass. The highest flexural strength was obtained with a 1.2% addition of CF fiber for the samples in normal conditions. The mechanical properties of the samples subjected to repetitive freeze-thaw cycles were also investigated; the best flexural strength was provided with 1.2% CF addition, while the highest dynamic modulus of elasticity was obtained with a 1.2% PP addition.

AtıfScopus123·WoS103·OpenAlex122

İncele

Akpinar, Salih; Doru, Muhammet Onur; Özel, Adnan; Aydin, Murat Demir; Jahanpasand, Hamed Ghaffarzadeh

The mechanical behaviors of an adhesively bonded single lap joint with a spew fillet under bending moment, where the widths of the upper-adherend and lower-adherend are not the same, were studied experimentally and numerically. Using AA2024-T3 aluminum alloy as adherend and DP460 as paste adhesive, four different types of single-lap joint samples (without spew fillet, with spew fillet at joint edges, with spew fillet at joint ends and with spew fillet at all edges) were produced for experimental studies. Stress analyses in the single-lap joint were performed with a three dimensional non-linear finite element method by considering the geometrical non-linearity and non-linear material behaviors of both adhesives (DP460) and adherend (AA2024-T3). The single lap joint with the spew fillet with different widths had a significant effect on the stress distribution. Additionally, the spew fillet increased the load carrying capacity of the joint and decreased the stress concentration of the joint.

AtıfScopus55·WoS51·OpenAlex57

İncele

Çullu, Mustafa; Arslan, Metin

This study examined the effects of antifreeze on the physical and mechanical properties of the concrete which are produced in cold weather. 30% Calcium Nitrate and 5% hydroxyethylaminemixture (HEA), Calcium Nitrate (KN) and Polyhydroxy Amine (PA) were used as additives in antifreeze. Prepared concrete samples were placed in a formwork and exposed to the frost at 0 °C, -5°C, -10°C, -15°C and -20°C for 2 days. Afterwards, concrete samples in the freezer were cured at the room temperature until the 28th day and permeable pore space volume, water absorption ratio, density, capillarity ratio, impermeability, compressive strength, static modulus of elasticity, Poisson's ratio and tensile strength values of the concrete samples were determined after the curing. In conclusion, 30% Calcium Nitrate and 5% hydroxyethylaminemixture (HEA) were found to be giving the best performance among the antifreeze types. The physical and mechanical properties of the concrete were negatively affected from all antifreeze types due to the temperature decrease of the exposed fresh concrete.

AtıfScopus47·WoS37·OpenAlex44

İncele

Çavdar, Ahmet

Polymeric fibers are cheap and popular materials used in the concrete industry, and they may improve the mechanical properties of cementitious composites under high temperature. In this study, three different types of polymeric fibers - Copolymer Polypropylene/polyethylene (CPP), Homopolymer Polypropylene (HPP), and Aramid (AR) - are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. These fibers are added into mortars in five different ratios (0.0%, 0.3%, 0.6%, 0.9% and 1.2%) by volume. The mortars are subjected to following temperatures: 21 °C (normal conditions), 100 °C (oven dry), 450 °C, 650 °C and 850 °C. It is concluded that polymeric fibers used in this study contribute to the flexural strength of mortars under normal dry conditions (100 °C). This effect continues clearly up to 450 °C and polymeric fibers show effects on flexural strength especially at 450 °C. Each fiber shows the best performance different addition ratio when flexural and compressive strength are taken into consideration at the same time under high temperature. The highest increase in flexural strength and the lowest decrease in compressive strength are at 0.3-0.9% fiber addition ratio for HPP, at 0.3-0.6% fiber addition ratio for CPP and at 0.9% fiber addition ratio for AR for every temperature.

AtıfScopus57·WoS56·OpenAlex59

İncele

Akpinar, Salih; Aydin, Murat Demir; Temiz, Şemsettin; Özel, Adnan

In the present study, it is aimed to compare mechanical behaviors of T-joint types with embedded and non-embedded supports subjected to bending moment. For this purpose, after experimental studies on the two different T-joint types were conducted, stress analyses in the T-joints were performed with a three-dimensional finite element method by considering the geometrical non-linearity and the material non-linearities of the adhesive (DP460) and adherend (AA2024-T3). Finally, stress analyses and experimental results show that the variation of the geometry of the bonding zone, e.g., embedding the supports, would change the stress distributions and strength of the joint. Additionally, it is seen that T-joints with embedded supports carry 30% more load than T-joints with non-embedded supports although their bending stiffnesses decrease.

AtıfScopus17·WoS15·OpenAlex19

İncele

Çavdar, Ahmet

The flexural strength and ductility properties of cementitious composites (mortar) under high temperature may be significantly improved by incorporating different types of fibers. In this study, four different types of fibers are added to cement mortars with the aim to investigate their mechanical contributions to mortars under high temperature, comparatively. Polypropylene (PP), carbon (CF), glass (GF) and polyvinyl alcohol (PVA) fibers are chosen for research. These fibers are added into mortars in five different ratios (0.0%, 0.5%, 1.0%, 1.50% and 2.0%) by volume. The mortars are subjected to the following temperatures: 21°C (normal conditions), 100°C (oven dry), 450°C and 650°C. The mechanical properties investigated are flexural strength, deflection and compressive strength of the cement mortars. In addition, thin sections of mortars are investigated to obtain changes in mortar because of high temperature. It is concluded that all fiber types contribute to the flexural strengths of mortars under high temperature. However, this contribution decreases with an increase in temperature. The samples with PVA show the best flexural performance (75-150%) under high temperature. CF which does not melt under high temperature also gives high flexural strength (11-85%). The compressive strengths of the mortars reduce under high temperature or with fiber addition. The highest increase in flexural strength and the lowest decrease in compressive strength is at 0.5-1.5% for CF if all temperature conditions are taken into consideration. The optimum fiber addition ratios of the samples containing PP and GF are 0.5% by volume. And for PVA, it is between 0.5% and 1.5% by volume.

AtıfScopus173·WoS152·OpenAlex178

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