Hakan Gürün

Warm deformation and fracture behaviour of DP1000 advanced high strength steel

ABSTRACT The effect of temperature has been investigated on the mechanical properties and fracture behaviour of DP1000 advanced high-strength steel. The variation of the mechanical properties depending on temperature has been determined by performing uniaxial tensile tests at the temperatures of 25, 100, 200, 300°C at the rolling directions of 0° (rolling), 45° (diagonal), and 90° (transverse) at the strain rate of 0.0083 s−1. The yield strength and tensile strength have showed a slight decrease tendency between 25 and 200°C, but the highest value has been reached by showing an increase at 300°C temperature. The amount of elongation has not been affected significantly with the increase of the temperature. While hardening coefficient has increased due to the rising temperature, no effect has been observed on strength coefficient between 25 and 100°C, but an increase has occurred at higher temperature values.

Effect of electrical discharge machining on dental Y-TZP ceramic-resin bonding.

PURPOSE The study determined (i) the effects of electrical discharge machining (EDM) on the shear-bond strength (SBS) of the bond between luting resin and zirconia ceramic and (ii) zirconia ceramics flexural strength with the three-point bending (TPB) test. METHODS Sixty 4.8mm×4.8mm×3.2mm zirconia specimens were fabricated and divided into four groups (n=15): SBG: sandblasted+silane, TSCG: tribochemical silica coated+silane, LTG: Er:YAG laser treated+silane, EDMG: EDM+silane. The specimens were then bonded to a composite block with a dual-cure resin cement and thermal cycled (6000 times) prior to SBS testing. The SBS tests were performed in a universal testing machine. The SBS values were statistically analyzed using ANOVA and Tukeys test. To determine flexural strength, sixty zirconia specimens were prepared and assigned to the same groups (n=15) mentioned earlier. After surface treatment TPB tests were performed in a universal testing machine (ISO 6872). The flexural strength values were statistically analyzed using ANOVA and Tukeys test (α=0.05). RESULTS The bond strengths for the four test groups (mean±SD; MPa) were as follows: SBG (Control), 12.73±3.41, TSCG, 14.99±3.14, LTG, 7.93±2.07, EDMG, 17.05±2.71. The bond strength of the EDMG was significantly higher than those of the SBG and LTG (p<0.01). The average flexural strength values for the groups SBG (Control), TSCG, LTG and EDMG were 809.47, 800.47, 679.19 and 695.71MPa, respectively (p>0.05). CONCLUSIONS The EDM process improved the SBS. In addition, there was no significant adverse effect of EDM on the flexural strength of zirconia.

Influence of strain rate on tensile properties and fracture behaviour of DP600 and DP780 dual-phase steels

The influences of the strain rate on the tensile properties and fracture behaviour of DP600 and DP780 advanced high-strength sheet steels have been studied. The variation of their mechanical properties depending on the strain rate have been researched by applying uniaxial tensile tests at three different strain rates (0.001, 0.01, 0.06 s−1). The influences of strain rate on fracture behaviour have been investigated by displaying the fracture surfaces of the material. Strain rate increase has been determined to increase the yield strength, tensile strength, total elongation and hardening rate. The strain hardening coefficient has been found not to be significantly affected by the strain rate. It has been determined that, the fracture has occurred faster during necking while load-carrying capacity has increased with strain rate increase.

CuZn30 sac malzemenin kesme işlemlerinde kesme boşluğu etkilerinin sinir ağı ile modellenmesi - karşılaştırmalı bir çalışma

Clearance effects on the product quality and blanking force in sheet metal blanking process are initially investigated experimentally, and then modelled through neural network (NN) approach. Using eleven different clearances from 8% to 18% with a sampling rate of 1%, blanking processes are applied to sheet material CuZn30 with a thickness of 1mm using a modular template. During the experiments, blanking force, smooth sheared/fractured rate and burr height for the resulting products are measured for each of clearance value and a certain portion of them are taken as example patterns to train the developed feedforward NN. Several NN-based estimation results are presented which verify that a satisfactory neural network model is attained for the concerned parameter estimations. Moreover, comparisons with a recent study that benefits from fuzzy logic as an estimator tool are also presented for the same system. We realize that estimating performance is improved using the NN and a significant contribution of our proposal is that its design is much simpler than that of its counterpart which requires proper and sufficient expert knowledge for tuning of characteristic parameters such as numbers and shapes of membership functions, linguistic control rules.

Statistical Evaluation of the Influence of Temperature and Surface Roughness on Aluminium Sheet Metal Forming

The influences of temperature and surface roughness on the forming of the AA3003H111 aluminium alloy sheet material have been investigated by using the finite element method. For this purpose, material cards have been firstly created based on the sheet material behaviour at different deformation temperatures. As a result of the forming analyses performed at different temperature values and surface roughness values, it has been determined that the increase in the surface roughness reduces the amount of thinning while it increases the amount of forming force and the springback. It has also been determined that there is a slight increase in the amount of thinning, while the temperature rise reduces the amount of forming force and the springback. In addition, the influence levels of temperature and surface roughness have been determined by statistical analyses.

The Relationship of Burr Height and Blanking Force with Clearance in the Blanking Process of AA5754 Aluminium Alloy

The effect of clearance and sheet thickness in the AA5754 sheet material blanking process on the burr formation and blanking force was examined experimentally. Measurements of the burr height and blanking force were performed in a modular die with six different clearance values (8 %, 10 %, 12 %, 14 %, 16 % and 18 %) by applying the blanking process to the AA5754 sheet metal of 1 mm and 2 mm in thickness. The influence rate of parameters affecting the burr height, the blanking force, and the mathematical relationship between them were identified by using the analysis of variance (ANOVA) and the regression analysis. Thus, it was determined that the burr formation increased with increased clearance and that the blanking force was not affected in the same proportion. In addition, it was found that the sheet thickness and clearance affected the burr formation at rates of 23.24 % and 76.15 %, respectively; on the other hand, the sheet thickness and clearance affected the blanking force at rates of 99.72 % and 0.24 %, respectively.

Microstructure based modelling of stress–strain relationship on dual phase steels

ABSTRACT The deformation in microstructures of DP600, DP800 and DP1000 commercial advanced high strength steels have been researched through using the representative volume element method. For this purpose, deformation analyses have been carried out by transferring geometrical models and mechanical properties of phases of each material to the finite element software. Deformation relation between ferrite and martensite phases was determined. According to the loading direction, Shear bands have been observed to occur in the range of approximately 40°–45°. It has been understood that the failure mode is shear for DP600, DP800 and DP1000 steels. Crack propagation has been observed to occur in the ferrite phase trapped at the martensite grain boundary.

Experimental Examination of Effects of Punch Angle and Clearance on Shearing Force and Estimation of Shearing Force Using Fuzzy Logic

A significant challenge faced when using blanking/piercing to machine sheet metal is the handling of the shearing force required for high strength and thick stock. Increased shearing forces lead to the requirement of higher performance expected from the pressing machine and result in increased wear on the punch tool and die. Clearance, employed to increase precision and quality in blanking/piercing operations, affects the shearing force as well. One of the techniques used to reduce the force required is the employment of a punch shear angle. In this study, the effects of punch shear angle and clearance on the forces required for blanking/piercing were examined on a grade of steel broadly used in the manufacturing industry, DC01. Experiments were carried out using five different punch shear angles, namely 0°, 2°, 4°, 8°, and 16°. Six matrices with varying clearance rates (0.4%t, 0.5%t, 0.6%t, 0.7%t, 0.8%t, and 0.9%t) were used in this study, and these clearances were altered by modular matrices on the die. This study shows that shearing forces can be reduced by 80 % when 16° punch angle is used. The results of the experiments were transferred to a fuzzy logic model to obtain extrapolated results for intermediate values which had not been obtained from the experiments. The results obtained from the experiments and the output from the fuzzy logic model were compared and found to be highly similar. These results have showed that the model developed using fuzzy logic can be used to determine different shear angles and clearance values.