Uncoupled material model of ductile fracture with directional plasticity

Proposed paper deals with the application of plastic response with directional distortional hardening (DDH) in uncoupled ductile fracture model and comparison of the results with the same ductile fracture model based on isotropic J2 plasticity. The results of simulations have proven not negligible role of model of plasticity and the response of the model with DDH plasticity is closer to reality then the one of the model with isotropic plasticity

Fracture Toughness Determination with the Use of Miniaturized Specimens

Fracture mechanics has been used for decades nowadays, and methods have been well established in the community especially for standard-sized specimens. As it was mainly developed for large structure assessment against the brittle failure, standardized specimens are of large size at present. However, in many cases, these standard specimens are not possible to apply due to size requirements of the available experimental material or the size of the component considered. These can be cases of residual service life assessment of in-service components, local properties determination (e.g., across weld), anisotropy determination and assessment of mechanical properties of newly developed materials under laboratory conditions (e.g., SPD processed materials, etc.). Therefore, development of new methods using significantly smaller specimens has to be carried out, and procedures using smaller-sized specimens together with their validity limits and relation to standardly obtained results have to be provided in order to provide solution for wide applications

New approach for determination of strain rate sensitivity of mild steel dc01 under stack compression and uniaxial tensile test

Deformation under uniaxial tensile loading with using Digital Image Correlations (DIC) is the easiest way to analyze the material behavior in sheet metal forming. In order to determine the plastic parameters such as hardening, anisotropy and strain rate sensitivity at higher strain level, equi-biaxial stress state is prerequisite. As reported in the literature, Bulge tests are frequently used for this purpose, but in this work, stack compression test is used as an alternative. In this experiment, deformation in the middle layer where the friction effect is the lowest was monitored using two pairs of DIC systems in rolling and transversal directions. Uniaxial tensile tests as well as stack compression tests were performed on mild ferritic steel DC01 at different strain rates, from 0.001 −1 to 10 −1. Strain rate sensitivity parameter was investigated at different level of strains for both experiments and strain rate sensitivity profiles were obtained. Results show a decrease of material strain rate sensitivity with increasing the true strain

Crack lengths calculation by unloading compliance technique for Charpy size specimens

The problems with the crack length determination by the unloading compliance method are well known for Charpy size specimens. The final crack lengths calculated for bent specimens do not fulfil ASTM 1820 accuracy requirements. Therefore some investigations have been performed to resolve this problem. In those studies it was considered that measured compliance should be corrected for various factors, but satisfying results were not attained. In the presented work the problem was attacked from the other side, the measured specimen compliance was taken as a correct value and what had to be adjusted was the calculation procedure. On the basis of experimentally obtained compliances of bent specimens and optically measured crack lengths the investigation was carried out. Finally, a calculation procedure enabling accurate crack length calculation up to 5mm of plastic deflection was developed. Applying the new procedure, out of investigated 238 measured crack lengths, more than 80% of the values fulfilled the ASTM 1820 accuracy requirements, while presently used procedure provided only about 30% of valid results. The newly proposed procedure can be also prospectively used in modified form for the specimens of different than Charpy size

Crack initiation determination for Charpy size specimens

An investigation in the field of the crack initiation determination for Charpy size specimens was carried out. An extensive literature survey of published methods for the crack initiation was performed. Methods based on the stretch zone width measurement, blunting line, multiple gauge measurement, electric potential drop, compliance changing rate, acoustic emission, ultrasonic method and magnetic emission are discussed in the theoretical part of the report. Analytical methods for the critical J-integral evaluation were also taken into account, as well as the expressions for the J-integral calculation. On the basis of the theoretical survey suitable measurement methods were chosen and applied in the experimental programme to several different materials. Namely blunting line related methods, multiple gauge methods, electric potential drop and compliance changing rate methods were used. The initiation J-integrals were evaluated with use of wide range of evaluation procedures and compared together in order to find a reliable method for the crack initiation determination. There was not found a universal method for the crack initiation determination. The performance of the methods was varying in dependence on the investigated material, so the results enable to choose perspective method for considered case

Crack initiation determination for Charpy size specimens

An investigation in the field of the crack initiation determination for Charpy size specimens was carried out. An extensive literature survey of published methods for the crack initiation was performed. Methods based on the stretch zone width measurement, blunting line, multiple gauge measurement, electric potential drop, compliance changing rate, acoustic emission, ultrasonic method and magnetic emission are discussed in the theoretical part of the report. Analytical methods for the critical J-integral evaluation were also taken into account, as well as the expressions for the J-integral calculation. On the basis of the theoretical survey suitable measurement methods were chosen and applied in the experimental programme to several different materials. Namely blunting line related methods, multiple gauge methods, electric potential drop and compliance changing rate methods were used. The initiation J-integrals were evaluated with use of wide range of evaluation procedures and compared together in order to find a reliable method for the crack initiation determination. There was not found a universal method for the crack initiation determination. The performance of the methods was varying in dependence on the investigated material, so the results enable to choose perspective method for considered case

Strengthening from Cu Addition in 0.2C-(1-2)Mn Steels during Tempering

The strengthening effects of Cu and Mn were studied in steels, which contained 0.2% C and were micro-alloyed with B and Ti. The experimental steels were austenitized and quenched in order to take Mn and Cu into solid solution. The subsequent tempering of martensitic structures resulted in higher strengths in the materials alloyed with Cu than in the steel without Cu addition. Tensile testing and metallographic analyses were performed. The kinetics and magnitude of precipitation strengthening were measured for different tempering temperatures and times. Presumed synergistic effects between Cu precipitation strengthening and higher levels of Mn were observed

New approach for determination of strain rate sensitivity of mild steel dc01 under stack compression and uniaxial tensile test

Deformation under uniaxial tensile loading with using Digital Image Correlations (DIC) is the easiest way to analyze the material behavior in sheet metal forming. In order to determine the plastic parameters such as hardening, anisotropy and strain rate sensitivity at higher strain level, equi-biaxial stress state is prerequisite. As reported in the literature, Bulge tests are frequently used for this purpose, but in this work, stack compression test is used as an alternative. In this experiment, deformation in the middle layer where the friction effect is the lowest was monitored using two pairs of DIC systems in rolling and transversal directions. Uniaxial tensile tests as well as stack compression tests were performed on mild ferritic steel DC01 at different strain rates, from 0.001 \u1d460\u1d460−1 to 10 \u1d460\u1d460−1. Strain rate sensitivity parameter was investigated at different level of strains for both experiments and strain rate sensitivity profiles were obtained. Results show a decrease of material strain rate sensitivity with increasing the true strain