Formability of dual phase steels in electrohydraulic forming

Experimental investigation and numerical simulation of the influence of the strain rate in laser forming are presented. To isolate and effectively study the strain rate effects, which are temperature dependent, a constant peak temperature method is developed with the aid of numerical modeling and solution. Under the condition of the constant peak temperature, the effects of strain rate on forming efficiency, residual stress and hardness of the formed parts are studied both experimentally and numerically. In the numerical model, the temperature dependence and strain-rate dependence of the flow stress and other material properties are considered. The simulation results are consistent with the experimental observations.

Numerical and Experimental Study of Strain Rate Effects in Laser Forming

Numerical modelling of electrohydraulic free-forming and die-forming of DP590 steel

Assessment of the mechanical properties of structural steels characterizing their strength and deformation parameters is an essential problem in the monitoring of structures that have been in operation for quite a long time. The properties of steel can change under the influence of loads, deformations, or temperatures. There is a problem of express determination of the steel grade used in structures—often met in the practice of civil engineering or machinery manufacturing. The article proposes the use of artificial neural networks for the classification and clustering of steel according to strength characteristics. The experimental studies of the mechanical characteristics of various steel grades were carried out, and a special device was developed for conducting tests by shock indentation of a conical indenter. A technique based on a neural network was built. The developed algorithm allows with average accuracy—over 95%—to attribute the results to the corresponding steel grade.

https://www.mdpi.com/1996-1944/13/11/2445/pdf

Artificial Neural Networks in Classification of Steel Grades Based on Non-Destructive Tests.

This study examines the effectiveness of using curvilinear steel fibers to enhance the pullout resistance of conventional straight steel (S-) fiber for an ultra-high-performance concrete (UHPC) matrix. Because structures composed of UHPC are subjected to various loading conditions and have random fiber orientations, three different loading rates ranging from static (0.018 mm/s) to impact (up to 906.2 mm/s) and two inclination angles of 0° and 45° were adopted. To fabricate the novel curvilinear steel fibers, five different curvatures were also utilized. Test results indicated that the curvilinear fibers provided a clearly higher pullout resistance than that of the conventional S-fiber, and the effectiveness increased with the curvature, regardless of the inclination angle and loading rate. Higher bond strengths were obtained for the S- and curvilinear fibers when they were inclined at 45° rather than aligned. In general, the bond strengths and pullout energies of the S- and curvilinear fibers in UHPC were improved by increasing the loading rate, and a higher loading rate sensitivity on the bond strengths was observed in aligned fibers than in inclined fibers. The matrix spalling phenomenon was only observed in an inclined state and became more significant with an increasing curvature and loading rate. The developed curvilinear fibers provided noticeably smaller matrix spalling areas than the conventional deformed steel fibers under both static and impact conditions, owing to the mitigated stress concentration. Thus, these may be worthy of attention as a novel reinforcing fiber type for UHPC composites.

Benefits of curvilinear straight steel fibers on the rate-dependent pullout resistance of ultra-high-performance concrete

1.

Within the limits of experimental error, the impact compressibility of different aluminum alloys in the test pressure range is weakly dependent on chemical composition, treatment process, and material strength.




2.

Resistance to deformation in the high strain rate region increases with increasing strain rate, and the boundary for a marked effect of strain rate on its resistance moves into the region of higher rates.




3.

In the case of the absence of a correlation between strength properties with uniaxial stress and uniaxial strain states, their sensitivity to loading rate may be connected with a single viscosity factor.

Mechanical properties of a high-strength aluminum alloy with shock loading

The results are presented of mechanical tensile and shear tests of steels of different strength levels with plastic strain rates of 3·10−3–105 sec−1. The changes in the characteristics of strength, plasticity, and microstructure are analyzed in relation to the strength level of the steel and loading rate. For steels of different structural classes at high deformation rates (approximately up to 105 sec−1) a significant increase in the characteristics of strength and plasticity is observed.

Influence of loading rate on the mechanical properties of steels of different strength levels

Dynamic shear resistance of structural materials

Dynamic strength and crack resistance of metals at low temperatures

Results are given for mechanical tests on a number of low-carbon steels in uniaxial tension and compression in the strain rate range 10−3–4·103 sec−1 and at temperatures of 293–573 K. An increase is confirmed for strength and ductility characteristics with an increase in strain rate. It is shown that the sensitivity of metals to strain rate depends on the specific temperature and rate conditions of loading. On the basis of experimental data obtained analytical dependences are suggested for the resistance of materials to deformation on the degree and rate of deformation, and also on temperature.

A. P. Vashchenko

Papers

Mechanical properties of a high-strength aluminum alloy with shock loading

Influence of loading rate on the mechanical properties of steels of different strength levels

Dynamic shear resistance of structural materials

Dynamic strength and crack resistance of metals at low temperatures

Mechanical properties of low-carbon steels over a wide range of temperatures and strain rates applied to processes of thin sheet rolling