Calibration of the Johnson-Cook Material Model for Additively Manufactured 304L SS Parts: Modeling and Experiments

Selective laser melting (SLM) is a type of additive manufacturing technique which uses a powder bed to form complex metal parts in a layer-by-layer process. This study aims to understand the material flow of parts manufactured by SLM process using 304L stainless steel powder, which is widely used in numerous applications. The tensile specimens were manufactured using 304LSS powder through SLM process. Low strain-rates, high temperature tensile tests were carried out to calibrate the parameters of the constitutive Johnson-Cook strength model. To conduct the tensile tests, different temperatures (25 oC, 150 oC and 250 oC) and strain-rates (0.1 s-1, 0.01 s-1 and 0.001 s-1) were used. The material model developed was used in numerical simulation of the tensile tests and compared with the experimental results.Mechanical Engineerin

JOHNSON-COOK FAILURE MODEL FOR ADDITIVELY MANUFACTURED 304L STAINLESS STEEL PARTS

Laser powder bed fusion (LPBF) process is a type of additive manufacturing technique which uses a powder bed to form complex metal parts in a layer-by-layer process. This study aims to understand the damage initiation in the parts manufactured by LPBF process using 304L stainless steel powder, which is widely used in numerous applications. The tensile specimens were manufactured using 304LSS powder through LPBF. Tensile specimens with varying notches were tested to calibrate the parameters of the constitutive Johnson-Cook failure model. To obtain the strength parameters, the tensile tests were performed at different temperatures and strain-rates. The material model developed was used in numerical simulation of the tensile tests and compared with the experimental results.Mechanical Engineerin

Material model for modeling clay at high strain rates

This paper was accepted for publication in the journal International Journal of Impact Engineering and the definitive published version is available at http://dx.doi.org/10.1016/j.ijimpeng.2015.11.005Modeling clay is a soft malleable material made from oils and waxes. This material is fundamental for ballistic evaluation of body armors because it is used as backing material in ballistic tests. After a ballistic impact, a back-face indentation is measured to assess performance of the armor. Due to the important role of modeling clay in this particular application, its mechanical characterization and comprehension of penetration mechanics are essential for development of new personal protection systems. This paper presents a two-step computational methodology to calibrate parameters of a Cowper-Symonds material model for modeling clay at characteristic strain rates up to 1.8×104 s-1. In the first stage, a high-speed camera is used to record the penetration of a gas-gun launched cylindrical mass with a hemispherical cap into a block of clay. Image-processing software is used to capture the tail of the projectile as it penetrates into the clay. These data are then used to sample the penetration depth as function of time. In the second stage, an in-house developed model of penetration, based on both the spherical cavity expansion theory and the Tate penetration equation, is used to determine, by inverse analysis, the parameters of the Cowper-Symonds clay model. The proposed constitutive relationship for clay and the determined material parameters can be applied accurately to problems involving high strain rates

Engineering model for low-velocity impacts of multi-material cylinder on a rigid boundary

Modern ballistic problems involve the impact of multi-material projectiles. In order to model the impact phenomenon, different levels of analysis can be developed: empirical, engineering and simulation models. Engineering models are important because they allow the understanding of the physical phenomenon of the impact materials. However, some simplifications can be assumed to reduce the number of variables. For example, some engineering models have been developed to approximate the behavior of single cylinders when impacts a rigid surface. However, the cylinder deformation depends of its instantaneous velocity. At this work, an analytical model is proposed for modeling the behavior of a unique cylinder composed of two different metals cylinders over a rigid surface. Material models are assumed as rigid-perfectly plastic. Differential equation systems are solved using a numerical Runge-Kutta method. Results are compared with computational simulations using AUTODYN 2D hydrocode. It was found a good agreement between engineering model and simulation results. Model is limited by the impact velocity which is transition at the interface point given by the hydro dynamical pressure proposed by Tate

Material model for modeling clay at high strain rates

Modeling clay is a soft malleable material made from oils and waxes. This material is fundamental for ballistic evaluation of body armors because it is used as backing material in ballistic tests. After a ballistic impact, a back-face indentation is measured to assess performance of the armor. Due to the important role of modeling clay in this particular application, its mechanical characterization and comprehension of penetration mechanics are essential for development of new personal protection systems. This paper presents a two-step computational methodology to calibrate parameters of a Cowper-Symonds material model for modeling clay at characteristic strain rates up to 1.8×104 s-1. In the first stage, a high-speed camera is used to record the penetration of a gas-gun launched cylindrical mass with a hemispherical cap into a block of clay. Image-processing software is used to capture the tail of the projectile as it penetrates into the clay. These data are then used to sample the penetration depth as function of time. In the second stage, an in-house developed model of penetration, based on both the spherical cavity expansion theory and the Tate penetration equation, is used to determine, by inverse analysis, the parameters of the Cowper-Symonds clay model. The proposed constitutive relationship for clay and the determined material parameters can be applied accurately to problems involving high strain rates

The Influence of Build Parameters on the Compressive Properties of Selective Laser Melted 304L Stainless Steel

Process parameters used during Selective Laser Melting (SLM) process have significant effects on the mechanical properties of the manufactured parts. In this study, the influence of two build parameters (build orientation and hatch angle) on the compressive properties of 304L stainless steel was evaluated. SLM 304L samples were manufactured using three hatch angles, 0°, 67°,105° and two orientations, z-direction and x-direction, and tested using a compression frame according to ASTM E9-09. Bulk density was measured according to ASTM C373-17 before compression. Properties evaluated were the bulk density, yield strength, strength at 15% plastic-strain and strength at 30% plastic-strain. Results showed that bulk density varied minutely with respect to variation in hatch angle and build orientation, but compressive yield strength and plastic flow stress were strongly influenced by these two process parameters. Highest compressive yield strength was measured when samples were built in the x-direction using hatch angle 67°.Mechanical Engineerin

Effect of SMAW manufacturing process in high-cycle fatigue of AISI 304 base metal using AISI 308L filler metal

El proceso de soldadura por arco de metal protegido (SMAW) se usa comúnmente en muchas aplicaciones debido a su alta versatilidad en la fabricación de piezas, componentes y ensamblajes industriales. Este artículo trata sobre el efecto del proceso SMAW en la fatiga de ciclo alto del acero inoxidable austenítico AISI 304 utilizando metal de aportación AISI 308L. Se evaluaron dos parámetros (factores) diferentes del proceso de fabricación: el tipo de recubrimiento del electrodo y el aporte de calor en el proceso de soldadura. Se compararon tres revestimientos de electrodos diferentes: E308L-15, E308L-16 y E318L-16 Premium. Además, se utilizaron tres niveles de entrada de calor diferentes en el proceso de soldadura para cada recubrimiento de electrodo ("bajo", "medio" y "alto"). Para esta aplicación de soldadura, se utilizaron placas laminadas en frío de 300 mm de longitud, 76,2 mm de ancho, 6,4 mm de espesor de AISI / SAE 304 como material base. formando juntas tipo V-groove en ellos. Después de la soldadura, caracterización de la microestructura mediante microscopía óptica y electrónica de barrido; composición de análisis químico; Ensayo de dureza HRB; Se evaluó la prueba de tracción y el índice de ferrita (FN) de las uniones soldadas. Las pruebas de fatiga se realizaron en la máquina INSTRON 8872. Para analizar los resultados de fatiga, se utilizó el Análisis Cuantitativo de Ensayos de Vida Acelerada, donde se trazaron gráficas S max -N entre todos los factores experimentales (como un experimento factorial). Se encontró que la solidificación de la soldadura muestra un crecimiento dendrítico con morfologías tanto ventriculares como lathy. Los depósitos de electrodos E308L-15 tienen mejor resistencia a la fatiga axial de ciclo alto que los otros depósitos de electrodos. Además, Encontramos que la resistencia a la fatiga de ciclo alto de los depósitos se mejora con menores aportes de calor del proceso de soldadura y mayor FN. Las fallas de material se localizaron entre el depósito de soldadura, a través de la orientación dendrítica en la microestructura que también condujo al crecimiento de la fisura.The shielded metal arc welding (SMAW) process is commonly used in many applications due to its high versatility in the manufacturing of industrial parts, components and assemblies. This paper is about the effect SMAW process on the high-cycle fatigue of austenitic stainless steel AISI 304 using AISI 308L filler metal. Two different parameters (factors) of the manufacturing process were evaluated: type of electrode coating and heat input in the welding process. Three different electrode coating were compared: E308L-15, E308L-16 and E318L-16 Premium. Additionally, three different heat inputs levels were used in the welding process for each electrode covering (“low”, “medium” and “high”). For this welding application, cold rolled plates 300 mm length, 76.2 mm wide, 6.4 mm thick of AISI/SAE 304 were used as base material, making up V-groove type joints on them. After welding, microstructure characterization using optical and scanning electron microscopy; chemical analysis composition; HRB hardness test; tensile test and ferrite number (FN) of the welded joints were evaluated. Fatigue tests were conducted in the INSTRON 8872 machine. To analyze the fatigue results, Quantitative Analysis Accelerated Life Testing was used, wherewith Smax-N graphs were plotted among all the experimental factors (as a factorial experiment). It was found that solidification of weld shows dendrite growth with both ventricular and lathy morphologies. The E308L-15 electrode deposits have better resistance to high cycle axial fatigue than the other electrode deposits. Furthermore, we found that the high-cycle fatigue resistance of the deposits is enhanced at lower heat inputs of welding process and greater FN. Material failures were localized among the weld deposit, through the dendrite orientation on microstructure that also led the growth of the crac

Effect of Thermal History on the Deformation of Non-metallic Inclusions During Plain Strain Compression

The deformation of inclusions in the steel was affected by the thermal history during the physical simulation of steel processing. After plain strain compression with a reduction of 30%, the average aspect ratio of inclusions in the steel sample cooled down to 1673 K from semi-solid state was 1.89, which was significantly higher than 1.29 in the steel sample heated persistently up to the same temperature. The mechanism was revealed by inclusion transformation