Strain Amplitude Dependence of High Damping Grp/Mg97Zn1Y2 Composites Ranging from Anelastic to Microplastic

In this paper, the damping capacities and damping mechanisms of high damping, graphite-reinforced Mg97Zn1Y2 composites were investigated. Composites consisting of different graphite particle sizes (24, 11, and 3 μm) were designed and prepared using the casting method. The microstructure of the composites was examined using optical microscopy (OM) and transmission electron microscopy (TEM), which confirmed that the graphite particles were successfully planted into the Mg97Zn1Y2 matrix. Measurements made with a dynamic mechanical analyzer (DMA) showed that the Grp/Mg97Zn1Y2 composite has a high damping capacity. At the anelastic strain amplitude stage, the damping properties of the Grp/Mg97Zn1Y2 composites were found to be higher than those of the Mg97Zn1Y2 alloy. Furthermore, decreasing the graphite particle size was found to improve the damping properties of the Grp/Mg97Zn1Y2 composites. At the microplastic strain amplitude stage, the damping properties of the Mg97Zn1Y2 alloy were found to be higher than those of the Grp/Mg97Zn1Y2 composites. Moreover, the damping properties of the Grp/Mg97Zn1Y2 composites were found to decrease with increasing graphite particle size. The reason for the increased damping of the Grp/Mg97Zn1Y2 composites during the anelastic strain amplitude stage can be attributed to the increase in the number of damping sources and weak interactions among the dislocation damping mechanisms. At the microplastic strain amplitude stage, the damping properties of the composite are mainly affected by the activation volume of the slipped dislocation.

Assessment of Springback Behaviour of 800-1200 MPa Dual-Phase Steel Grades

Springback occurs in sheet metal forming due to elastic strain recovery after removal of process forces respectively after opening of the tool. For this reason, a precise description of springback requires the elastic stress-strain relationship described by the Young’s modulus as well as the internal stress distribution of the part before unloading. In this context, the Bauschinger effect influences the stress state before springback due to premature plastification during load reversal or load path change. As is well known, the stress-strain curve of a material during unloading is non-linear because of additional microplastic strain, which is reflected in a decrease of the Young’s modulus. The aim of this work is to characterize the aforementioned phenomena and their effect on springback for three dual-phase steels namely DH800, DH1000 and DP1200LY. For this purpose, cyclic tensile-compression tests as well as loading and unloading loops within uniaxial tensile tests are performed at different plastic strains. To evaluate the springback behavior of the investigated materials, two different hat-profiles geometries are investigated. By comparing the springback of dual-phase steels on part level, the significance of different material influences with regard to springback is evaluated. The results show that the investigated dual-phase steels exhibit a pronounced Bauschinger effect and a considerable amount of microplastic strain with increasing total strain. However, the comparison between the springback of the hat-profiles and the determined material parameters proves a significant influence of the elastic strain on springback, while microplastic strain and the Bauschinger effect have a minor influence.

The Finite Element Mesomechanics Simulation of Polycrystal Martensitic Transformation’s Plastic Strain

The plastic strain finite element mesomechanics simulation of polycrystal martensitic transformation bring up non-linear model of influence microscopic phase transition rate and stress. Further developement and application of Marc and on the base of microscopic chemical energy distribution, evenly. As the simulation showed: 1) Early into the plasticity than that of single crystal.2) Microplastic strain distribution is not uniform, microplastic strain maximum, minimum value ratio in different incremental step fluctuate greatly. 3) Meso martensitic transformation is not uniformly distributed, and uneven degree decreases with increment step. 4) The macro transformation rate simulation curves are exponential trend, and into the fully plastic state reached the point.

Strain Amplitude Dependence of Damping Capacity in High Damping Mg-Based Alloys Continuously Extending to Microplastic Strain

An investigation on low frequency strain amplitude dependence damping characteristic of as-cast high damping Mg-based alloys continuously extending to microplastic strain was carried out. Two-stage damping behavior via strain amplitude was particularly reported. The first is the strain amplitude strongly dependent part due to breakaway loss and the second is the strain amplitude weakly dependent part due to microplastic deformation loss, which is also frequency dependent. The damping mechanism is discussed in detail.

Elastic and Inelastic Recovery After Plastic Deformation of DQSK Steel Sheet

Strain recovery after plastic prestrain and associated elastic and inelastic behavior during loading and unloading of DQSK steel sheet are measured. Average tangent modulus and Poisson’s ratio during unloading and reloading are found to differ from their elastic values in the undeformed state, and they also vary as a function of stress. This modulus, often referred to as the “springback modulus,” decreases with plastic prestrain rapidly for prestrain values <2 percent and decays slowly for larger values of prestrain, while the average Poisson’s ratio during unloading increases with plastic prestrain initially rapidly and then remains almost unchanged at larger prestrain. Changes in the springback modulus and Poisson’s ratio are shown to be due to recovery of microplastic strain and not due to viscoelastic effects. Springback modulus and Poisson’s ratio are anisotropic, showing a maximum in modulus and a minimum in Poisson’s ratio at 45 deg to rolling direction. To describe the combination of recoverable inelastic and elastic deformation as a function of plastic prestrain, a set of equations has been developed based upon a previously developed constitutive model. Calculated results are capable of explaining experimental results on modulus and Poisson’s ratio changes. Implication of the results on “springback” is illustrated and empirical relations are obtained.