Bending Limit Curves in Sheet Metal Bending Evaluation

Bending and hemming process are used in automotive industries for assembling the car body panel.The main failure mechanism under bending loads is the intercrystalline fracture. This is due to the fact that the Forming Limit Curve (FLC) describes first occurrence of membrane instability and no material failure in consequence of an intercrystalline fracture at bending.The FLC fails to predict the formability in hemming processes since difference in failure mechanism. A new failure criterion, the so-called Bending Limit Curve (BLC) has been developed. In this work, the left hand side BLCs are experimentally determined for Advanced High Strength Steel grade DP1000, Stainless Steel grade SUS430 and Deep Drawing Steel grade SPCC having a thickness of 1.0 mm. The influence of various bending radii and level of pre-strain on the bending strains are investigated and discussed by using the Three Point Bending Test. Bendability of investigated materials are evaluated by using optical strain measurement system GOM-Aramis to determine maximal achievable bending strain on the specimens. The developed left hand side BLCs were found to be higher level than conventional FLCs. The bigger bending radius established lower bending limit strain. The higher bending strain was obtained from the higher pre strain level.

Structure and Properties of the Aluminide Coatings on the Inconel 625 Superalloy

The research samples used in this study were based on the Inconel 625 alloy; the examined samples were coated with aluminide films deposited in a low-activity chemical vapor deposition (CVD) process. The samples’ microstructure was investigated with optical and electron microscopy and energy dispersive X-ray spectroscopy analysis. Hardness measurements were performed using Vickers and Berkovich test methods. The adhesion of the aluminide coating was determined by fractography. It was shown that the fracture mechanism was different for the respective zones of the aluminide coating and the substrate material. The outer zone of the aluminide coating is characterized by an intercrystalline fracture, with a small contribution of transcrystalline fracture within individual grains (large crystallites in the bottom of the zone, composed of smaller crystallites, also show an intercrystalline fracture). The substrate material exhibited a ductile intercrystalline fracture. Based on this investigation, an increase of the microhardness of the material occurring at loads below 0.2 N was observed. When determining microhardness of aluminide coating it is necessary to take into account the optimal choice of the indentation tip.

Microstructures, Properties and Fracture Behavior of Solidified TiC-TiB2 Composites with Increasing Content of TiB2

By adjusting the mole ratio of C and B elements in combustion system, solidified TiC-TiB2 composites with different TiB2 mole fraction were achieved by combustion synthesis in high-gravity field. XRD, FESEM and EDS results showed that with increasing TiB2 content, the matrix of TiC-TiB2 composite ceramics transformed a number of fine TiB2 platelets from the TiC spherical grains, and fine-grained even ultrafine-grained microstructures were achieved in solidified TiC-50mol% TiB2 due to eutectic growth under rapid solidification of the ceramic. Properties showed that relative density, Vickers hardness and flexural strength of TiC-50mol%TiB2 simultaneously reached the maximum values of 21.5 ± 1.5 GPa and 860 ± 35 MPa , whereas TiC-66.7mol%TiB2 presented the maximum fracture toughness of 13.5 ± 1.5 MPa • m0.5. FESEM fractography analyses of the ceramics exhibited a mixed mode of transcrystalline fracture of TiC spherical grains and intercrystalline fracture of TiB2 platelets, and the tendency of intercrystalline fracture was obviously enhanced with increasing TiB2 content to be 66.7 mol%, resulting in enhanced toughening mechanisms of crack deflection, crack-bridging and pull-out by fine TiB2 platelets, thus, the highest flexural strength was achieved in TiC-50mol%TiB2 due to the achievements of both fine-grained microstructures and high fracture toughness in the full-density solidified ceramics.