The brazing joint of the Ti-6Al-4V alloy was produced with a designed brazing filler alloy and the optimized brazing temperature which is lower than the β-phase transformation of the matrix. The strength and the ductility of brazing joined Ti-6Al-4V samples were evaluated by conventional tensile tests with a DIC 2D–strain field measurement. The Widmanstätten microstructure with no voids or cracks or intermetallic compounds was found throughout the joint with a width of β-lamellar as ~ 1 μm. Due to the fine acicular α-Widmanstätten and β-lamellar, and the uniformly diffused filler elements throughout the entire joint, the strength of the joint was as much as the matrix. In addition, the hardness test results agreed well with the tensile strength tests. All fractures occurred in the matrix rather than the brazing joints. Furthermore, the maximum local tensile strain was measured as 20% in the matrix, while under the same stress, the brazing joint only reached 6.3% tensile plastic strain. Thus, the mechanical properties of the joint with the associated microstructure demonstrated that a successful brazing filler alloy has been developed for the Ti-6Al-4V alloy

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Titanium honeycomb sandwich structures are gradually used in newly developed aircrafts in China. In this study, low-velocity impact tests on the titanium honeycomb sandwich structures were carried out to obtain the impact dynamic response and investigate the typical impact damage modes and parameters including the depths and diameters of the facesheet indentation and the core crushing region. The test results showed that the maximum contact force, the diameter and depth of the indentation had strong positive correlations to the impact energy. Numerical analysis was also conducted to study the low-velocity impact behaviour of the titanium honeycomb sandwich structures by using parametric finite element models that contained all the geometric and the structural details of the titanium honeycomb cores. The numerical results successfully captured the typical low-velocity impact damage modes of the titanium sandwich structures, similar to those observed in the tests. The predicted impact dynamic response also agreed very well with the test data. By using the validated finite element models, a parameter sensitivity study on the effects of the structural parameters on the low-velocity impact damage behaviour of the titanium sandwich structures was conducted. The parametric analysis results showed that the impactor diameter, the facesheet thickness and the core cell wall thickness had positive effect on the maximum contact force, and negative effect on the indentation depth, while the height of the honeycomb core had positive effect on the contact force, but little influence on the indentation depth.

Titanium honeycomb sandwich structures are gradually used in several newly developed aircrafts in China. During the manufacturing process and aircraft service life, low-velocity impacts from foreign objects (typically stones, tools and hails, etc.), would quite likely happen and could not be completely avoided. In order to evaluate the influence of low-velocity impact damage on titanium honeycomb sandwich structures, unidirectional in-plane compression tests on both intact and impact damaged sandwich panels were conducted to obtain their failure modes and compressive failure strength. Test results showed that the low-velocity impact damage could cause the change in failure modes and a 9% to 15% decrease in the compressive failure strength. Different impact energy levels showed a limited influence on the compressive failure strength. Numerical analysis was conducted to study the compression after impact behavior of titanium sandwich panels. Parametric finite element models that contained all the geometric and the structural details of honeycomb core cells, as well as the indentation and the crushed core region, were developed in the analysis. The numerical results successfully exhibited the failure process of the intact and impact damaged titanium sandwich panels subjected to unidirectional in-plane compression, similar to what observed in the tests. The predicted compressive failure strength also agreed very well with the test data.

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