Search Results (3)

The deformation mechanism of the Ti-6Al-4V (wt.%) alloy with globular structure was studied under conditions of quasi-static and high-strain compression with rates 10⁻³ s⁻¹ and 2.1–3.3 × 10³ s⁻¹, respectively. High-strain compression was conducted using a Split Hopkinson Pressure Bar (SHPB). The details of the deformation mechanism were evaluated based on the analysis of the deformation hardening curves using the strain hardening exponent concept developed for titanium alloys in tension conditions. The used approach allowed us to identify the stages of plastic deformation observed and the controlling phase in deformation of two-phase alloy through the assessment of the strengthening index, n. It has been found that three deformation stages can be identified in quasi-static conditions. However, when the alloy is compressed at a high strain rate, the third deformation stage does not develop due to the high process rate. Further analysis of deformation curves reveals the leading role of the β-phase under the quasi-static conditions and the essential contribution of the second, α-phase, at a high compression rate. The findings on the deformation mechanism based on the analysis of hardening curves were supported by a detailed structural study. Full article

We develop a new flow model based on the Swift method, which is both versatile and accurate when used to describe flow stress in terms of strain hardening and damage softening. A practical issue associated with flow stress at room temperature is discussed in terms of tensile testing of a cylindrical specimen; we deal with both material identification and finite element predictions. The flow model has four major components, namely the stress before, at, and after the necking point and around fracture point. The Swift model has the drawback that not all major points of stress can be covered simultaneously. A term of strain to the third or fourth power (the “second strain hardening exponent”), multiplied and thus controlled by a second strain hardening parameter, can be neglected at small strains. Any effect of the second strain hardening exponent on the identification of the necking point is thus negligible. We use this term to enhance the flexibility and accuracy of our new flow model, which naturally couples flow stress with damage using the same hardening constant as a function of damage. The hardening constant becomes negative when damage exceeds a critical value that causes a drastic drop in flow stress. Full article

Conventional sensor structure design and related fracture mechanics analysis are based on the single J-integral parameter approach of elastic-plastic fracture mechanics (EPFM). Under low crack constraint cases, the EPFM one-parameter approach generally gives a stress overestimate, which results in a great cost waste of labor and sensor components. The J-A two-parameter approach overcomes this limitation. To enable the extensive application of the J-A approach on theoretical research and sensor engineering problem, under small scale yielding (SSY) conditions, the authors developed an estimate method to conveniently and quickly obtain the constraint (second) parameter A values directly from T-stress. Practical engineering application of sensor structure analysis and design focuses on three-dimensional (3D) structures with biaxial external loading, while the estimate method was developed based on two-dimensional (2D) plain strain condition with uniaxial loading. In the current work, the estimate method was successfully extended to a 3D structure with biaxial loading cases, which is appropriate for practical sensor design. The estimate method extension and validation process was implemented through a thin 3D single edge cracked plate (SECP) specimen. The process implementation was completed in two specified planes of 3D SECP along model thickness. A wide range of material and geometrical properties were applied for the extension and validation process, with material hardening exponent value 3, 5 and 10, and crack length ratio 0.1, 0.3 and 0.7. Full article