Muhammad Jawad Qarni

Numerical Investigation of Residual Stresses and Distortions due to Multi-Pass Welding in a Pipe-Flange Joint

This paper presents a numerical simulation for examining temperature fields, residual stresses, and distortions in multi-pass welding of a pipe-flange joint. A sequentially coupled transient non-linear thermo-mechanical three-dimensional finite-element model is developed to simulate four-pass tungsten inert gas welding process. An ANSI class 300{#} flange is welded with a 6 mm thick, 200 mm long, and 100 mm nominal diameter pipe, using a single V-groove butt joint with a 1.2 mm root opening. Goldaks double ellipsoidal model is used for the weld heat source, and inactive element addition technique is used for the addition of weld filler elements. Axial and hoop residual stresses and out-of-plane distortions along the flange face are plotted. In addition, welding start and end effects are discussed.

Modeling the Super Plastic Forming of a Multi-Sheet Diffusion Bonded Titanium Alloy Demonstrator Fan Blade

The paper describes a finite element method in 2D and 3D to simulate the super plastic forming of a demonstrator jet engine fan blade made from Titanium alloy sheet. The fan blade is an assembly of three sheets in which a single inner (core) sheet is diffusion bonded to the two outer (skin) sheets at prescribed zones, which is then super-plastically formed to a desired fan profile. In the model, the diffusion bonded zones between the core and skin sheets are simulated using tied interfaces. The thickness of each skin sheet is not uniform and significant change in thickness can occur over a short distance as well as gradually over the entire skin sheet. The thickness of the core sheet which is smaller than the thickness of each skin sheet remains uniform. The paper describes the design for a scaled-down demonstrator fan blade and model build process. Selected results and evaluations of finite element simulations are presented and discussed.

Microstructure and mechanical properties of Al-1050 during incremental ECAP

Incremental ECAP is a new method of ECAP process were the severe shear deformation is incrementally applied on the sample resulting in grain refining and new texture developing. The fundamental objective of the present work is an observation of effect of different passes of I-ECAP on microstructure and mechanical properties of AA1050 billet. To that end, 8 pass of I-ECAP have been carried out using Bc route and microstructure evolution and mechanical properties of the I-ECAPed samples have been studied. The EBSD and TEM analyses indicates that I-ECAP is as capable as conventional ECAP to grain refinements and a UFG structure is resulted after I-ECAP cycles. Tensile testing and hardness measurements indicates that mechanical properties of the Al-1050 billets increases dramatically by increasing the I-ECAP passes.

Effect of channel angle on the material flow, hardness distribution and process forces during incremental ECAP of Al-1050 billets

Incremental equal channel angular pressing (I-ECAP) is an extension of the classical ECAP method used to produce ultrafine grained (UFG) metals. This paper investigates the first pass of I-ECAP performed on AA-1050 billets measuring 10x10x60mm and the effects of processing with two different dies with the channel intersection angle ϕ=90° and ϕ=120°. The forces required to produce billets were examined and compared. Micro hardness measurements were performed to create a hardness distribution contour map and to evaluate the strain distribution. Moreover FE simulations were performed to investigate the plastic strain distribution within the billets. It was found that using the ϕ=90° die results in higher deformation forces and also greater uniformity of strain distribution when compared to billets processed with ϕ=120° die. The experimental results correlated well with the findings of the simulations.

Effect of Friction and Back Pressure on the Formability of Superplastically Formed Aluminium Alloy Sheet

This paper examines the effect of friction and back pressure on the formability of superplastically formed aluminium alloy AA7475 sheet at the temperature of 517 °C. Several experiments with lubrication and back pressure are performed using a simple box shape tool cavity. The coefficient of Coulomb friction between the formed sheet and tool has been determined indirectly using a finite element model to simulate superplastic forming of the box shape. Typical values determined for all lubricant conditions tested are in the range 0.1 < μ < 0.2. The void growth with strain was determined directly from measurements as a function of back pressure. The results show the application of back pressure at 1 MPa reduces the growth of voids from 7% to 0.3% void volume fraction at a logarithmic thickness strain of 0.65. This paper reports back pressure has a significantly greater role than friction in enhancing the formability of the alloy.

Warm deformation behaviour of UFG CP-Titanium produced by I-ECAP

The objective of the present study is to investigate the deformation behaviour of Ultrafine-grain (UFG) commercial purity Titanium (CP-Ti) at warm temperatures. Firstly, CP-Ti billets were processed through six passes of incremental equal channel angular pressing (I-ECAP) at 300° C using a die channel angle (Φ) of 120°. Uniaxial compression tests were then performed under isothermal conditions on cylindrical samples obtained from the UFG CP-Ti billets. A series of these tests were conducted at different temperatures of 400, 500 and 600 °C and at varying strain rates of 0.01, 0.1 and 1.0 s-1. In each test, the original height of the sample was deformed by ~50% of its original value. The true stress-strain curves obtained, revealed that the flow stress was sensitive to both temperature and strain rate. In general, the flow stress was higher for lower temperatures and higher strain rates. For tests conducted at 400 and 500 °C, the flow stress quickly reaches a peak value, beyond which it exhibits a steady state response where there is no appreciable change in flow stress with increasing strain. The 600 °C tests however shows a strain hardening behaviour. Microstructure of the sample deformed at 600 °C and 0.01 s-1, exhibited significant grain growth.