A novel manufacturing process and validated predictive model for high strength and low residual stresses in extra large 7xxx panels

A novel manufacturing process, enabling the production of high quality i.e. with low and controllable residual stress RS distributions and good mechanical properties T section 7xxx panels, has been established. This process provides a solution to residual stress induced distortion problems, which greatly concerns a range of industries, especially the aircraft industry. This process consists of three sequential steps water quenching WQ , cold rolling CR and constrained ageing CA . The effectiveness of this process was experimentally verified through applying this process to laboratory sized 7050 T section panels. The RS was measured by neutron diffraction and X ray techniques, in addition to deflections and hardness at each processing stage. An integrated Finite Element FE model, including all three steps, was developed to simulate this manufacturing process and predict both the RS and the final strength distributions. It has been concluded that this novel process can effectively reduce the residual stresses from 300 amp; 8239;MPa to within 100 amp; 8239;MPa and produce T section panels with required mechanical properties i.e. hardness 159 amp; 8239;HV10 . A cold rolling level of 1.5 was found most appropriate. The residual stress and yield strength distributions were accurately predicted by FE, providing a valuable prediction tool to process optimization for industrial application

Residual Lattice Strain and Phase Distribution in Ti 6Al 4V Produced by Electron Beam Melting

Residual stress strain and microstructure used in additively manufactured material are strongly dependent on process parameter combination. With the aim to better understand and correlate process parameters used in electron beam melting EBM of Ti 6Al 4V with resulting phase distributions and residual stress strains, extensive experimental work has been performed. A large number of polycrystalline Ti 6Al 4V specimens were produced with different optimized EBM process parameter combinations. These specimens were post sequentially studied by using high energy X ray and neutron diffraction. In addition, visible light microscopy, scanning electron microscopy SEM and electron backscattered diffraction EBSD studies were performed and linked to the other findings. Results show that the influence of scan speed and offset focus on resulting residual strain in a fully dense sample was not significant. In contrast to some previous literature, a uniform and Ti phase distribution was found in all investigated specimens. Furthermore, no strong strain variations along the build direction with respect to the deposition were found. The magnitude of strain in and phase show some variations both in the build plane and along the build direction, which seemed to correlate with the size of the primary grains. However, no relation was found between measured residual strains in and phase. Large primary grains and texture appear to have a strong effect on X ray based stress results with relatively small beam size, therefore it is suggested to use a large beam for representative bulk measurements and also to consider the prior grain size in experimental planning, as well as for mathematical modellin

Use of Symmetry for Residual Stress Determination

Instrumental and certain sample characteristics can affect the detected Bragg peak shifts which are not related to the strain being measured. Three major effects can influence the measurement the surface effect, where the instrumental gauge volume IGV is not fully immersed at a surface or interface, the grain size effect where there is random positioning of large grains in the sample within the gauge volume and the relative shift in position of the centre of gravity of measurement due to absorption of neutrons. All of these effects can be reduced eliminated by making pairs of neutron diffraction measurements 180 degrees to each other at the same location. Results are presented from a round robin benchmark weldment, denoted TG6, from the European Network on Neutron Techniques Standardization for Structural Integrity NeT . This is made from a nickel alloy which has large grains and strains and has a high neutron attenuation coefficien

Looking Towards the Future of Strain Scanning Using Neutron Diffraction

All aspects of instrument control, data acquisition, simulation and analysis are expected to merge in the future. For instance real time data analysis will feed back influencing the instrument control in order to optimize the measurement time and simulations themselves will control the instrument. This presentation will discuss how the all important pre planning of a measurement can be optimized and used to define the whole measurement, efficiently and effectively using the neutron beamtim

Influence of low magnitude plastic strains on residual stress in 7075 aluminium alloy

The effect of post quench delay on residual stress has been determined by subjecting four rectilinear blocks of quenched 7075, containing large residual stress magnitudes, to small lt;1.0 plastic strains applied by cold compression. One experiment kept the plastic strain the same in all samples amp; 8764;0.12 by cold compressing simultaneously in one pressing. The second pressed the blocks separately to the same strain amp; 8764;0.45 . The post quench delays were lt;10, 60, 120 and 240 min. The residual stresses were characterised using neutron and X ray diffraction. It was possible to detect the impact of the small plastic strains on all samples, but the diffraction measurement techniques could not conclusively isolate the influence of the post quench dela

NET TG1 Residual stress analysis on a single bead weld on a steel plate using neutron diffraction at the new engineering instrument STRESS SPEC

Non destructive analysis of phase specific residual stresses and textures is only possible by diffraction methods. The new neutron diffractometer STRESS SPEC was installed at FRM II in Munich, Germany, for this purpose. It is designed to be equally applied to texture and residual stress analyses by virtue of its flexible configuration. The results of measurements on a single bead on plate weld within the framework of the European Network on Neutron Techniques Standardisation for Structural Integrity NET are presented here, in order to demonstrate the reliability and accuracy of the instrument by comparing previous results from other neutron diffraction facilities by using a Bayesian statistical approac

Emphasizing the accuracy of the uncertainty of residual stress determination using neutron diffraction

AbstractThe execution of residual strain measurements using neutron diffraction in order to determine the residual stress state in a material or component is now a well-established method. The analysis of the uncertainty of the resultant strain and stress is a topic that is frequently brought into discussion. There are many sources, some obvious and some not so obvious that can contribute to the overall uncertainty and each should be considered carefully. The potential uncertainties could be simulated using a model that closely represents the experimental set-up and the particular sample that is being measured. A suggested form could be the use of a finite element model of the sample within one of the many neutron scattering simulation programs. The interaction between the properties of the sample and the instrument and/or set-up that is measuring the strain is something that can vary substantially. Taking this into account, the accuracy of the final uncertainty of the measurement is revisited and reassessed in this discussion

Improving Beamtime Efficiency for Residual Stress Neutron Experiments

Starting during the shut down of the HZB research reactor BER II in 2011 2012 the E3 residual stress and texture diffractometer in Berlin underwent a comprehensive upgrade. The investments were broken down into different criteria, such as enhancing the instrument performance and accuracy as well as extending the range of applications for the user community. Here, we report about the gains achieved after integrating and commissioning the individual hardware and software tools included in the upgrade project, namely a motorized primary slit to accurately adjust the gauge volume, a secondary optics radial collimator and a laser scanner to precisely and quickly align the sample. The integration of the presented devices is further supported by software developments to shorten the instrument alignment procedure and measurement time. The upgrade has improved the efficiency of the available neutron beamtim