Desmond Brown

Validation of a Full-Body Computer Simulation of the Golf Drive for Clubs of Differing Length

The aim of the present study was to validate a full-body computer simulation of a golfer’s swing for driving clubs. An elite male golfer performed 24 shots in a laboratory, comprised of 8 trials using each of three drivers of different shaft length (46″, 48″, & 50″). A 5-camera MACTM system operating at 240 Hz collected kinematic data which was subsequently used to drive the model utilising ADAMS/LifeMOD software. Additional skin markers were used for model validation. A large-scale musculoskeletal human model was constructed, with a parametric model of a driver. Inverse and forward dynamics calculations were performed with the imported experimental motion data in order to generate model movement. A commercially available launch monitor recorded experimental eclubhead and launch conditions. There was a very high level of agreement (r=0.995) between experimental kinematic data and the predicted trjectory splines of the model. There was also a high level of correlation (r=0.989) between the model predicted mean values for clubhead speed and the experimental values for each of the club lengths, both demonstrating increased clubhead velocity as club length increased. Muscle contraction force output by the model showed a significant difference (p≤0.001) between driver simulations, demonstrating its capability to illustrate the link between gross muscle force production and club length, as evidenced by the increased force output for the longest shafted club.

The Influence of Cladding on the Springback of 2024-T3 Aluminium Alloy

Double curvature nacelle skin components are often produced in 2024-T3 Alclad aluminium alloy (clad both sides), using simple stretch forming. For this process uniaxial-tension is assumed to be the dominant mode of deformation. The observed springback in these components is generally minimized by inducing high levels of strain within the forming limits of the material. Experimental investigations to quantify the level of the springback have revealed an underlying aspect of material behaviour, which to the authors’ knowledge, has not been reported elsewhere. The results of this investigation have shown a remarkable dependence on specific material parameters unique to the Alclad material. Whilst previous investigations [1, 2, 3] have shown the influence of cladding, it has been assumed that cladding layers on both sides produce effects that are symmetrical about the mid-plane of the sheet. However, the current investigation has revealed a distinct asymmetry in springback behaviour. A detailed study of cladding thickness and strength, residual stresses and through-thickness material property changes has revealed that this asymmetry results from a complex combination of these parameters.

Structural and Frictional Performance of Fused Deposition Modelled Acrylonitrile Butadiene Styrene (P430) with a View to Use as Rapid Tooling Material in Sheet Metal Forming

Using additive layer manufacturing techniques, such as Fused Deposition Modelling (FDM), it is possible to produce complex geometry relatively quickly and cheaply. For this reason these processes offer intriguing possibilities for tooling in metal forming processes. A common material utilised in the FDM process is Acrylonitrile Butadiene Styrene (ABS). A series of compression and tensile tests were carried out on FDM ABS test specimens built in a range of orientations. The tensile tests were carried out until fracture and the specimen cross-sections analysed to investigate the cause of failure. In uniaxial tension the vertical build direction was found to be the weakest, failing in a brittle fashion. The FDM material elastic modulus and Poisson’s ratio were found to be isotropic in nature within experimental scatter. The ‘yield’ strength in compression was found to be higher than that observed for equivalent tensile orientations. Following a series of strip pull friction tests using commercially pure titanium as the blank material, it was found that without the utilisation of an interfacial lubricant a favourable frictional performance was achievable on ABS tool surfaces. Due to tool wear however, the frictional performance of these tool pieces deteriorated with increasing sliding distance.

The Influence of Strain Rate on the Springback of Commercially Pure Titanium in a Stretch Forming Operation

A common processing stress state used in the construction of sheet metal components is that of uniaxial tension/stretching. This work examines the stretching of CP-Ti over a rigid form tool using varying degrees of strain and strain rate. The degree of springback is shown to be influenced by the interaction of strain rate, strain magnitude and time following forming.

Profile Correction of a Stretch Formed Aluminium Alloy during Artificial Ageing

A method of springback reduction is presented which involves a combination of solution heat treatment, natural ageing, stretch forming and artificial ageing. A commercial aluminium alloy, 2219-O Hi-Form, is solution heat treated and subjected to two pre-form natural ageing periods of one and seven hours before the stretch forming process. Following the forming process an artificial ageing process combined with creep age forming techniques is used. Springback is assessed following the stretch forming and artificial ageing processes. This process is shown to provide a controlled means of correcting the springback following stretch forming.

Modelling the Effect of Pre-Strain and Inter-Stage Annealing on the Stretch Forming of a 2024 Aluminium Alloy

The severe double curvatures often encountered in aerospace fuselage and nacelle skins often necessitate multistage stretch forming operations. Each stage adds value to the component and rejection, particularly at later stages, must be avoided. Therefore process optimisation using accurate modelling tools to predict the strain levels is essential. This paper presents a novel method for modelling the aforementioned stages of the process using a tailored material model based on strain history and heat treatment. The modelling process is implemented within the PAMSTAMP Finite Element code, by modifying the material properties in the input file using an Excel based algorithm. The proposed method is validated using profiled stretch formed specimens, thereby imposing a variable strain gradient in a single specimen without having to resort to the complexity of double curvature. The model results are shown to represent the observed behaviour well.

Double Curvature Springback in Stretch Formed 2024-T3 Aluminium

A test rig was developed to investigate springback in stretch draw forming processes, which are considered to be nominally uniaxial. An interchangeable tool allows the examination of both single and double curvature surfaces. Two double curvature tools with the following radii were used in the experiments, (A) 200mm by 450mm and (B) 450mm by 200mm. The first radius in each case corresponds to the direction of stretch. Obviously the smaller radius results in a larger moment, which creates a negative springback in the orthogonal direction. This effect is more pronounced in tool (A) due to the higher tensile strain levels in the direction of stretch directly affecting the strains in the orthogonal direction. By considering the resultant moment in each axis of the sheet independently, an analytical method was devised to give an approximation of the springback profile. Overall the analytical data correlates well with both experimental and Finite Element (FE) results.

The Influence of Strain Rate Variations on the Appearance of Serrated Yielding in 2024‐T3 Al‐Clad Aluminium Alloy

To avoid failure during the stretch forming process using manual control, machine operators tend to achieve the final form using a stop‐start approach. It was observed that when approaching full form, stretcher‐strain marks appeared on the surface of the part if the operator stopped and restarted the forming operation. In order to investigate this phenomenon, a series of tensile tests was conducted using two batches of 2024‐T3 aluminium alloy. The specimens were tested using several different strain rates, representative of those used on the shop floor. Additional tests were conducted involving a series of pauses under displacement control at differing levels of strain and strain rate. In the uninterrupted tests for the two batches of 2024‐T3 material tested, serrated yielding was observed just prior to failure. However for the tests in which there was a pause in displacement, the material consistently exhibited serrated yielding when the crosshead began to move again. These results indicate that the pause provides an opportunity for strain ageing and pinning of the dislocations resulting in serrated yielding of this alloy. In order to avoid serrated yielding, stretch forming operations using 2024‐T3 aluminium should be conducted at a constant strain rate without interruption. This also has far reaching implications for those involved in the production and testing of these alloys. The test programme described represents an initial attempt to investigate a phenomenon noted during an industrial forming process and should be extended to analyse the affect of strain path changes on the occurrence of serrated yielding.

The influence of uniaxial prestrain on biaxial r‐values in 7075‐O aluminium alloy

Biaxial test methods have been used to determine, not only yield behaviour under biaxial conditions, but also the strain response. This paper examines the influence of uniaxial prestrain upon the biaxial r‐value by extending the disc compression test procedure proposed by Barlat et al. [1]. The extension involved the use of digital image measurements of in‐plane strains. The material examined was a 7075‐O condition aluminium alloy. The results of the experimental programme indicated that the biaxial r‐value is unaffected by uniaxial prestrain. When using the disc compression test, the mode of deformation and therefore the biaxial r‐value were found to be very sensitive to the prevailing friction conditions.

The Influence of Through-Thickness Material Property Variation on Stretch Forming Springback

Stretch forming is commonly used in the manufacture of low-volume convex aircraft panels. The gentle curvature and high degree of stretch leads to relatively low levels of elastic recovery post forming. Previous investigations [1] have shown that there is a large difference in the measured springback depending upon which side of an Alclad aluminium sheet is in contact with the tool surface. Initial investigation into the clad layer properties revealed no accountable variation in either thickness or strength. Instead the asymmetric springback behaviour was attributed to material property variations through the alloy core of the sheet. An analytical method for the prediction of the asymmetric springback incorporating the through thickness property variation is presented. Material strengths at specific through thickness positions were determined using a procedure based on residual strength measurements. The predicted results correlate well with the experimental data, which had initially demonstrated the asymmetric springback