No abstract

No abstract

Purpose The purpose of this paper is to investigate the effect of fastener geometry (protruding head and countersunk fastener) and friction coefficient on the stress distributions around the hole of the double-lap single bolted aluminium alloy joints. Design/methodology/approach 3D finite element analyses of double-lap bolted 7075-T6 aluminium joints were carried out. An elastic-plastic multi-linear kinematic hardening material behaviour was assumed for the Al alloy. Contact was defined using an augmented-Langrange contact algorithm, including the friction effect. Bolt clamping force and remote axial tensile loading were applied in two load steps and their separate and combined effects on the joint behaviour were investigated for two types of fastener configurations. Findings It was observed that bolt clamping reduces the axial tensile stress at the hole edge by introducing a through-thickness compressive stress. This reduction in stress concentration may have a beneficial effect on the fatigue life of the joint. Second, bolt clamping reduces the bearing stress at the fastener hole by creating a frictional force between the joint plates. Results showed that the joint with protruding head fastener shows lower tensile stress concentration, and lower bearing stress, near the bolt hole of the middle plate. Originality/value Bolt clamping force reduces both the stress concentration near the hole edge and the bearing stress at the hole by creating a frictional force. Joint with a protruding head fastener may lead to higher load carrying capability and improved fatigue life. Friction coefficient affects the stress levels around the bolt hole.

Fire power for a main battle tank is one of the most important performance parameters like survivability and mobility. Fire power effectiveness is directly related to the first shot hit probability, performance of main gun, second armament, gun and turret drive system, fire control system, automatic target tracker, commander and gunner sight etc. First shot hit probability (a measure of cumulative effects of errors) is affected by the variations of the projectile parameters, the main gun structure uncertainties, fire control system errors, interaction between the projectile and the gun barrel and the unpredictable environmental changes. These errors and variations can be eliminated or minimised by understanding and simulating the firing event properly, manufacturing the related parts in high precision, using advanced fire control algorithms, and accurate sensors. In this review study, the effects of main gun structural components on the first shot hit probability are investigated taking into account all of the associated error sources. In order for a main battle tank to have both high and repetitive first shot hit probability under all battlefield conditions the gun structure should respond in a similar manner in successive firings without causing any abrupt change in performance. In this study, first the dynamic behaviour of gun/projectile system is discussed and then the design recommendations for the main gun components such as bearings, gun barrel, recoil system etc. to achieve higher first shot hit probability are reviewed.

Main battle tanks constitute one of the most powerful fire powers for the armoured land forces. To use this very high fire power efficiently, the dispersion of shot impacts becomes crucial. Dispersion is affected by the aerodynamic factors, gun-projectile interactions, projectile and gun dependent factors, manufacturing tolerances and environmental factors. The change in aerodynamic factors and environmental conditions varies the aerodynamic forces applied on the projectile and this affects the dispersion characteristics of the projectile. In this study, the effects of the changes in recoil stiffness, gun support stiffness, projectile muzzle velocity and manufacturing tolerances of projectile forward/rear bourrelet diameters on the dispersion for 120 mm L44 and L55 calibre guns are investigated. Armour piercing fin stabilised discarding sabot type projectile is used in the analysis. Statistical dispersion analyses including interior ballistic, in-bore balloting and exterior ballistic analyses are conducted using PRODAS ballistic software. According to the results, it is determined that the decrease in projectile/bore clearance (forward/rear bourrelet diameter) results in improved dispersion of ammunition. The 10% changes from the nominal recoil stiffness and the vertical support stiffness values have negligible effects on the dispersion. In addition, the results show that muzzle velocity variations influence the dispersion in vertical direction substantially. Using the procedure applied in this study, it is shown that different clearance conditions can be analysed and most suitable tolerances may be determined taking into consideration of both the gun system performance and manufacturability.

Bu çalışmada, cıvata bağlantılı tabakalı kompozit levhalarda çekme mukavemetini yüksek hassasiyette belirleyebilmek amacıyla kademeli hasar ilerleme modeli kullanılarak hasar analizi uygulanmıştır. Hasar ilerleme modeli ANSYS APDL kullanılarak hazırlanmıştır. Hashin hasar kriterleri kullanılarak sonlu elemanlar analizleri gerçekleştirilmiştir. Çalışmanın sonuçları deneysel çalışma sonuçları ile kıyaslanmış ve oldukça benzer sonuçlara ulaşılmıştır. Ayrıca levha genişliği/delik çapı oranı (W/D) 2'den 4'e kadar, kenar uzaklığı/delik çapı oranı (E/D) ise 1'den 4'e kadar değiştirilerek geometrik etkilerin kompozit yapının yük taşıma kapasitesine etkisi araştırılmış ve maksimum çekme dayanımları hesaplanmıştır. W/D ve E/D oranları 2 için hasar levhanın serbest kenarına doğru kayma (yırtılma) şeklinde ilerlemiştir. W/D ve E/D oranları 2'den büyük olduğunda hasar ezilme (yatak hasarı) şeklinde gerçekleşmiştir. [02/902]s konfigürasyonuna sahip kompozit levhada net çekme hasarı meydana gelmemiştir. W/D ve E/D oranları 3 olduğunda kompozit levha maksimum yatak (ezilme) mukavemetine ulaşmaktadır.In this study, in order to determine the tensile strength of bolted laminated composite plates with high fidelity, failure analyses were performed by applying progressive damage model. Progressive damage finite element model was built using ANSYS APDL. Finite element failure analyses were performed using Hashin's failure criteria. Results of the present study were compared with the experimental data and very consistent results were obtained. Additionally, changing the plate width/ hole diameter ratio (W/D) between 2-4 and edge distance/hole diameter ratio (E/D) between 1-4, the effects of geometric parameters on the load carrying capacity of the composite plate were investigated and maximum tensile failure loads were determined. For W/D and E/D ratios equal to 2, failure propagated towards the free end of the plate showing shear failure mode. For W/D and E/D ratios greater than 2, bearing failure mode occurred. For [02/902]s configuration no nettension failure mode occurred in the composite plate and for W/D and E/D ratios equal to 3 maximum bearing strength was achieved.

No abstract