Synthetic structural materials with exceptional mechanical performance suffer from either large weight and adverse environmental impact (for example, steels and alloys) or complex manufacturing processes and thus high cost (for example, polymer-based and biomimetic composites) Natural wood is a low-cost and abundant material and has been used for millennia as a structural material for building and furniture construction However, the mechanical performance of natural wood (its strength and toughness) is unsatisfactory for many advanced engineering structures and applications Pre-treatment with steam, heat, ammonia or cold rolling followed by densification has led to the enhanced mechanical performance of natural wood However, the existing methods result in incomplete densification and lack dimensional stability, particularly in response to humid environments, and wood treated in these ways can expand and weaken Here we report a simple and effective strategy to transform bulk natural wood directly into a high-performance structural material with a more than tenfold increase in strength, toughness and ballistic resistance and with greater dimensional stability Our two-step process involves the partial removal of lignin and hemicellulose from the natural wood via a boiling process in an aqueous mixture of NaOH and Na2SO3 followed by hot-pressing, leading to the total collapse of cell walls and the complete densification of the natural wood with highly aligned cellulose nanofibres This strategy is shown to be universally effective for various species of wood Our processed wood has a specific strength higher than that of most structural metals and alloys, making it a low-cost, high-performance, lightweight alternative

https://www.fpl.fs.fed.us/documnts/pdf2018/fpl_2018_song001.pdf

Processing bulk natural wood into a high-performance structural material

Reducing human reliance on energy-inefficient cooling methods such as air conditioning would have a large impact on the global energy landscape. By a process of complete delignification and densification of wood, we developed a structural material with a mechanical strength of 404.3 megapascals, more than eight times that of natural wood. The cellulose nanofibers in our engineered material backscatter solar radiation and emit strongly in mid-infrared wavelengths, resulting in continuous subambient cooling during both day and night. We model the potential impact of our cooling wood and find energy savings between 20 and 60%, which is most pronounced in hot and dry climates.

/pdf/a-radiative-cooling-structural-material-18m9j9z5y8.pdf

A radiative cooling structural material.

Although steel has been the workhorse of the automotive industry since the 1920s, the share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1 per cent in 1995 to 60.1 per cent in 2011 (refs 1, 2). This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials. Recently, high-aluminium low-density steels have been actively studied as a means of increasing the specific strength of an alloy by reducing its density. But with increasing aluminium content a problem is encountered: brittle intermetallic compounds can form in the resulting alloys, leading to poor ductility. Here we show that an FeAl-type brittle but hard intermetallic compound (B2) can be effectively used as a strengthening second phase in high-aluminium low-density steel, while alleviating its harmful effect on ductility by controlling its morphology and dispersion. The specific tensile strength and ductility of the developed steel improve on those of the lightest and strongest metallic materials known, titanium alloys. We found that alloying of nickel catalyses the precipitation of nanometre-sized B2 particles in the face-centred cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. Our results demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels for structural applications and others.

Brittle intermetallic compound makes ultrastrong low-density steel with large ductility

Recent advances in the development of aerospace materials

Strengthening mechanisms, deformation behavior, and anisotropic mechanical properties of Al-Li alloys: A review

Recent developments in advanced aircraft aluminium alloys

A review on the gun barrel vibrations and control for a main battle tank

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.

https://publications.drdo.gov.in/ojs/index.php/dsj/article/download/12246/6187

Effects of Tank Gun Structural Components on the First Shot Hit Probability

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.

https://publications.drdo.gov.in/ojs/index.php/dsj/article/download/14922/7255

Effects of Projectile and Gun Parameters on the Dispersion

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.

Tolga Dursun

Papers

Recent developments in advanced aircraft aluminium alloys

A review on the gun barrel vibrations and control for a main battle tank

Effects of Tank Gun Structural Components on the First Shot Hit Probability

Effects of Projectile and Gun Parameters on the Dispersion

A finite element analysis of bolted joints loaded in tension: protruding head and countersunk fastener