Adding material in highly stressed areas can also help redistribute stress to minimise the stresses experienced. For the purpose of reducing weight Kevlar , glass fibre and carbon & epoxy composite materials are used to make the bicycle frames nowadays. That said, a crash that destroys a carbon frame is likely to destroy most other frames as well. It is usually possible to bend frames back into alignment and repair damage. Figure 4.1: Common bicycle frame materials The materials used for mountain bicycle frames have a wide range of mechanical properties. Doing this, doubling the diameter results in four times the stiffness. Frame And Fork Materials: Fine frames are built from a myriad of materials. One of the unique abilities of carbon fibre is its ability to damp vibration. Steel and titanium have a fatigue limit, a maximum stress below which the material can be loaded an unlimited number of times without failing. Cycling companies will often talk about using aerospace grade metals – but the reality is that designated alloys have to conform to certain quality requirements regardless of whether they are used in an aircraft or a bike frame. Their properties are dependent on the direction of load. However steel is “density challenged” – frames are usually heavier than their aluminium or titanium equivalents. Nonetheless, aluminium is a more brittle and weaker material than steel, and as such frames tend to be slightly overbuilt to make frames stronger and give a larger safety margin. off-road.cc Editorial and general enquiries: info@off-road.cc This study examines the Al6061 aluminum alloy as the material for the bicycle frame. Do you need the marginal gains that a lightweight carbon frame can provide, do you want the lightweight but cheaper compromise of aluminium, do you want the prestige and life-long durability of titanium, or do you want the traditional and versatile steel? The quality of the layup is very important, with poor bonding between layers in the laminate causing significant weakness. However, aluminium has no limit and given enough loading cycles, will fail under very small stresses. There's a lot of myths, marketing hype and dubious 'engineering' talk surrounding frame materials. Assembling thin walled tubing also becomes difficult to assemble, with heat from welding affecting heat-treatments and reducing strength in the weld area. There is significant interest to improve the impact resistance of carbon fibre by modifying the resin and fibres as well as using novel layups and resins. ing bike frames. That doesn't mean you should listen to people who claim aluminium frames are much more prone to failing in the real world however; by designing frames to minimise the maximum stress levels experienced, the lifetime of the frame will be more than long enough to cover a normal lifetime of use. There is little doubt that a carbon frame can be made the lightest, so it wins, assuming you just go by the numbers. It is more difficult to find butted titanium tubing, though as its popularity increases manufacturers provide more and more options. For a given amount of material (and weight), we can increase the diameter of a frame tube but must simultaneously reduce its thickness. By designing a frame to be stiff enough, it will also usually be strong enough to withstand cycling loads. An obvious example is the beefed up bottom brackets designed to resist flexing during pedalling. CFRP has incredible strength and stiffness for its weight, allowing very lightweight frames to be built. In theory, with thin enough tubing, it would be possible to build a frame with weight on-par with the lightest frames today. It is possible to make an excellent frame with any of the materials mentioned, but for a high performance frame, the choice will usually come down to  be either carbon fibre or aluminium. Materials selection of a bicycle frame using cost per unit property and digital logic methods January 2010 International Journal of Mechanical and Materials Engineering 5(1):95-100 Read more: 15 of the best steel road bikes and frames. Elasticity: When an object responds to bending or stretching by returning to its original shape, it is said to have a high level of elasticity. You can download the paper by clicking the button above. What material properties are important in choosing bicycle frame material? Thorough damage assessment on carbon frames is significantly more complicated. CFRPs allows reinforcement of the frame by adding more material in specific areas. 17 Comments. alloy—frame, foam—helmet, etc). Contrary to what you might expect, outright strength is less important. This is why we now see aluminium bikes with the oversized tubes that are needed to give the required stiffness to the frame. Whilst a metal will bend before failing completely, when carbon reaches its strength limit, it will fail suddenly. They can withstand tension, but would crumple if compressed. However many manufacturers do offer crash replacement programmes. Fibre orientation can be modified to favour stiffness or compliance for more race or comfort focussed frames. One table will present material properties requirements for the selected materials commonly used for bicycle wheels, frame, components and helmet. The sheets are cut to shape and layered around a core. Manufacture quality control is essential. 3Al-2.5V is the most widely used alloy, though the higher performing 6Al-4V also exists. This provides stiffness in one direction but compliance in the other. We don’t use pure iron (steel is a mixture of iron and carbon), pure aluminium or pure titanium. Typical frame weighs from 1,5 by 3,0 kg, which is about a quarter of the weight of the bicycle. Alloys are metals with other elements added to improve properties like strength or stiffness. There will be a further designation indicating the tempering process – often T6 – the alloy has gone through. As tubing diameter increases, so does its stiffness. The mechanical pro-perties of common bike frame materials are listed in Table 1. It is relatively hard to work with, wearing out tooling more quickly and requiring a controlled atmosphere for welding. Carbon fibre It is quite natural to be so, since poor quality steel is an obsolete material (however the story is radically different with hi-quality steel), carbon can be expensive sometimes and titanium is not so easy to find. This is then placed inside a mould and cured at high temperature and pressure. Although over the years there have been such oddities as bamboo and plastic frames, current road bikes are made of one or blends of these four materials: steel, aluminum, titanium and carbon fiber. It's worth noting that it's often how the chosen material is used by the engineers and manufacturers that matters most, and this is something that each brand will typically play with. This material is currently being used all over the bicycle market, from strictly track bikes to road racers, complete frames or part CFRP frames, and components used in mountain bike off road frames. In the event of a crash or damage there is a significant threshold in which steel can deform before failing. The fibres have diameters down to 5 micrometres, much thinner than a human hair. Fluid is run through at incredibly high pressure forming the tube to the shape of the mould it is in. Instead, additional elements are added to improve the basic properties of the metal. It can be made to have very high strengths. Carbon or high-tensile steel is a good, strong, long-lasting steel, but it isn't as light as its more high-tech brother, the steel known as chromoly. Comfort and frame design are perhaps something we will leave for another day. Production frames are of course available, but these materials are also the purview of custom builders who will design a bike fitted to you. The material that frame is made out of has a dramatic effect on the way it rides, its durability, and cost. However, nowadays the ride of an aluminium frame can be exceptional. Failure of titanium frames, like most steel, is incredibly rare, so this is a bike that will surely stand the test of time. Best mountain bikes you can buy for under £2,000, The best hardtail and full suspension mountain bikes you can buy for under £1500, Best MTB's that you can get shipped straight to your door, The best titanium gravel and adventure bikes you can buy, No, longer mountain bike geometry isn't a fad, First Look: Pipedream Full Moxie Frameset, MT Zoom Ultralight Inline Carbon Seatpost review, Maxxis Shorty 3C Maxx Terra EXO TR tyre review, The best gravel wheelsets you can buy in 2021. In contrast metals act like springs and have no significant damping. The materials used for bike frames have a wide range of mechanical properties. Different steel alloys, such as niobium, mangaloy and of course stainless, are also used. This allows the dimensions and geometry of the tubing to be tailored to provide certain ride characteristics and can also help redistribute stresses in the frame. Abstract ² The bicycle frame is the main structure in a cycle to support the external loads acting on it. The metallic properties of ductile materials, the von Mises stress and strain analysis, and optimal design theory are used. Different frame materials have different properties that give them slightly different characteristics, but you simply cannot know how a bike will ride by its frame material. I for one, was glad to be able to reattach rack mounts during a bikepacking expedition - not something that is as easy with other materials. CFRP consists of microscopic carbon fibres aligned and held in a resin matrix. It is potentially more difficult to identify damage with a carbon frame – where a metal frame will have bent, a carbon frame may have cracks that may not be visible. Metals are isotropic, meaning their mechanical properties are the same in all directions. Advertising and commercial: sales@off-road.cc, Mountain bike, bikepacking and gravel bikes. Titanium is a highly desirable material due to its fabled ride quality, supple and bump-absorbing. Unfortunately it is the case that you get what you pay for, and a carbon frame will be more expensive than a metal equivalent. Indeed on some frames it is possible to visibly squeeze the tube walls together. The modulus of the epoxy resin is extremely low, resulting in a brittle material; which consequently affects the method of which the CFRP layers are applied. Modifying the resin properties can also be used to improve these properties. It is incredibly strong, very stiff, easy to work with and cheap to manufacture. The resin must be cured to set the shape of the composite. Reviews, buying advice and news. All material © Farrelly Atkinson (F-At) Limited, Unit 7b Green Park Station BA1 1JB. Carbon fibre, or more properly Carbon Fibre Reinforced Polymer (CFRP), is the new kid on the block. However titanium genuinely provides a frame for life. RTM arguably gives even better control over localised material properties, and can lead to overall higher quality carbon fibre parts. You can’t compare the reputation of a material as it’s used in a mass produced frame with a custom application because mass produced frames haven’t been optimized to meet your unique priorities. deflect under load providing additional comfort. While as an element titanium is very abundant, it takes a lot of effort to refine and process into the tubing used for frames. All of this drives up its cost significantly. This has much more to do with frame geometry affecting how forces are transferred to the rider. Hydroforming is used with aluminium tubing to form complex shapes. However, the lower density will result in a frame weighing around 30% less than a steel frame. To browse Academia.edu and the wider internet faster and more securely, please take a few seconds to upgrade your browser. A frame may use hundreds of individual pieces. The core is commonly a removable inflatable bladder which applies internal pressure during the cure. In the past material and production limitations restricted the minimum wall thickness achievable with steel. Some steels, such as 853 by Reynolds actually increase in strength after cooling due to the way they have been treated. Young’s Modulus is similar for metals made from the same alloy. The way this is done is know as the layup. There is an amazing amount of folkloric "conventional wisdom" about bicycle frames and materials that is widely disseminated, but has no basis in fact. Aluminium alloy is nowhere near as strong or stiff as steel, but has around one-third of the density. It is completely different because it can be “designed” specifically for its application. At the very core of every bicycle, there is a frame. At the end of the day you have to choose where your priorities lie. Discussing the intricacies of this is something that could take up a whole additional article. It is incredibly hard-wearing and corrosion resistant, which is also why it is often left unpainted. Instead tubes are modified mechanically. Whilst explaining this is outside the scope of this article, this is a heat treatment that improves the properties of the alloy. There is not one material in the table that has advantageous properties in each category, which explains why manufacturers continue to fabricate frames from several different materials. Welds can act as stress concentrators and nowadays, many high-end alloy frames, such as the Cannondale CAAD series, smooth out the weld area to avoid any localised stress concentration. A tube “blank” is put inside a die. Usually, Grade 9 Titanium is used for bike frames. Nonetheless, aluminium is a more brittle and weaker material than steel, and as such frames tend to be slightly overbuilt to make frames stronger and give a larger safety margin. Frames are designed so that stresses are low enough that in normal loading it will not reach its fatigue life within its usage lifetime. High modulus carbon can be used to stiffen key area. The excessive use of more material to reinforce frames resulted in stiff frames before designs became more refined. Failure is very unlikely but when it does happen is likely to be catastrophic. Buy steel because you want a bespoke frame or favour a smooth ride quality and don’t mind a bit of extra weight. First, there are three types of material properties: Physical – Density, color, electrical conductivity, magnetic permeability, and thermal expansion. Several properties of a material help decide whether it is appropriate in the construction of a bicycle frame: Density (or specific gravity) is a measure of how light or heavy the material per unit volume. There's likely to be no difference between a bike that claims to be made from 'military grade' material and one that isn't. While it is possible to repair carbon fibre, it could be difficult to do satisfactorily without knowing the (proprietary) details of the layup of the frame to be repaired. Each bicycle frame material offers a list of differing characteristics that will affect the cost, comfort, weight, stiffness, strength and durability. In 1897 Alfred M. Reynolds took out his patent on butted steel bicycle tubes and, for steel aficionados, a frame bearing the Reynolds stamp is a must have to the present day. It means that, unlike with metal, a frame tube can have different characteristics along its structure. In this project the bicycle frame Carbon frame ride can be controlled in much more detail by varying the layup in different areas of the frame to tailor for compliance or stiffness. It resists loads in all directions. When a bicycle maker chooses a material to make a bike frame, he or she usually considers the following properties of the material. Academia.edu no longer supports Internet Explorer. What Makes Titanium the Cyclists 'Dream Material'? Table two will display these common possible materials to be used, in reference to their application (i.e. By “rubberising” the resin, it can absorb more vibration. 2009 ASME Human Powered Vehicle Competition Drexel University Philadelphia PA DESIGN REPORT Olin College Human Powered Vehicle Helios CONTENTS, Embedded systems training in bangalore .docx, THE ENERGY APPROPRIATE PERSONAL COMMUTER VEHICLE, MECHANICAL ENGINEERING DESIGN II: Product Development Project, Electrical Scooter (Mechanical Engineering Design 1 UiTM). On the other hand CFRPs are anisotropic. The key advantage of carbon fibre is that layups can be tailored to achieve specific ride properties. In other words there should usually be significant warning and visible bending before a steel frame will fail completely. This is then impregnated with resin under a vacuum and cured. Less dense than steel but heavier than aluminium, it also falls roughly in the middle in terms of stiffness. Aluminium road bikes – save for some custom designs – are fairly inexpensive. The excessive use of more material to reinforce frames resulted in stiff frames before designs became more refined. An aluminium frame will use more than twice the volume of material as steel. Wall thicknesses are around twice that of steel and tubing diameters are around 20-30% larger to maintain suitable stiffness. However frames can be designed to be compliant, i.e. Steel will rust if neglected – though frames can be treated and manufacturers such as Reynolds produce stainless tubing that largely negates this problem. Butted tubing, tubing with variations in the wall thickness along its length makes welding easier whilst maintaining thin walls. However material toughness is essential in ensuring damage resistance. Bicycle frame design is about selecting tubing dimensions to appropriately tailor the stiffness and compliance to the desired ride characteristics. There is no material in the table that has advanta-geous properties in each category, which explains why manufacturers continue to fabricate frames using sev- Most manufacturers now use pre-preg carbon; sheet of carbon fibres that are pre-impregnated with resin. It's worth noting that it's often how the chosen material is used by the engineers and manufacturers that matters most, and this is something that each brand will typically play with. There are two main aluminium alloys in use in the bike industry today – 6061 and 7005. However, there is a limit to how thin tubing walls can be made before they become susceptible to damage, denting and more importantly buckling. The ability to repair steel can often be overlooked. The earliest bikes were simple wooden framed push along affairs but soon the material of choice was heavy iron, which in turn was superseded by steel. For example Kevlar and Vectran are used to provide additional crash resistance. However, nowadays the ride of an aluminium frame can be exceptional. Frames tended to be overbuilt in weld areas to avoid cracking due to fatigue. A tougher material is able to absorb more energy before failing, meaning it will bend rather than breaking in a brittle way. Weight, or rather the frame weight, It depends on the density of the material and, of course, frame structure, in particular, its thickness pipes. Each bicycle frame material offers a list of differing characteristics that will affect the cost, comfort, weight, stiffness, strength and durability. The sheets must be built up in multiple layers - forming a laminate - placed at different angles to withstand different loading directions. High end mountain bikes also take advantage of carbon, and here it is again a wonderful frame material. Because carbon fibers are pliable in one direction and stiff in the other, sheets can be layered to make different parts of the frame react differently. 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