Materials Selection Assignment

Transcription

1 PDES1155 Materials Technology Materials Selection Assignment Ice Axe James Higson 12/4/2012

2 Description and Design Requirements HEAD TIP SHAFT Classic (Walking) Ice Axe 1 Page 1 Climbing Ice Axe 2

3 The three components of the ice axe to cover are: Head Shaft Tip The ice axe has several functions, it can be used for both ascent and decent 3 and depending on the hold position it can be used for walking, digging or as a hammer. However the two different types of axe have preferable functions, the straight shaft axe is a classic design and is usually used for walking and self- arrest. Where as the curved shaft of the climbing axe is much better for climbing an icy cliff and not so good for walking. For the purposes of this assignment I will concentrate on the climbing axe because its requirements are above and beyond that of the walking axe with is also reflected in the price of axe. Climbing axes appear to be nearly double the price of a classic straight axe. Design requirements: The strength of the material is critical to its function and this needs to be accounted for in selection. The axe should be able to operate at low temperatures. Cost of materials should be considered. The components should be lightweight, so are preferable to the user when climbing. The tip of the axe needs to hold its edge throughout repeated use Page 2

4 Materials Selection Assignment - James Higson Identification of Components and their Loading The head of the Axe holds the Tip to the Shaft it needs to be strong because it transfers a lot of force from climber to ice and in reverse can be used as a hammer. The Tip of the axe is primarily for digging in to ice. It creates a hold for a climber to pull himself or herself up on. It can also be used to self arrest a slip on ice whilst walking. Modern technical axes are capable for holding a force of 2.4kN at the tip of the axe5. The shaft of the axe provides and extension to the climbers arm, so more force can be applied to smashing to ice. This being the largest part of most axes it highly contributes to the weight of the product. They generally range from 60 to 90 cm4. Page 3

5 Specification of Performance Requirements at the Component Level All components are used in operational temperatures below 0 0 C. The environment is corrosive due to water and possibly salt water, regular thermal contraction and expansion. The Head The illustration to the left shows the axe design and below is a rendered Photoshop image of the head of the axe. The head of the axe is one of the most important components because it takes the load of the climber and connects it to the tip of the axe. This means it must be strong enough to bear a load representing a person and any kit they may realistically be carrying. Because of the large forces, I will be considering the tensile and sheer strength of the component whilst at sub zero temperatures and trying to minimise cost. The Tip The tip of the axe under goes a lot of wear and force, it needs several properties to survive; It must be durable withstand the low temperatures of the environment, stiff so it doesn t buckle under force from the climbers weight, tough so the sharp edges don t allow cracks to propagate, the material must also be hard to resist indentation from the hard ice and it must also have strength to withstand compressive impact. I m going to prioritise toughness and stiffness because I think there is a large potential for crack propagation, and the head is no use if it starts to bend plastically. Page 4

6 The Shaft The shaft of the axe is under tension due to the weight of the climber. It must also be resilient to damage such as dents and crack propagation. The shaft needs to be stiff so it can transfer energy in to the ice without bending. Tensio Tension Weight of climber Page 5

7 Design translation at the Component Level The Head Comments Function TIE Being pulled apart by Climber and Tip Objective Cost and Mass Material price, Climbers overall weight Constraints Safety: tensile strength and Must not buckle or have a critical fracture (ranked in order of importance) sheer strength as this is a safety critical product Free Variables Shape, Colour Shapes can vary greatly The Tip Comments Function Beam and Column Column upon impact Objective Cost and Mass Material price, Climbers overall weight Constraints Safety: Toughness and Must not be badly become badly worn (ranked in order of importance) compressive strength Free Variables Colour Very specific shape and size for best penetration in to ice, limits free variables The Shaft Comments Function TIE Hold Climbers weight Objective Cost and Mass Material price, Climbers overall weight Constraints Safety: tensile strength and Cannot bend when impacted on the ice (ranked in order of importance) Stiffness (Youngs Modulus) Free Variables Shape, Colour, Length Length can impact on applied force Materials Indices based on the Design Translation Based on design translation the primary constraints are; Exposure to Water (fresh), Water (salt), Soils (acidic peat), Soils (alkaline clay), Tolerance to Cryogenic Temperatures. Page 6

8 The Head The Tip The Shaft Selection of the Optimum Material using CESEduPack Because the products primary limitations are all environment related. They are the same for each component. A total of 19 materials passed this selection. Page 7

9 The Head Best Material: Stainless Steel The Tip Best Material: Stainless Steel Page 8

10 The Shaft Best Material: Stainless steel Because all of my constraints are similar it has resulted in the graphs being similar. Thus the resultant materials are the same. I have chosen this as the optimum material because it is closest to the top left corner of the graph, as this is where the ideal material would appear if there were one. Discussion Limitations of the Materials Selection Process I believe the process is limited by the usability of the software, it took me several hours to become comfortable using it. However, it is clearly accurate and has a vast amount of content. The capabilities are impressive and it appears to be capable of material selection above and beyond what I have required it to do. Therefore the only other limiting factor I can think of in the selection process is the person behind the keyboard. Validity of the Materials Selected I have previously discussed why the materials I have chosen are all the same. But to expand on this point, I think the results are particularly interesting. The graphs show that stainless steel is the best material for the criteria I have used as an input. But in a close second place you can see titanium, pure and alloys. Which in fact is one of the choice materials for the best ice axes available. 6 This shows that the graphs have a degree of accuracy to them. There is also an explanation for titanium coming second, because my x- axis is scaled to cost. Page 9

11 We know titanium is very expensive so it is put higher up axis. So it isn t an appropriate material for my affordable ice axe. References iceaxe/fuseaction/products.detail/code/e /id_colour/180/group/728/level/3 3, pg, Page 10