Download Machine Design Assignment 9: Maximum Loads & Fasteners for Mechanical Systems - Prof. Kenn and more Assignments Machine Design in PDF only on Docsity! ME 401 – Machine Design Spring 2008, Assignment 9 Unless otherwise stated, assume n=1 and 99% reliability 1) (15 pts) A ½ - 20UNF SAE Grade 5 bolt, with rolled threads is subjected to an external tensile load which cycles from zero to Pmax. The grip length is 2.0 inches and the bolt length is 3 inches. Determine Pmax for Nfail of 100,000 load cycles. a) Use zero bolt preload (be sure to use the correct value for C with no preload) b) Use a bolt preloaded of 75% of proof c) Use a bolt preloaded of 90% of proof d) Comment on the theoretical differences resulting from the various proof loads. In reality, how does 90% preload improve fatigue over 75% preload? 2) (25 pts) For the machine shown below, two fasteners are used to attach the machine to the wall (referred to as “support fasteners”). Select the appropriate diameter for these fasteners – use SAE Grade 5. Also select an appropriate diameter for the mounting pin (also a grade 5 bolt). The load in the bar due to an eccentric mass in the spinning disk varies from 25,000 pounds compression 25,000 pounds tension. Since the compressive force will be carried by direct contact between the mounting bracket and the main structural frame (km becomes very large with compressive force), you can assume the load varies in the support fastener joint from Pmin = 0 to Pmax = 25,000lb. Dimensions for the support bar are not given. Assume factor of safety of 2 for fatigue, grip length = 1inch, 75% proof preload. You do not need to design any components other than the fasteners and pin. (PS – this is the last time you will have to see this problem – it was fun while it lasted). Main structural frame Mounting bracket Support fasteners NOT TO SCALE Rollers to prevent vertical displacement Mounting pin 3) (5 pts) An M20X1.5 Class 8.8 bolt is loaded in a shear joint as shown. Determine the maximum shear force (V) that can be applied before the bolt yields. State all assumptions. Use von Mises failure theory. 4) (10 pts) Antenna tower guy lines cannot be continuous otherwise they would interfere with the reception (current would be generated in the wires). So they are shortened and connected using ceramic insulators. The cables are looped through holes in the insulator and properly clamped. Comment on the following design for the ceramic insulator and offer an alternative. 5) (10 pts) Time for another team project – new teams, one time only teams (see table below)…and this really isn’t a project, it’s a homework problem. This problem is meant to foster ability to work on multi-disciplinary problems. Your task is as a team (2 or 3 ME’s) to meet with your EE team mate. The EE team mate’s job is to explain to you how to create a feedback block diagram (control diagram) based on the following control problem. You are to submit to me the appropriate feedback block diagram and an explanation how you created the diagram. Dr. Doughty assures me you are all qualified to understand block diagrams for control problems (unless you have not taken ME351 – let me know) but do not know how they relate to the physical/electrical systems. Now you will. You should contact the EE student via their university email – let me know if they are not responsive. Start early to allow time to find a time to meet. Each ME student is to write their own explanation – not written as a team. A negative feedback servo-system used to rotate a roof-top antenna is schematically shown in the Figure. This is a “position-sensitive” feedback system. The two potentiometers convert the angular positions, i and o, to V (shear force) V Guy line (cable) Ceramic insulator Connection (ceramic insulator) Side View Edge View Guy lines Antenna tower
