Agricultural and Biosystems Engineers Licensure Examination (ABELE) · Philippines · Professional Regulatory Board of Agricultural and Biosystems Engineering, PRC
Original practice questions written to the published syllabus · not past papersSizing the parts of farm machines so they do not fail: shafts, keys, joints, springs, bearings, drives and overload devices.
In the exams: GATE AG Section 2 Machine Design (belts, spur gears, shear pins recur); ICAR AICE subject 39 Units 1–2; NCEES PE machinery component design
Agricultural and Biosystems Engineers Licensure Examination (ABELE)
Machine design and analysis under power and machinery: shaft, key, belt, chain, gear, bearing and spring calculations with standard formulas and non-programmable calculators.
How our questions for Agricultural and Biosystems Engineers Licensure Examination spread across the units of Machine Design. Difficulty: 13 easy, 23 medium, 6 hard.
| Belt and chain drives | 10 | |
| Springs | 6 | |
| Keys and couplings | 4 | |
| Spur gear design (Lewis and Buckingham) | 4 | |
| The design process, materials and factor of safety | 3 | |
| Shafts under combined bending and torsion | 3 | |
| Bolted joints | 3 | |
| Welded joints | 3 | |
| Overload safety devices: shear bolts and slip clutches | 3 | |
| Rolling and sliding bearings and bearing life | 2 | |
| Knuckle and cotter joints | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
A shaft is specified in AISI/SAE 1045 steel. What does the designation tell the designer?
B. It is a plain carbon steel with about 0.45 per cent carbon
In the AISI/SAE four-digit system, the first two digits (10) mean plain carbon steel and the last two give carbon content in hundredths of a per cent (45, so about 0.45 per cent). The number is not a strength, and sulphurised free-cutting grades are in the 11xx series.
Further reading: Budynas & Nisbett, Shigley's Mechanical Engineering Design
A tractor PTO delivers 15 kW at 540 rpm to an implement. What torque does the PTO shaft carry?
A. 265 N m
T = 60 P / (2 pi n) = 60 x 15000 / (2 pi x 540) = 265 N m. Dividing power by rpm directly gives 27.8, and forgetting the factor 60 (treating n as rev/s) gives 4.42 N m. 531 N m drops the 2 from 2 pi n (60 x 15000/(pi x 540)).
Further reading: Bhandari, Design of Machine Elements
A 12 mm x 12 mm square key fixes a pulley to a 48 mm shaft transmitting 400 N m. Allowable stresses for the key are 60 MPa in shear and 100 MPa in crushing. What minimum key length is required?
A. 27.8 mm
Shear: T = tau w l d/2, so l = 2T/(tau w d) = 2 x 400000/(60 x 12 x 48) = 23.1 mm. Crushing: T = sigma c (h/2) l d/2, so l = 4T/(sigma c h d) = 4 x 400000/(100 x 12 x 48) = 27.8 mm. The key must satisfy both, so l = 27.8 mm. 23.1 mm checks shear only. 13.9 mm drops one of the halves (2T/(sigma c h d)); 55.6 mm enters the 24 mm radius in place of d.
Further reading: Bhandari, Design of Machine Elements
The hitch pin of a trailed implement is a clevis-and-pin (knuckle-type) joint. In service the pin bends and wears oval. Which statement about its design is correct?
C. The pin must be checked for bending and bearing as well as double shear, and it should be secured so it cannot work out
In a clevis the pin acts as a short beam between the fork prongs, so bending often governs; bearing pressure causes the oval wear seen. Double shear is also checked. Clearance increases bending and impact, and the securing clip matters because a lost pin causes run-away implements.
Further reading: Bhandari, Design of Machine Elements
A helical spring with 10 active coils, wire diameter 6 mm and mean coil diameter 48 mm carries 500 N. Take G = 80 GPa. What is its deflection?
B. 42.7 mm
delta = 8 P D^3 N/(G d^4) = 8 x 500 x 48^3 x 10/(80000 x 6^4) = 42.7 mm. Using 12 total coils (active plus two end coils) instead of 10 active coils gives 51.2 mm; the end coils do not deflect. Using the outer coil diameter (54 mm) gives 60.8 mm, and using 4 instead of 8 in the formula halves the answer to 21.3 mm.
Further reading: Bhandari, Design of Machine Elements
Why is the spring index (D/d) of helical springs usually kept between about 4 and 12?
D. Low indices are hard to coil and have high curvature stress; high indices tend to buckle and tangle
A small index means sharply curved wire: difficult to coil and a large Wahl correction. A large index gives a floppy spring prone to buckling and tangling in handling. Stiffness varies continuously with the index, and the Wahl factor approaches 1 as the index grows.
Further reading: Budynas & Nisbett, Shigley's Mechanical Engineering Design
A spur gear has 40 teeth and a pitch circle diameter of 160 mm. What is its module, and what is the usual textbook choice of face width?
D. 4 mm; about 40 mm
m = d/z = 160/40 = 4 mm. Face width is usually taken as about 10 m (range about 9.5 m to 12.5 m), so about 40 mm. 0.25 is z/d, the inverse.
Further reading: Bhandari, Design of Machine Elements
A farmer keeps breaking shear bolts on a post-hole digger in stony ground and replaces them with high-tensile bolts. A week later the gearbox fails. What is the correct advice?
B. Use only the specified shear bolt grade and size; if bolts break often, reduce the load or fit an auto-reset slip clutch
The shear bolt is sized to fail below the gearbox's damaging torque. A stronger bolt moves the weak link to the gearbox, which is what happened. The fix is the correct bolt and, where overloads are frequent, a self-resetting device. Welding removes protection altogether.
Further reading: Srivastava et al., Engineering Principles of Agricultural Machines (ASABE)
A V-belt drive on a chaff cutter squeals and the belts glaze within weeks. The pulleys are aligned. Which cause is most likely and what is the fix?
C. The belts are slipping because of too little tension (or a worn groove); retension to the specified value and replace worn pulleys
Squeal and glazing are signs of slip, which heats and hardens the belt surface. Correct tension and sound grooves (a belt riding low in a worn groove loses the wedge action) stop it. Loose, flapping belts slip more, oil on belts is harmful, and a flat belt grips less than a V-belt.
Further reading: Bhandari, Design of Machine Elements
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