The load applied to a lead screw assembly is distributed amongst the engaged threads of its wearing nut in a manner that can range from highly nonuniform to nearly uniform. Nonuniform load distributions can arise when new or unworn threads are initially placed into service or, alternatively, in worn threads whereupon the operating conditions are changed from pre-existing conditions at steady-state wear. In threads wearing under constant conditions, nonuniform load distributions evolve to uniform load distributions with sufficient continued sliding as the most heavily loaded threads wear most rapidly, causing their loads to be redistributed to those threads less heavily loaded. Using a newly implemented discrete-thread numerical approach, an example lead screw with rigid nut and elastic screw body having flexible meshed thread pairs is modeled here to demonstrate the broad distribution of thread loads on a new lead screw assembly that gradually evolves toward uniformity as the coupled consideration of thread loading and wear depth approaches a steady-state of equal rates of thread wear. Thread load redistributions brought about by linear ramp changes in applied load, or temperature in the case of a nut/screw pair of dissimilar materials, are predicted at various rates of ramp between prior and future steady operating conditions. While showing the expected maintenance of uniform thread loading under slowly ramped conditions, this numerical approach was verified in cases of rapid ramps approaching step changes, for which existing closed-form analytical models provide agreement. At intermediate rates, this numerical model is complemented by newly expanded closed-form analytical models of both discrete- and continuous-thread types that describe asymptotic behavior during extended ramps.

1.
Bookwalter
,
J. C.
,
Ibidunni
,
A. O.
, and
Guenther
,
D. A.
, 1988, “
Failure Analysis of a Bed Lift Mechanism
,” ASME Paper No. 88-WA/DE-7.
2.
Kolly
,
J. M.
, and
Blanchet
,
T.
, 2005, “
Applying Research Methods in Accident Investigations
,”
NTSB Journal of Accident Investigation
,
1
, pp.
14
22
.
3.
Blanchet
,
T. A.
,
Shaffer
,
S. J.
,
Christiaen
,
A. C.
, and
Kolly
,
J. M.
, 2003, “
Grease-Lubricated Wear of Aluminum Bronze for Jackscrew Applications
,”
Wear
0043-1648,
255
, pp.
1238
1250
.
4.
Bickford
,
J. H.
, 1995,
An Introduction to the Design and Behavior of Bolted Joints
,
3rd ed.
,
Dekker
,
New York
, p.
24
.
5.
Norton
,
R. L.
, 2000,
Machine Design: An Integrated Approach
,
2nd ed.
,
Prentice-Hall
,
Englewood Cliffs, NJ
, p.
892
.
6.
Blanchet
,
T. A.
, 2006, “
Coupled Evolution of Load Distribution and Wear on Grease-Lubricated Lead Screw Threads
,”
Tribol. Trans.
1040-2004,
49
, pp.
502
512
.
7.
Sopwith
,
D. G.
, 1948, “
The Distribution of Load in Screw Threads
,”
Proc. Inst. Mech. Eng.
0020-3483,
159
, pp.
373
383
.
8.
Pick
,
R. J.
, and
Burns
,
D. J.
, 1971, “
Finite Element Analysis of Threaded End Closures of Thick-Walled Vessels
,”
Engineering Solids Under Pressure Third International Conference on High Pressure
,
Proceedings of the Institution of Mechanical Engineers
,
London
, pp.
15
25
.
9.
Miller
,
D. L.
,
Marshek
,
K. M.
, Naji, Mohammad R., 1983, “
Determination of Load Distribution in a Threaded Connection
,”
Mech. Mach. Theory
0094-114X,
18
(
6
), pp.
421
430
.
10.
Crum
,
A. S. D.
, 1988, ASME Pressure Vessels and Piping Division, PVP Publication 148, pp.
43
53
.
11.
Grewal
,
A. S. D.
, and
Sabbaghian
,
M.
, 1997, “
Load Distribution Between Threads in Threaded Connections
,”
ASME J. Pressure Vessel Technol.
0094-9930,
119
, pp.
91
95
.
12.
Murphy
,
D. J.
, 2007, “
The Coupled Evolution of Load Distribution and Wear of Lead Screw Threads
,” Ph.D. thesis, Rensselaer Polytechnic Institute, Troy, NY.
13.
Blanchet
,
T. A.
, 2007, “
Continuous-Thread Model of Load Distribution and Nut Wear in Grease-Lubricated Lead Screw Threads
,”
Tribol. Trans.
1040-2004,
50
, pp.
291
301
.
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