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In most cases, some degree of embedment is inevitable. That said, short grip lengths should be avoided. For two bolted joints of identical design and installation, except the second having a longer grip length, the first joint will be more likely to loosen and fail. Since both joints have the same
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loading, the surfaces will experience the same amount of embedment. However, the relaxation in strain is less significant to the longer grip length and the loss in preload will be minimized. For this reason, bolted joints should always be designed with careful consideration for the grip length.
117:) the protruding points of the imperfect surfaces will see local stress concentrations and yield until the stress concentration is relieved. Over time, surfaces can flatten an appreciable amount in the order of thousandths of an inch.
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In bolted joints, most of the embedment occurs during torquing. Only embedment that occurs after installation can cause a loss of preload, and values of up to 0.0005 inches can be seen at each surface mate, as reported by SAE.
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in which the surfaces between mechanical members of a loaded joint embed. It can lead to failure by fatigue as described below, and is of particular concern when considering the design of critical
133:, the loss of preload due to embedment can be especially significant, causing complete loss of preload. Therefore, embedment can lead directly to loosening of a fastener joint and subsequent
129:. Flattening of a surface allows the strain of a screw to relax, which in turn correlates with a loss in tension and thus preload. In bolted joints with particularly short
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Embedment can be prevented by designing mating surfaces of a joint to have high surface
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T. Jaglinski, et al. (2007); "Study of Bolt Load Loss in Bolted
Aluminum Joints",
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If a short grip length can not be avoided, the use of conical spring washers (
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Comer, Dr. Jess. (2005); "Source of
Fatigue Failures of Threaded Fasteners",
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or disc springs) can also reduce the loss of bolt pre-load due to embedment.
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In critical fastener joints, embedment can mean loss of
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207:SAE Fatigue Design and Evaluation Committee
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145:Prevention and solutions
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178:Stress relaxation
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56:introducing
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64:June 2010
172:See also
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