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factors responsible for micro-damage of equine tendons are cross-sectional area and collagen
content
(Riemersma and Schamhardt, 1985), composition of extra-cellular matrix (Jones and Boe, 1990),
longitudinal heterogenecity (Smith et al.,1994), inter fibre differences (Becker et al,. 1994) andelevation of core temperature ( Wilson and Goodship,1994 )
The factor of safety is the measure of design of safety margin of working load
The ultimate load when expressed in terms of unit area is known as tensile strength.
Theoretical value of TS should about 0.1 E. However, the observed TS is always several times
less (Table - 2 and 3). This discrepancy is due to the presence of micro-cracks which reduces the
strength (Epifanov, 1979).
According to Guy (1976), there is initially a tiny internal void, which grows into a micro
crack in tensile strain. Further formation of a crack relieves the elastic stress. As long as the
length of the micro-crack remains below a certain value, energy is required for it to develop.
Further extension of tendon results in a reduction of its energy. Thus, a rise in temperature will
enhance the progress of micro-crack. The cyclic tensile loading of equine tendon has been shown
to result in an elevation of core temperature (Wilson and Goodship, 1994). The cyclic
overloading creates cumulative micro-damage. When the transverse length of this micro-damage
reaches a critical value (say critical length of destructive process or simply critical length of
micro-damage), there is spontaneous rupture of the material. An
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increase in tensile strength decreases in the plastic work done in initiating fracture at the tip of
flaws.
The rate of growth of micro-crack is related with a measurement known as stress
concentration factor (K). It describes the distribution of stresses at the crack tip. When the value
of K achieves a critical value, it is known as fracture toughness, there is catastrophic failure of
the material (Pascoe, 1978). The extensor tendons of fore limb, the gastrocnemius tendon and
Achilles tendon had high tensile strength. Hence, these tendons appeared to be highly susceptible
to develop flaws.
A low but repeated (continuous or intermittent) stress can cause the rupture of the tendon.
This minimum stress is known as fatigue tensile stress. Which is obtained by stress-strain (SN)
curve. Since such study was not conducted, the FTS was assumed to be minimum working load
(= 4 CSA of muscle belly) per unit CSA of tendon. The calculated number of cycles gave an
understanding of tendon failure.
specimen.
From clinical point of view, the critical length of micro-damage and the number of cycles
of fatigue failure are important. The constant (C), appeared in eq (3), is a material property (Guy,
1976). Since the value of C was not known, the value of N was expressed in multiple of C-1
(Table4).
The critical length of micro-damage indicates the maximum transverse damage, which a
tendon can sustain under tensile strain. When the tendon attains the critical length, it ruptures
under the applied stress. The higher the stress the less is the durability of the tendon.
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