Yes - a joint will experience "slow damage", of course. But the differences are that 1) the body can repair some of the damage 2) Muscles etc surrounding the joint will grow stronger/more efficient over time, lessening the impact to some extent (note - I'm not a biologist, I'm just applying common sense). Clearly, age (affecting rate of cell replication and therefore repair) and general health of the person will impact how well the body can compensate.

My guess is the the wear and tear on a mechanical system would be generally linear over time, until a point where the damage was significant enough to change the failure mode (e.g. exceeding an elastic limit, or reaching a concentration of stress fractures which would cause complete mechanical failure)

A joint in a human body would potentially show an initially steep rate of damage, followed by more of a plateau region as the cell renewal (joint repair) and muscle strengthening begin to compensate for the potential damage.

I'm sure there will be literature available to compare with - have a look at studies on the wear and tear on artificial hip joints where they compare with a control group with no hip replacements

Thanks a lot for the well articulated reply. Yes, offcourse the human body gets nourished by our food intake. But if the fatigue load is sure to cause slow damage, then is cycling everyday considered good or bad, because its said that exercising is good for the body.

"Exercise is good for the body" is a catch-all holistic phrase, you can't think of that with respect to mechanical function of one joint in isolation. The NET benefits of exercise are - of course - good for the body.  For example - cycling every day for an entire lifetime up and down a mountain, might, very gradually, do some damage to a joint, but it will strengthen the cardiovascular system and leg muscles enormously - and the major health problems that people generally need to protect against are heart attack/stroke etc (the negative health impacts of too little exercise/too many calories etc)

Cycling is generally a low impact sport, especially if compared to running/athletics etc and so would impact joints much less severely - therefore the overall benefits of the exercise would far outweigh any (potential) joint damage. Our joints are designed with in-built cushioning so that they do perform well over repeated cycles (evolution! - we're a species who were designed for running over long distances!) and are designed to last a lifetime. Things like arthritis obviously disrupt that, but the core design is good. It's obviously different if you're talking about an athlete cycling in something like the Tour de France, where the joints are being exposed to much greater intensity.

Anyone taking up a new activity for the first time should increase the amount they do slowly, therefore in your example, the person shouldn't try to cycle all the way up the mountain on day 1! That has the potential to cause joint damage as the muscles surrounding their knee/ankle wouldn't be strong enough. Our body is really good at telling us if we're doing too much too quickly - things hurt for a reason :-) - we have a good inbuilt system to help warn us - but then as our muscles and cardiovascular system strengthen we can do more.

I understand your question - but if it's for a research project you'll have to define your terms of reference much more closely to make your results meaningful. It will be difficult to compare the performance of a real human knee joint to a mechanical knee to test the statement "exercise is good for the body" :-)

This was explained to us years ago:

Wolff's law, developed by the German anatomist and surgeon Julius Wolff (1836–1902) in the 19th century, states that bone in a healthy person or animal will adapt to the loads under which it is placed. If loading on a particular bone increases, the bone will remodel itself over time to become stronger to resist that sort of loading.The internal architecture of the trabeculae undergoes adaptive changes, followed by secondary changes to the external cortical portion of the bone, perhaps becoming thicker as a result. The inverse is true as well: if the loading on a bone decreases, the bone will become less dense and weaker due to the lack of the stimulus required for continued remodeling. This reduction in bone density (osteopenia) is known as stress shielding and can occur as a result of a hip replacement (or other prosthesis). The normal stress on a bone is shielded from that bone by being placed on a prosthetic implant.

Only contribution I feel adding to the exhaustive answers that were already given is related to "tribology" of the bone where it can be considered as having mechanical properties like different materials ( e.g. metal). Thus, fractures may occurr when the material is exposed to stresses that exceed its resistance, well over elastic and plastic deformation. In addition, AFA plastic deformation is concerned we should also take into account fatigue of the material, which speaking of bone corresponds to low intensity repeated stresses (e.g. marching) that may lead to stress fractures. Those considerations do not usually apply to joints because of the presence of cartilage, etc. 

Surely the answer is the same as for almost every aspect of life..  moderate exercise/eating/drinking/sex/working/reading etc etc is good for you, life-enhancing; excessive exercise/eating/drinking/sex/working reading etc.. leads to trouble..

To build off Brian Carpenter's response, bouts of cyclic loading cause microtrauma accumulation over time (Davis, 1867; Wolff, 1892). When microtrauma from a given bout of loading is limited, and biological structures are allowed adequate time for repair, they can positively remodel, becoming stronger and less susceptible to injury (e.g., Burr et al., 2002; Shepherd & Screen, 2013). In contrast, structures become vulnerable to overuse injury when successive bouts of loading occur before microtrauma can be repaired. Such microtrauma accumulation overwhelms repair processes, elicits negative remodelling, and increases injury risk (Rolf, 1995; Frost, 1998; Hreljac, 2004; Edwards et al., 2009; 2010).

Here are some papers on the subject that I find interesting:

https://www.researchgate.net/publication/256665001_Why_Don%27t_Most_Runners_Get_Knee_Osteoarthritis_A_Case_for_Per-Unit-Distance_Loads

https://www.researchgate.net/publication/41122367_Effects_of_running_speed_on_a_probabilistic_stress_fracture_model

https://www.researchgate.net/publication/38091426_Effects_of_Stride_Length_and_Running_Mileage_on_a_Probabilistic_Stress_Fracture_Model

Article Why Don't Most Runners Get Knee Osteoarthritis? A Case for P...

Article Effects of running speed on a probabilistic stress fracture model

Article Effects of Stride Length and Running Mileage on a Probabilis...

I am thankful to the exhaustive answers I received. Eventhough my field of research is impact on composite materials, this question was a result of curiosity or personal experience with biking. While reading the answers, its interesting to see how discussions travel through material science and human body anatomy. So to conclude, human body is  a much technologically advanced material compared to the manufactured materials, and still we are yet to manufacture materials which can behave like a human body.