Conclusion

• For durability of materials , agents do not act uniformaly i.e. individual agents have differing affects on different materials . For example , plastics are not attacked by corrosion , fungi , insects but are susceptible to damage by ultra-violet radiation .
• Besides, the extent of any damage is likely to vary according to the nature of the attack  . For damage by corrosion , for instance  , the duration of the attack is the critical factor ; whereas in the case the thermal movement , the intensity of the agent is the dominant consideration .