MAINTAINABILITY DESIGN TECHNIQUES METRIC - AcqNotes.com

Downloaded from http://www.everyspec.com on 2011-10-29T14:56:01.DOD-HDBK-791(AM)stateside. Let us take climatic hardening as an example.Do we need to harden the entire Army inventory ofequipment to withstand an arctic climate when only 10%of the equipment is ever used there? Why not harden the10% that is supposed to endure the environment or providesupplemental environmental protection in the formof kits or shelters? Accordingly, the maintainabilityengineer—before developing a maintainability plan --should ascertain the decision of the Materiel AcquisitionReview Board, Army Materiel Command, and the ArmyTraining and Doctrine Command relative to the degree ofhardness required.Of the natural environmental factors, temperature andhumidity represent the most severe environment formaintenance in the field. Extreme cold affects the technicians’ability to handle parts, and the heavy gloves makesmall parts virtually impossible to handle or manipulate.Heavy clothing interferes with access and impairs visibility.Cold temperatures also have a deleterious effect onmany materials.Hot climates also create poor working conditions.Extremely hot temperatures, particularly if associatedwith high relative humidity, have a debilitating effect onpersonnel. Hot climates also may create difficult workingconditions. Hot, dry areas usually produce dust, whichpenetrates mechanical equipment and causes prematurewear in moving parts. Where dust accumulates, it canabsorb water; this may result in corrosion and electricalproblems. Hot, wet areas—such as the tropics causefungous growth in and on equipment.Warfare, although not an induced environmental factorin the classical sense, is an important factor. Warfareneglecting increased materiel damage—causes severemaintenance problems because of the mental stress on thetechnician; he is concerned with both his position and theurgency to return equipment to a serviceable condition asrapidly as possible. The conditions of war may also makeit difficult to obtain required repair parts and thusaggrevate the situation.Of the induced environmental factors, shock and/orvibration represent the most severe environment.Personnel performance—operator and maintenance—isadversely affected by the degree of the shock and/orvibration. These factors also can produce mechanicaldamage to materiel. Materiel experiences a variety ofdynamic mechanical loads during movement i.e., fromthe origin of manufacture to the stockpile and from thestockpile to target. Some of these loads are intrinsic to thetype of transport and handling; others are characteristicof the system itself or associated with inadvertentmishandling.10-2 ENVIRONMENTS10-2.1 NATURAL, INDUCED, ANDCOMBINEDThe components, or descriptors, of the environmentare referred to as factors. The factors (see Table 10-2 (Ref.4)) are divided into natural and induced, defined asfollows:1. Natural. Those factors primarily natural in origin.It is notable that the importance of each of these factorsmay be altered by man and. in fact, of often is whenprotection is provided.2. Induced. Those factors for which man’s activitiesconstitute the major contribution. These factors, resultingfrom man’s activity, may be controlled to any extentdeemed necessary and practical.Table 10-2 also identifies the environmental factors as toclass.The term “combined environmental factors" is used insituations to identify combinations of environrnental factorsthat frequently are observed arid that are associatedby natural coupling. In their effects on materiel, manyenvironmental factors act in conjunction or in synergism.In the conjunctive case are found examples of factors inpairs or in multiple combinations that are characteristicof geographic regions or other circumstances. Thus hightemperature and high humidity often cooccur its do hightemperature and airborne sand and dust. In the synergisticcase two or more environmental factors act together toproduce effects that are more important than the separateeffects of either constituent. An example of synergism isthe effect obtained with low temperature and vibration.With this combination of factors, rubber shock mountsthat can survive either the severe cold or the severe vibritionsreadily are destroyed by the combined action of thetwo envronmental factors. In similar fashion, the appearanceof one environmental factor may inhibit theaction of another e.g., high temperature inhibits solidprecipitants, and low temperature inhibits attack bymicrobiological organisms. Time of exposure is an importantfactor when considering the effects of combinedenvironmental factors. Table 10-3 (Ref. 2) summarizesthe qualitative relationships between pairs of environmentalfactors.For a detailed and sophisticated treatment of environmentalfactors definitions, concentrations or severityworldwide, methods of measurement, and effects on personneland materiel refer to Refs. 2, 4, 5. and 6.10-2.2 WARTIME ENVIRONMENTSWarfare—ignoring a worst case scenario of a “nuclearwinter”—will have no effect on the naturally occurringenvironmental factors presented in par. 10-2.1. Theinduced environmental factors may be increased in intensityand effects due to the employment of nuclear and orchemical munitions. Enemy and friendly fire with theattendant noise although not classical envrironrnentalfactors– must be considered in the total environrnent ofwarfare.Maintenance operations. following a nuclear or chemicalattack. will include decontamination. The guidance inthe previous chapters as to permanent labels and thedesign of doors and external fixtures so as to drain readilyand not act as liquid reservoirs will facilitate decontamination.Radiation that has been induced in materiel by anuclear explosion cannot be removed by decontamination.Accordingly, to avoid possible overexposure of personnel,speed of repair is of the essence. The guidance in10-2