机械机器和机器零件的设计外文文献翻译（中文文-字数8750字）

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Design of machine and machine elements

Machine design

Machine design is the art of planning or devising new or improved machines to

accomplish specific purposes. In general, a machine will consist of a combination of several

different mechanical elements properly designed and arranged to work together, as a whole.

During the initial planning of a machine, fundamental decisions must be made concerning

loading, type of kinematic elements to be used, and correct utilization of the properties of

engineering materials. Economic considerations are usually of prime importance when the

design of new machinery is undertaken. In general, the lowest over-all costs are designed.

Consideration should be given not only to the cost of design, manufacture the necessary

safety features and be of pleasing external appearance. The objective is to produce a

machine which is not only sufficiently rugged to function properly for a reasonable life, but

is at the same time cheap enough to be economically feasible.

The engineer in charge of the design of a machine should not only have adequate technical

training, but must be a man of sound judgment and wide experience, qualities which are

usually acquired only after considerable time has been spent in actual professional work.

Design of machine elements

The principles of design are, of course, universal. The same theory or equations may be

applied to a very small part, as in an instrument, or, to a larger but similar part used in a

piece of heavy equipment. In no ease, however, should mathematical calculations be looked

upon as absolute and final. They are all subject to the accuracy of the various assumptions,

which must necessarily be made in engineering work. Sometimes only a portion of the total

number of parts in a machine are designed on the basis of analytic calculations. The form

and size of the remaining parts are designed on the basis of analytic calculations. On the

other hand, if the machine is very expensive, or if weight is a factor, as in airplanes, design

computations may then be made for almost all the parts.

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The purpose of the design calculations is, of course, to attempt to predict the stress or

deformation in the part in order that it may sagely carry the loads, which will be imposed on

it, and that it may last for the expected life of the machine. All calculations are, of course,

dependent on the physical properties of the construction materials as determined by

laboratory tests. A rational method of design attempts to take the results of relatively simple

and fundamental tests such as tension, compression, torsion, and fatigue and apply them to

all the complicated and involved situations encountered in present-day machinery.

In addition, it has been amply proved that such details as surface condition, fillets, notches,

manufacturing tolerances, and heat treatment have a market effect on the strength and useful

life of a machine part. The design and drafting departments must specify completely all such

particulars, must specify completely all such particulars, and thus exercise the necessary

close control over the finished product.

As mentioned above, machine design is a vast field of engineering technology. As such, it

begins with the conception of an idea and follows through the various phases of design

analysis, manufacturing, marketing and consumerism. The following is a list of the major

areas of consideration in the general field of machine design:

① Initial design conception;

② Strength analysis;

③ Materials selection;

④ Appearance;

⑤ Manufacturing;

⑥ Safety;

⑦ Environment effects;

⑨ Reliability and life;

Strength is a measure of the ability to resist, without fails, forces which cause stresses and

strains. The forces may be;

① Gradually applied;

② Suddenly applied;

③ Applied under impact;

④ Applied with continuous direction reversals;

⑤ Applied at low or elevated temperatures.

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If a critical part of a machine fails, the whole machine must be shut down until a repair is

made. Thus, when designing a new machine, it is extremely important that critical parts be

made strong enough to prevent failure. The designer should determine as precisely as

possible the nature, magnitude, direction and point of application of all forces. Machine

design is mot, however, an exact science and it is, therefore, rarely possible to determine

exactly all the applied forces. In addition, different samples of a specified material will

exhibit somewhat different abilities to resist loads, temperatures and other environment

conditions. In spite of this, design calculations based on appropriate assumptions are

invaluable in the proper design of machine.

Moreover, it is absolutely essential that a design engineer knows how and why parts fail so

that reliable machines which require minimum maintenance can be designed. Sometimes, a

failure can be serious, such as when a tire blows out on an automobile traveling at high

speeds. On the other hand, a failure may be no more than a nuisance. An example is the

loosening of the radiator hose in the automobile cooling system. The consequence of this

latter failure is usually the loss of some radiator coolant, a condition which is readily

detected and corrected.

The type of load a part absorbs is just as significant as the magnitude. Generally speaking,

dynamic loads with direction reversals cause greater difficulties than static loads and,

therefore, fatigue strength must be considered. Another concern is whether the material is

ductile or brittle. For example, brittle materials are considered to be unacceptable where

fatigue is involved.

In general, the design engineer must consider all possible modes of failure, which include

the following:

① Stress;

② Deformation;

③ Wear;

④ Corrosion;

⑤ Vibration;

⑥ Environmental damage;

⑦ Loosening of fastening devices.

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附录附录1DesignofmachineandmachineelementsMachinedesignMachinedesignistheartofplanningordevisingneworimprovedmachinestoaccomplishspecificpurposes.Ingeneral,amachinewillconsistofacombinationofseveraldifferentmechanicalelementsproperlydesignedandarrangedtoworktogether,asawhole.Duringtheinitialplanningofam...

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