MIL-STD-202H.pdf - 第45页

MI L - S TD - 202 - 107 M E TH O D 1 0 7 T HE R M A L S HO CK 1. SCOPE 1. 1 P urpose . T his test i s c on duc t ed f or t he pur p os e of d et e r m i ni ng t he r e s i s t an c e of a pa rt to ex posures at extr emes…

MIL-STD-202-107

CONTENTS

PARAGRAPH PAGE

FOREWORD…………………………………………………………. ii

1. SCOPE 1

1.1 Purpose………………………………………….……..…………. 1

2. APPLICABLE DOCUMENTS 1

3. DEFINTIONS 1

4. GENERAL REQUIREMENTS 1

4.1 Apparatus………………………………………….…...…………. 1

4.1.1 Environmental chambers........................................................ 1

4.1.2 Liquid baths ………………………………...………...…………. 1

4.2. Procedure………………………………………..……..…………. 2

4.2.1 Environmental chambers.….……………………………………. 2

4.2.2 Liquid baths.…………………………………………..…………. 2

4.3 Measurements……………………………………………………. 2

5. DETAILED REQUIREMENTS 2

5.1 Summary……………………………..…………..………………. 2

6. NOTES 5

6.1 Supersession data………………………………………………. 5

6.2 Cancelled Method……………………………..…………………. 5

TABLES PAGE

I Thermal shock test conditions (air)………………….…………….……… 3

II Exposure time in air at temperature extremes………………………...... 3

III Thermal shock conditions (liquid)………………………………………… 4

IV Suggested thermal fluids………………………………………………….. 4

V Exposure time in liquid at temperature extremes…...................……… 5

iii

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MIL-STD-202-107

METHOD 107

THERMAL SHOCK

1. SCOPE

1.1 Purpose. This test is conducted for the purpose of determining the resistance of a part to exposures at

extremes of high and low temperatures, and to the shock of alternate exposures to these extremes, such as would be

experienced when equipment or parts are transferred to and from heated shelters in arctic areas. These conditions

may also be encountered in equipment operated noncontinuously in low-temperature areas or during transportation.

Although it is preferred that the specimen reach thermal stability during the exposure specified, in the interest of

saving time, parts may be tested at the minimum exposure durations specified, which will not insure thermal stability

but only an approach thereto. Permanent changes in operating characteristics and physical damage produced during

thermal shock result principally from variations in dimensions and other physical properties. Effects of thermal shock

include cracking and delamination of finishes, cracking and crazing of embedding and encapsulating compounds,

opening of thermal seals and case seams, leakage of filling materials, rupturing, or cracking of hermetic seals and

vacuum glass to metal seals, and changes in electrical characteristics due to mechanical displacement or rupture of

conductors or of insulating materials.

2. APPLICABLE DOCUMENTS

This section not applicable to this standard.

3. DEFINTIONS

This section not applicable to this standard.

4. GENERAL REQUIREMENTS

4.1 Apparatus. Suitable temperature controlled systems shall be used to meet the temperature requirements and

test conditions specified in table I or table III. The liquid method is more severe and may damage some components

that might not be degraded by the air method. It is not intended for use on nonhermetically sealed components.

4.1.1 Environmental chambers. A system of sufficient thermal capacity shall be used to change ambient chamber

conditions to meet test requirements and to reach specified temperature conditions of steps 1 and 3 of table I. The

supply air temperature of the chambers shall reach the specified temperature within a recovery time of 5 minutes

after the specimens have been transferred to the appropriate chamber.

4.1.2 Liquid baths. Suitable temperature controlled baths containing liquids (see table IV) shall be chosen to

maintain the specified test conditions (see table III) within the indicated tolerances. A liquid media shall not be used

without prior approval of the qualifying activity.

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MIL-STD-202-107

4.2. PROCEDURE.

4.2.1 Environmental chambers. Specimens shall be placed so that there is substantially no obstruction to the flow

of air across and around the specimen. When special mounting is required, it shall be specified. The specimen shall

be subjected to the specified test condition of table I. The first five cycles shall be run continuously. After five cycles,

the test may be interrupted after the completion of any full cycle, and the specimens allowed to return to room

ambient temperature before testing is resumed. One cycle consists of steps 1 through 4 of the applicable test

condition. Specimens shall not be subjected to forced circulating air while being transferred from one chamber to

another. Whether single or multiple chambers are used, the effective total transfer time from the specified low

temperature to the specified high temperature, or the reverse, shall not exceed 5 minutes. Direct heat conduction to

the specimen should be minimized. In the case of multiple chambers, the transfer time shall be defined as the time

between withdrawal from the low temperature chamber and introduction into the high temperature chamber or the

reverse.

NOTE: In single compartment chambers, in which the temperature extremes of steps 1 and 3 are achieved without

physical movement of the specimens, steps 2 and 4 are not applicable.

4.2.2 Liquid baths. Specimens shall be immersed in a suitable liquid that shall be approved by the qualifying

activity (see table IV), at the temperature in step 1 of the specified test condition (see table III) for the time specified in

table V. Immediately upon the conclusion of step 1, the device shall be transferred to a suitable liquid at the

temperature specified in step 2 of the specified test condition. The device shall remain at the high temperature for the

time specified in table V. These two steps, step 1 and 2, constitute one cycle of the applicable test condition. Repeat

the required number of cycles without interruption as specified in table III. Transfer time from low to high temperature

and from high to low temperature shall be less than 10 seconds.

4.3 Measurements. Specified measurements shall be made prior to the first cycle and upon completion of the final

cycle, except that failures shall be based on measurements made after the specimen has stabilized at room

temperature following the final cycle.

5. DETAILED REQUIREMENTS

5.1. Summary. The following details are to be specified in the individual specification:

a. Recovery time if other than 5 minutes (see 4.1.1).

b. Special mounting, if applicable (see 4.2).

c. Type test (air or liquid) and test condition (see 4.2).

d. Transfer time if other than specified in 4.2.1 or 4.2.2.

e. Measurements before and after cycling (see 4.3).

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