GB1588142A - Method for non-destructive testing of solid propellant rocket motors - Google Patents

Description

(54) METHOD FOR NON-DESTRUCTIVE TESTING OF SOLID PROPELLANT ROCKET MOTORS (71) We, BAYERN-CHEMIE, GmbH, a body corporate organised under the Laws of Germany of 8261 Aschau, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a method for the non-destructive testing of solid propellant rocket motors.

Faults which result in uncontrolled combustion or decomposition may occur during the manufacture of solid propellant rocket motors or when introducing the latter into a combustion chamber. Non-destructive testing methods which guarantee that faults can be clearly detected, which are suitable for as many different types of fault as possible and which function economically are desirable.

Material testing by means of x-rays formerly served as a standard method.

Routine testing by means of x-rays requires little time at low cost.-However, it has the disadvantage that it is difficult to detect certain faults such as loose parts in the combustion chamber which cause only a very thin air gap between insulation and chamber wall or insulation and propellant. Just such faults are particularly undesirable. For some time, micro-waves, infra-red radiation and ultrasonics have been used. These more recent methods do allow considerable automation but require a relatively high outlay in equipment and therefore give rise to high material costs. Furthermore, these methods are not sufficiently sensitive for detecting some types of fault.

We have sought to overcome the described disadvantages and to suggest a method which is simple to carry out, which guarantees definite results and which functions economically.

Accordingly the present invention provides a method for the non-destructive testing of a solid propellant rocket motor having air gaps or unbonding between insulation and chamber wall or between insulation and propellant which alter the heat conductivity of the outer casing, wherein liquid crystals, which change colour as a function of temperature, are applied as fault indicators to an outer surface of said chamber wall which has a light absorbing surface adapted to contrast with the colour of the liquid crystals in their mesophase, the temperature of the motor being adjusted to below the mesophase of the liquid crystals, and heating the said outer surface uniformly to the temperature of the mesophase.

A substance which forms a mesophase within a defined temperature range, representing a liquid/crystalline state, is used as an indicator. In this state, a substance which is colourless or only slightly coloured in the liquid or solid state, appears coloured and changes its colour, sensitive to the temperature change, over the entire visible range of the spectrum. The reflecting colours which occur can only be identified clearly if there is no additional reflection of the impinging light through the background; this is prevented by a light-absorbing layer. The relationship between temperature and colour is used in the testing method of the present invention. The rocket motor to be examined is provided with a suitable light-absorbing background on an outer surface and the indicator is then applied, for example by means of a spray gun.The indicator may be present as a solution, suspension or in a microencapsulated state. The motor is then regulated to a temperature below the mesophase, that is cooled normally, and then heated uniformly on the outside so that a flow of heat is produced towards the inside of the rocket motor. If the test sample is homogeneous, i.e. contains no unbonding, then the flow of heat is also uniform, regardless of location, and thus also the temperature on the outer surface of the chamber wall. If the solid propellant rocket motor contains faults, i.e. air gaps, the heat disperses differently and causes a corresponding distribution of temperature on the surface. If the surface temperature lies in the range of the mesophase of the indicator, the temperature field appears as a coloured area. The fault in the rocket motor may thus be located.

Cholesterol derivatives or mixtures thereof are preferably used as indicators. Their mesophases should generally comprise a colur changing range of from 4 to 6"C.

In a preferred embodiment of the present invention, liquid crystals having mesophases within a range of from 19 to 400C are used, preferably those whose colour change is completed between 31 and 35"C are used.

Faults which are large in terms of area may be detected particularly clearly using the method of the present invention. The costs of the method are comparable with the costs of testing with x-rays.

The following Example illustrates the invention.

EXAMPLE A controlled unbonding 30 cm in length was artificially produced between the chamber wall and the insulation of a solid propellant rocket motor. The outside of the chamber wall was then coated with black lacquer and a 25% solution of microencapsulated liquid crystals of a cholesterol derivative, whose liqud crystalline range lay between 31 and 35"C, was applied as an indicator to the lacquer coating by means of a spray gun. The rocket motor was then cooled to + 50C and subsequently heated from the outside on a heating bed with rotation to ensure uniform heating until the colour range of the indicator was reached.

The unbonding was then clearly detected as a coloured spot in the black surrounding.

This fault was not detected in a comparative experiment using x-ray testing.

WHAT WE CLAIM IS:- 1. A method for the non-destructive testing of a solid propellant rocket motor having air gaps or unbonding between insulation and chamber wall or between insulation and propellant which alter the heat conductivity of the outer casing, wherein liquid crystals, which change colour as a function of temperature, are applied as fault indicators to an outer surface of said chamber wall which has a light absorbing surface adapted to contrast with the colour of the liquid crystals in their mesophase, the temperature of the motor being adjusted to below the mesophase of the liquid crystals, and heating the said outer surface uniformly to the temperature of the mesophase.

2. A method as claimed in Claim 1, wherein the liquid crystals have a mesophase of from 19 to 400C.

3. A method as claimed in Claim 2, wherein the colour change of the liquid crystals is completed between 31 and 35"C.

4. A method as claimed in any of Claims 1 to 3, wherein the liquid crystals are cholesteriol derivatives.

5. A method as claimed in Claim 1 substantially as herein described with reference to the Example.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. of the indicator, the temperature field appears as a coloured area. The fault in the rocket motor may thus be located. Cholesterol derivatives or mixtures thereof are preferably used as indicators. Their mesophases should generally comprise a colur changing range of from 4 to 6"C. In a preferred embodiment of the present invention, liquid crystals having mesophases within a range of from 19 to 400C are used, preferably those whose colour change is completed between 31 and 35"C are used. Faults which are large in terms of area may be detected particularly clearly using the method of the present invention. The costs of the method are comparable with the costs of testing with x-rays. The following Example illustrates the invention. EXAMPLE A controlled unbonding 30 cm in length was artificially produced between the chamber wall and the insulation of a solid propellant rocket motor. The outside of the chamber wall was then coated with black lacquer and a 25% solution of microencapsulated liquid crystals of a cholesterol derivative, whose liqud crystalline range lay between 31 and 35"C, was applied as an indicator to the lacquer coating by means of a spray gun. The rocket motor was then cooled to + 50C and subsequently heated from the outside on a heating bed with rotation to ensure uniform heating until the colour range of the indicator was reached. The unbonding was then clearly detected as a coloured spot in the black surrounding. This fault was not detected in a comparative experiment using x-ray testing. WHAT WE CLAIM IS:-

1. A method for the non-destructive testing of a solid propellant rocket motor having air gaps or unbonding between insulation and chamber wall or between insulation and propellant which alter the heat conductivity of the outer casing, wherein liquid crystals, which change colour as a function of temperature, are applied as fault indicators to an outer surface of said chamber wall which has a light absorbing surface adapted to contrast with the colour of the liquid crystals in their mesophase, the temperature of the motor being adjusted to below the mesophase of the liquid crystals, and heating the said outer surface uniformly to the temperature of the mesophase.

2. A method as claimed in Claim 1, wherein the liquid crystals have a mesophase of from 19 to 400C.

3. A method as claimed in Claim 2, wherein the colour change of the liquid crystals is completed between 31 and 35"C.

4. A method as claimed in any of Claims 1 to 3, wherein the liquid crystals are cholesteriol derivatives.

5. A method as claimed in Claim 1 substantially as herein described with reference to the Example.