GMW3137

Description / Abstract: Introduction

Note: Nothing in this standard supercedes applicable laws and regulations.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence.

Purpose. This procedure describes the continuous measurement of stress (distribution) between the static gasket, O-ring or seal and joint surfaces using an electronic sensor film (e.g., Tekscan, FlexiForce Division). Stress measurement is a change in the sensor’s electrical resistance as a function of load. The sensor’s multiple contact points create a grid or stress distribution response. The changing (dynamic) force on a gasket given the tightening method, temperature, and sensor capability is observed (visual display) and measured.

Applicability.

Differences from GMW3152. GMW3152 (Static Sealing Pressure Measurement for Powertrain Sealing Systems) uses pressure sensitive micro-encapsulated color forming film, measuring only the maximum pressure under specified assembly conditions. This procedure is used where a more detailed level of surface contact pressure analysis is needed.

Test results may be used to verify finite element analysis stress results.

Useful for comparing component elements, e.g., various torque sequences or effect of torque on flange distortion and contact seal force.

Limitations. For joints larger than the sensor, use multiple sensors (butt joint) and combine the pressure maps to provide a total load distribution.

Consult the sensor manufacturer on calibration, accuracy, resolution and drift with used sensors. Replace if measurement problems cannot be resolved.

Results are rate dependent. Data output is screen displayed in Two Dimensional (2D) or Three Dimensional (3D). Skill in print configuration and code for data printout is required.

Measurements during thermal cycling are not practical due to calibration shifts in sensor and impact of joint motion on sensor durability. The sensor film may also become a leak path if used during GMW3155.

Load Measurement Range. Tekscan sensors have a 4.5 N to 445 N range (1 lbF to 100 lbF).

Temperature and Humidity Range. Unless otherwise specified, load measurements are at 0% to 100% relative humidity and 23 °C ± 3 °C. High temperature sensors are now available for measurements up to 150 °C. Standard sensor measurement range is -9 °C to 50 °C under isothermal conditions.

Note: Sensors are not temperature compensating. Calibrate at the measured temperature.

Remarks. This procedure is mandatory on production drawings requiring its use, for any material, design or process change made to all production static powertrain sealing systems. The minimum required sealing pressure is specified by the GM Powertrain release engineer responsible for the tested part or in the appropriate Statement of Requirements, Bill of Design or Bill of Material level.

The values stated in either the International System of Units or English units are to be regarded separately as standard. Combining values from the two systems may result in nonconformance with the test procedure