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    An Analysis of Locked-In Stresses in Automotive Cylinder Blocks

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    The stress-relaxation method is often employed to determine the locked-in stresses in complicated structures. The usual procedure is to attach electrical strain gages to the structure at positions where stresses are to be determined and then to remove the sections containing the gages by sawing or drilling. Readings of the strain gages taken before and after the removal of the sections measure the amount of relaxation resulting when the constraint of other portions of the structure is removed. From a knowledge of the modulus of elasticity of the particular material, the magnitude of the locked-in stresses in the original structure can be calculated. The method is necessarily destructive to the structure. Care must be used in the cutting and sectioning operations so as not to introduce additional stress into the structure. Residual stresses were determined by this procedure on several automotive cylinder blocks by using three types of SR-4 electrical strain gages. Where space permitted and the orientation of the stresses was not known, rectangular strain rosettes of the AR-1 type were used. These gages consist of three independent elements, two of which are at right angles to each other, and the third of which is at an angle of 45 deg. to the other two. Where the orientation of the stresses could be predicted, single-element type A-1 gages were used. Single-element type A-7 gages were used where the area of particular interest was too small to use type A-1. The surfaces upon which the gages were attached were prepared with a small hand grinder followed by sanding through No. 000 emery paper. The blocks were then heated in an oven at 120 F. to drive off surface moisture, and the gages were attached with nitrocellulose cement while the castings were still slightly above room temperature. The cement was allowed to dry in air at room temperature for 2 hr. The blocks were then placed in an oven at 120 F. for 2 hr. and then raised to 160 F. for 5 hr. to harden the cement. While the blocks were still hot, the gages were coated with high-temperature ceresin wax to prevent absorption of moisture.

    Author Information:

    Stockett, S. J.
    Research Engineer and Assistant Supervisor, Battelle Memorial Inst., Columbus, Ohio

    Lownie, H. W.
    Research Engineer and Assistant Supervisor, Battelle Memorial Inst., Columbus, Ohio

    Committee/Subcommittee: A04.21

    DOI: 10.1520/STP48063S