Abstract
In car body, many types of high strength steel sheets are used. Because the strength of many body parts are mainly dependent on the strength of spot welded joints, estimation of joint strength becomes important. JIS Z 3136 prescribes tensile shear test method as the representative test for spot welded joint, and tensile shear strength (TSS) has been regarded the most important property for thin sheet structure. Up to this time, many experimental formula are known to estimate TSS from factors of tensile strength of base metal, sheet thickness and nugget diameter. However, in those estimation the applicable range was limited, and there was no way to break the limit. The reason was seemed that there was a few consideration to roles or meanings of above three factors on TSS.Then, in the present study the new estimation are tried to lead by a simple fracture model which has practically satisfactory precision to low carbon steel sheets used for car body, and which has a appreciate easy form related above factors. The estimation formula is as the following. TSS=2.05t·TS(1+0.0059EL) (ND+2.09).TSS is in N, t is thickness in mm, TS and EL are strength in N/mm2 and elongation in % of base material respectively and ND is nugget diameter in mm. The value EL was the factor concerned with the width of stress distribution. Fracture was occurred outside the hardened region, then TSS was not in proportion to ND simply.
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