プラスチックねじ締結体の締付け力の緩和を予測する一方法

抄録

The purpose of this paper is to propose a method for prediction of the decreasing with time (relaxation) of initial tightening force in bolted joint with plastics screw. The viscoelastic solution to the relaxation is derived from the elastic one using the CORRESPONDENCE PRINCIPLE. The creep tests are carried out for Poly-Vinyl Chloride (PVC) as an example of viscoelastic materials to decide both the values of the stress to which the CORRESPONDENCE PRINCIPLE can be applied and the viscoelastic models. The viscoelastic solutions are obtained under the assumptions that the bolt and nuts are viscoelastic and clamped parts are rigid. The calculated results are compared with the experimental ones of relaxation for bolted joints with PVC bolt and nuts. The main conclusions are as follows: (1) The value of the stress up to which the behavior of this material can be approximated by the linear viscoelastic model is about 20 MPa at 27°C. (2) Appropriateness of the model for distortion more greatly influences the solution because the change with time of distortion is remarkable in comparison with that of dilatation. (3) Viscoelastic behavior of this material can be expressed by 5-parameter solid model in distortion and 3-parameter in dilatation. (4) The relaxation after tightening can be predicted fairly well, if the viscoelastic models of a material are determined.