The linear viscoelastic behaviour of an injection moulding grade polypropylene is studied using theoretical and computational methods. Polypropylene has a variety of engineering applications as a component. However, it commonly exhibits viscoelastic deformations. This paper analyses the creep and recovery responses of the BJ368MO polypropylene copolymer using the Burgers and generalised Maxwell models. Within the linear viscoelastic regime, an experimental creep strain at \(20\ \text{MPa}\) is used to determine the rheological constants of the models. These constants (springs and dashpots) are determined using a nonlinear least-squares curve fitting of the experimental creep. Then they are used to predict the creep and recovery responses of the polymer at three different stresses, \(10\ \text{MPa}\), \(12.5\ \text{MPa}\) and \(15\ \text{MPa}\). The experiments are made using tensile specimens designed according to the ASTM D638-14standard. The theoretical evaluations are made using the creep and recovery equations derived from their constitutive. Whereas COMSOL Multiphysics software is used during the finite element (FE) analyses. The results of the theoretical and FE calculations are verified using creep and recovery experiments. Based on the validation analyses, both viscoelastic models showed lower deviations from the experimental results when a computational approach is used. In addition, the viscoelastic models are compared by evaluating the residuals of the creep and recovery strain predictions. The theoretical analyses showed better predictions at \(12.5\ \text{MPa}\) and \(15\ \text{MPa}\) stresses when the generalised Maxwell model is used. However, the improvements are attributed to the recovery predictions. When FE is used, the Burgers model showed lower mean absolute percentage errors (MAPEs) in all creep and recovery predictions. The model has a minimum of 6.37% error at the \(10\ \text{MPa}\) stress and a maximum of 8.23% error at the \(15\ \text{MPa}\). By comparison, the generalised Maxwell model showed a minimum of 9.24% error at \(12.5\ \text{MPa}\) and a maximum of 12.8% error at \(15\ \text{MPa}\) stresses. The novelty of this paper is on predicting the creep and recovery behaviour of the polymer using the FE and theoretical approaches in the linear viscoelastic regime. The findings suggest that the FE analyses using the Burgers viscoelastic material model provide better predictions, with all calculated errors falling below 10%.

使用理论和计算方法研究了注塑级聚丙烯的线性粘弹性行为。聚丙烯作为组件具有多种工程应用。然而，它通常表现出粘弹性变形。本文使用 Burgers 和广义 Maxwell 模型分析了 BJ368MO 聚丙烯共聚物的蠕变和回复响应。在线性粘弹性范围内，\(20\ \text{MPa}\)处的实验蠕变应变用于确定模型的流变常数。这些常数（弹簧和缓冲器）是使用实验蠕变的非线性最小二乘曲线拟合确定的。然后它们用于预测聚合物在三种不同应力下的蠕变和恢复响应，\(10\ \text{MPa}\) , \(12.5\ \text{MPa}\)和\(15\ \text{MPa}\). 使用根据 ASTM D638-14 标准设计的拉伸试样进行实验。理论评估是使用从它们的本构推导出来的蠕变和恢复方程进行的。而 COMSOL Multiphysics 软件则用于有限元 (FE) 分析。理论和有限元计算的结果通过蠕变和恢复实验得到验证。根据验证分析，当使用计算方法时，两种粘弹性模型与实验结果的偏差较小。此外，通过评估蠕变和恢复应变预测的残差来比较粘弹性模型。理论分析表明在\(12.5\ \text{MPa}\)和\(15\ \text{MPa}\)处有更好的预测使用广义麦克斯韦模型时的应力。然而，这些改进归因于恢复预测。当使用 FE 时，Burgers 模型在所有蠕变和恢复预测中显示出较低的平均绝对百分比误差 (MAPE)。该模型具有在最小6.37％的误差\（10 \ \ {文本兆帕} \）应力，并在最大8.23％的误差\（15 \ \ {文本兆帕} \） 。相比之下，广义 Maxwell 模型在\(12.5\ \text{MPa}\)处的误差最小为 9.24%，在\(15\ \text{MPa}\)处的误差最大为 12.8%压力。本文的新颖之处在于在线性粘弹性状态下使用有限元和理论方法预测聚合物的蠕变和恢复行为。研究结果表明，使用 Burgers 粘弹性材料模型的有限元分析提供了更好的预测，所有计算误差均低于 10%。