Abstract This paper studies the creep and damage behaviors of PMMA deep-sea manned submersible viewport windows under constant seawater pressure. First, the viscoelastic creep experiments of PMMA material specimens under four groups of tensile stresses (near 30 MPa) are performed. Second, we adopt the three-element spring/dashpot viscoelastic model to study the creep behaviors of the PMMA viewport windows without considering damage behaviors. Third, we develop a viscoelastic creep/damage coupled model to evaluate the creep behaviors of viewport windows by leveraging the Burgers viscoelastic model with four spring/dashpot elements. The main features are represented by three aspects: 1. the creep initiation, growth and acceleration stages are included, 2. the introduced damage variable into the creep model is featured by the void volume fraction, which represents the degradation of load-bearing ability of viewport windows and 3. the creep/damage coupling behaviors are reflected by the increased functional relationship between the damage variable and the equivalent strain. Fourth, the finite element algorithm using ABAQUS-UMAT (user material subroutine) is developed to implement the three-element and four-element spring/dashpot models, and the unknown viscoelastic parameters are identified by combining with the tensile creep experiments on PMMA material specimens. Finally, finite element analysis is performed to evaluate the distributions of the creep strain, displacement and damage variable of viewport windows by discussing the effects of the water depth (100–500 m and 3000 m). As an extreme case, the creep lifetime of the conical viewport window under 3000 m water depth is also evaluated from the conservative perspective.

中文翻译：

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深海载人潜水器视窗粘弹性蠕变行为有限元分析

摘要 本文研究了PMMA深海载人潜水器视口窗在恒定海水压力下的蠕变和损伤行为。首先，进行了四组拉伸应力（接近30 MPa）下PMMA材料试样的粘弹性蠕变实验。其次，我们采用三元弹簧/缓冲器粘弹性模型来研究 PMMA 视口窗口的蠕变行为，而不考虑损坏行为。第三，我们开发了一个粘弹性蠕变/损伤耦合模型，通过利用具有四个弹簧/缓冲器元素的 Burgers 粘弹性模型来评估视口窗口的蠕变行为。主要特征表现在三个方面：1.包括蠕变起始、增长和加速阶段，2.引入蠕变模型的损伤变量以空隙体积分数为特征，它代表了视口窗口承载能力的退化和 3. 蠕变/损伤耦合行为通过损​​伤变量和等效应变之间增加的函数关系来反映。第四，开发了使用ABAQUS-UMAT（用户材料子程序）的有限元算法来实现三元和四元弹簧/缓冲器模型，并结合对PMMA材料试样的拉伸蠕变实验识别未知的粘弹性参数. 最后，通过讨论水深（100-500 m和3000 m）的影响，进行有限元分析以评估视口窗口的蠕变应变、位移和损伤变量的分布。作为一个极端的情况，