PSI - Issue 80

Sherif Ezzeldin et al. / Procedia Structural Integrity 80 (2026) 195–202 S. Ezzeldin / Structural Integrity Procedia 00 (2023) 000–000

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flange connections are more susceptible to leakage due to uneven or insu ffi cient contact pressure during bolt tight ening, exacerbated by elastic interactions between bolts Coria et al. (2017) and the viscoelastic behavior of HDPE. Common causes of joint failure include stress relaxation Jacobsson et al. (2011), elevated temperatures Barsoum et al. (2019), misestimated bolt preload Bibel and Ezell (1992), and improper gasket design Bickford (2007). Although re-tightening can mitigate leakage, excessive torque may lead to joint failure under operational loads. To enhance joint integrity, advanced tightening strategies such as the Elastic Interaction Coe ffi cients Method (EICM) and the Tetra-Parametric Assembly Method (TAM) have been developed. TAM, introduced by Coria et al. Coria et al. (2017), simplifies the analysis by considering only four load cases, enabling e ffi cient single- or two-pass tightening sequences Coria et al. (2019). While these methods are well-validated for metallic joints, applying them to hybrid HDPE–steel flange connections introduces challenges due to the large sti ff ness mismatch and nonlinear viscoelastic-plastic behav ior of HDPE. Recent numerical studies Ezzeldin et al. (2025) have demonstrated that TAM can be e ff ectively adapted for such hybrid assemblies. This study extends that work by evaluating the long-term sealing performance of HDPE-to-steel flanged connec tions under combined thermal and mechanical loading. Unlike previous elastic-based analyses, this research incor porates time and temperature-dependent material behavior to simulate real-world conditions over extended periods. Using 3D finite element modeling and viscoelastic material models, the study builds on TAM-derived preloads to as sess both initial sealing and long-term tightness, o ff ering practical insights for maintaining joint integrity throughout service life. The Elastic Interaction Coe ffi cients Method (EICM) models bolt interactions in a joint to determine the initial loads required for uniform contact pressure. The relationship between initial and final bolt loads is defined by Eq. (1), with interactions derived from finite element analysis or experimental load measurements during sequential tight ening. It uses a square matrix [ A ], with dimensions equal to the number of bolts, where diagonal elements represent self-interaction of each bolt, and o ff -diagonal elements describe the influence of one bolt on another due to elastic deformation. EICM has been widely validated for metallic joints Coria et al. (2017), Bibel and Ezell (1992). 1.1. Elastic Interaction Coe ffi cients Method

{ F f } = [ A ] { F i }

(1)

1.2. Tetra Parametric Assembly Method

The Tetra-Parametric Assembly Method (TAM) Coria et al. (2017), Coria et al. (2019), an extension of EICM, simplifies the analysis of bolted joint interactions during tightening. Like EICM, TAM uses a sti ff ness matrix to relate applied bolt torque to resulting clamping forces, but reduces the full elastic interaction matrix [ A ] to four key parame ters: α,β,γ, and δ . These represent the influence of bolt interactions under four distinct loading scenarios. The method assumes that tightening one bolt primarily a ff ects only adjacent bolts—those one or two positions away—allowing the neglect of distant interactions. This significantly reduces computational e ff ort without simulating the entire tightening sequence. TAM parameters can be derived via FEA or experiments. While the matrix structure remains consistent across tightening patterns, its coe ffi cient arrangement varies based on the sequence. The procedure to obtain the TAM coe ffi cients is detailed in Table 1. Eq. (2) demonstrates this mapping for an 8-bolt configuration using a criss-cross (star) pattern.