Dynamic Stress and Residual Stress Analysis During Cladding of Large Frame Structures

Literature Overview and Technical Context

This study addresses the complex stress state developed during the weld overlay (cladding) process applied to large frame structures, which are commonly encountered in heavy industrial equipment such as mining machinery, construction equipment, and large-scale process plants. The cladding of large frame structures presents unique challenges compared to smaller components due to the significant geometric constraints, the large volume of material involved, and the complex interaction between the thermal field and the structural response during multi-pass welding operations.

The research focuses on the dynamic stress evolution during the cladding process, examining how residual stresses develop, redistribute, and accumulate as successive weld passes are deposited across large structural surfaces. The study employs finite element analysis (FEA) combined with experimental validation using strain gauges and X-ray diffraction residual stress measurement to provide a comprehensive understanding of the stress state in clad frame structures.

Core Technical Findings on Stress Evolution

The study reveals that the residual stress distribution in large frame structures undergoing cladding is governed by several key factors:

• Thermal gradient magnitude: The steep thermal gradient between the weld zone and the heat-affected zone generates localized tensile stresses that are subsequently redistributed as the material cools and the surrounding structure constrains the contraction.
• Sequential pass interaction: Each successive weld pass interacts with the residual stress field left by previous passes, leading to complex stress superposition and redistribution patterns.
• Structural constraint effects: The geometry of the frame structure, including the presence of stiffeners, ribs, and connected members, significantly influences the constraint level and consequently the magnitude and distribution of residual stresses.
• Deposition sequence: The order in which weld passes are laid down has a profound effect on the final residual stress state, with certain sequences capable of producing significantly lower peak stresses.

The following table presents typical residual stress values measured at various locations in a clad frame structure:

Process Optimization Strategies

The study proposes several strategies to minimize residual stresses during the cladding of large frame structures:

1. Welding sequence optimization: The analysis demonstrates that a symmetric welding sequence, progressing from the center outward or from the most constrained regions outward, produces residual stress levels 30 to 40 percent lower than a sequential edge-to-edge approach. The optimal sequence was determined through parametric FEA studies that evaluated multiple deposition patterns.
2. Interpass temperature control: Maintaining interpass temperatures between 100 and 150 degrees Celsius was found to be optimal for balancing productivity and stress control. Temperatures below 100 degrees Celsius resulted in excessive cooling rates and higher residual stresses, while temperatures above 150 degrees Celsius promoted undesirable microstructural changes in the heat-affected zone.
3. Preheating strategy: A controlled preheat of 150 to 200 degrees Celsius applied to the entire frame structure prior to cladding was shown to reduce peak residual stresses by approximately 25 percent. This preheat was applied using induced heating coils to ensure uniform temperature distribution across the large structure.
4. Post-weld stress relief: A full stress-relief annealing at 580 degrees Celsius for 4 hours per 25 mm of thickness was recommended for critical structures. This treatment reduced residual stresses to below 100 MPa in most regions, although some localized high-stress areas near sharp geometric transitions remained above 150 MPa.

Engineering Practice Implications

The findings of this study have direct implications for the fabrication of clad frame structures in industrial applications. The study demonstrates that a systematic approach to welding sequence design, combined with appropriate thermal management, can significantly reduce the residual stress levels in clad structures without compromising the overlay quality or the structural integrity of the base material.

In practical terms, the implementation of these findings requires close coordination between the welding engineering team, the structural engineering team, and the quality assurance department. The welding sequence must be designed with full knowledge of the structural constraints, and the thermal management strategy must be validated through both simulation and experimental verification before being applied to production components.

The study also highlights the importance of integrating residual stress measurement into the routine quality control program for clad structures. While residual stress measurement is not always mandated by fabrication codes, the findings demonstrate that uncontrolled residual stresses can significantly affect the fatigue life, stress corrosion cracking resistance, and dimensional stability of clad structures.

The application of these principles to specific industrial scenarios, such as the cladding of mining equipment frames exposed to abrasive wear, or the overlay of construction equipment structural members subjected to cyclic loading, requires careful adaptation of the general strategies to the specific service conditions and applicable codes.

This research contributes valuable quantitative data to the field of weld overlay stress analysis, providing engineers with a foundation for making informed decisions about welding procedure design, thermal management, and quality control for large clad structures.