Dynamic Stress Field Simulation of Surfacing Process Using ANSYS

Literature Overview

This 2010 study by Li Yilei, Bai Qinghua, and Ma Yuejin from Hebei Agricultural University, published in "Welding Technology" (焊接技术), presents a three-dimensional finite element analysis of the stress and strain field evolution during the surfacing welding process on a flat plate. Funded by the Hebei Provincial Natural Science Foundation, this research addresses the fundamental question of how residual stresses develop during surfacing and how post-weld treatments such as hammer peening can mitigate crack formation.

Core Technical Content

The study employs ANSYS finite element software with contact element technology to perform a three-dimensional real-time dynamic simulation of the surfacing process. The thermal-mechanical coupled analysis captures the transient temperature field evolution during welding, the subsequent cooling, and the resulting residual stress distribution. The key finding is that during the welding pass, the weld zone material undergoes plastic thermal compression, while after cooling, the weld region develops tensile residual stresses and the surrounding area develops compressive residual stresses.

This stress evolution pattern is fundamental to understanding surfacing weld integrity. The tensile residual stresses in the weld zone are the primary driving force for hot cracking, cold cracking, and post-weld distortion. The compressive stresses in the surrounding material partially balance the tensile stresses but create a stress concentration at the weld toe that can initiate fatigue cracks under cyclic loading.

Simulation Methodology and Key Findings

The finite element model employs a moving heat source to represent the welding arc, with a Gaussian or double-ellipsoidal distribution to accurately capture the heat input profile. The material properties are temperature-dependent, accounting for the nonlinear elastic-plastic behavior of both the base metal and the overlay material. The contact elements at the interface between the deposited layers ensure proper stress transfer between passes.

The simulation results confirm that hammer peening (锤击处理) is an effective method for reducing welding residual stresses. The plastic deformation introduced by hammering creates compressive residual stresses that partially offset the tensile stresses from welding. The simulation shows that hammer peening can reduce the peak tensile residual stress by 30–50%, significantly lowering the risk of residual stress cracking.

Stress Evolution Mechanism

The dynamic stress field evolution during surfacing can be understood through three phases:

1. Welding phase: The intense heat input causes rapid thermal expansion of the weld zone material. The surrounding cooler material constrains this expansion, creating compressive stresses in the weld zone. The material yields plastically under these compressive stresses.
2. Cooling phase: As the weld pool solidifies and cools, the weld zone contracts. However, the plastic deformation from the welding phase prevents full elastic recovery, resulting in tensile residual stresses in the weld zone. The surrounding material, which was elastically compressed during welding, springs back partially, creating compressive residual stresses.
3. Stress relaxation: Over time, if the component is exposed to elevated temperatures, stress relaxation can occur through creep mechanisms. This is particularly relevant for components in service at elevated temperatures, where residual stresses may partially self-relax.

Engineering Practice Implications

For pressure vessel and piping applications, residual stress management is a critical aspect of quality control. The simulation results provide a theoretical basis for implementing post-weld stress relief procedures. For surfacing applications on thick-walled components, the residual stress distribution can be complex, with multiple peaks and valleys depending on the number of passes, the welding sequence, and the geometry of the component.

The hammer peening technique identified in this study is a practical and economical method for residual stress reduction. It is particularly suitable for field applications where access to a stress relief furnace is limited. However, hammer peening must be performed with controlled force and pattern to avoid introducing surface damage or excessive plastic deformation. Modern practice has evolved to include shot peening and ultrasonic impact treatment as more controlled alternatives.

Study Reflections

This research demonstrates the value of finite element analysis in understanding the complex thermo-mechanical behavior of the surfacing process. The simulation provides insights that are difficult to obtain through experimental measurement alone, such as the transient stress field evolution during welding and the precise distribution of residual stresses in three dimensions. However, the accuracy of the simulation depends on the quality of the material property data and the appropriateness of the constitutive models. For engineering practice, the simulation results should be validated against experimental measurements such as X-ray diffraction or hole-drilling residual stress measurements. The study's emphasis on hammer peening as a residual stress mitigation technique is practical and directly applicable to field conditions, making it valuable for maintenance and repair operations in the oil, gas, and chemical industries.