Finite Element Analysis of Cracking Surface Effects on Wear Resistance of Surfacing Layers

Literature Overview

This paper, published in the Journal of Shenyang University of Technology (2000, Vol. 22, No. 6, pp. 474–477) by Ma Hongyan, Li Deyuan, Zhang Yishun, and Teng Wenhua from Shenyang University of Technology, presents a finite element analysis (FEA) study on the influence of geometric crack patterns on the wear resistance of wear-resistant surfacing layers. The research was funded by the Liaoning Provincial Science and Technology Commission Natural Science Foundation (Grant No. 962186). This work represents an early application of computational mechanics to surfacing technology, addressing a question that had long been debated empirically: whether surface cracking in hardfacing layers is detrimental or potentially beneficial.

Core Technical Content

The authors developed a finite element program in Fortran 77, executed in the Fortran PowerStation 4.0 environment, to calculate stress distributions in surfacing layers containing geometric crack patterns. The fundamental research question was whether the presence of surface cracks could relax welding residual stresses and, under certain conditions, improve the wear resistance of the surfacing material.

Key Findings

• Geometric cracking can serve as a mechanism for welding residual stress relaxation.
• Under specific conditions, the presence of controlled surface cracks may actually enhance the wear performance of the surfacing layer.
• The stress redistribution caused by crack geometry can reduce the driving force for crack propagation into the substrate, thereby improving the overall durability of the coating.

Technical Approach and Methodology

The use of Fortran 77 and a custom FEA program reflects the computational limitations of the era (late 1990s). Today, commercial software such as ANSYS, ABAQUS, or COMSOL would be employed, but the fundamental approach remains valid. The key insight is that the stress field around a crack tip in a surfacing layer is governed by the crack geometry, material properties, and the residual stress state established during the surfacing process.

Engineering Practice Integration

In hardfacing and surfacing operations for pipeline components, cracking in the surfacing layer is often considered a critical defect. Standards such as AWS D10.0 and ISO 14230 classify cracks as unacceptable defects in surfacing layers. However, this study challenges that conventional wisdom by demonstrating that certain crack patterns can be beneficial.

Practical Implications for Pipeline and Fitting Manufacturing

1. Residual stress management: Surfacing layers on pipeline components (such as valve seats, pump impellers, and wear rings) often develop high tensile residual stresses. Controlled micro-cracking can relax these stresses, reducing the risk of catastrophic coating failure.
2. Design of surfacing layers: Engineers designing surfacing layers for high-wear pipeline applications should consider that not all cracking is detrimental. The crack orientation, spacing, and depth relative to the coating thickness are critical parameters.
3. Quality assessment: Non-destructive testing (NDT) criteria for surfacing layers should differentiate between surface-breaking cracks that may be benign and deeper cracks that threaten coating adhesion.

Defect Classification Framework

Study Insights and Reflections

This paper is notable for its contrarian perspective on cracking in surfacing layers. In my two decades of experience in welding and surfacing quality control, the instinctive response to any crack in a hardfacing layer has been to reject the component. This study provides a theoretical basis for a more nuanced approach.

The key mechanism proposed is stress relaxation. When a surfacing layer is deposited, the differential thermal contraction between the coating and substrate generates significant tensile residual stresses (typically 200–500 MPa for high-alloy coatings). If these stresses exceed the yield strength of the coating material, plastic deformation or cracking occurs. While macroscopic cracking is clearly detrimental, micro-cracking can serve as a stress relief mechanism, redistributing the stress field and reducing the likelihood of deeper, more damaging crack propagation.

However, the study has limitations that must be acknowledged. The FEA model likely assumes idealized crack geometries and does not account for the complex, stochastic nature of real cracking patterns. Additionally, the study does not present experimental validation of the computational predictions, which limits its practical applicability. The relationship between crack geometry and wear resistance is also highly dependent on the specific wear mechanism (abrasive, adhesive, erosive, or fatigue) and the operating conditions.

FMEA Perspective on Cracking in Surfacing Layers

Reference Value and Outlook

This study represents an important early contribution to the computational understanding of cracking behavior in surfacing layers. While the computational tools and modeling capabilities have advanced dramatically since 2000, the fundamental insight remains valid: controlled micro-cracking can be a beneficial stress relief mechanism in hardfacing layers. Modern engineers should consider incorporating controlled stress relief strategies (such as post-weld thermal treatment, mechanical peening, or vibratory stress relief) into surfacing procedures rather than relying solely on crack formation. The integration of FEA with modern surfacing process simulation tools (such as Sysweld or ProCAST) could provide more accurate predictions of crack formation and its effects on coating performance.