Real time polarization imaging of weld pool surfaces

The search for an efficient on-line monitoring system focused on the real-time analysis of arc welding quality is an active area of research. The topography and the superficial temperature field of the weld pool can provide important information which can be used to regulate the welding parameters for depositing consistent welds. One difficulty relies on accessing this information despite the bright dazzling welding arc. In the present work, Stokes polarimetry and associated shape-from-polarization methods are applied for the analysis of the weld pool through its 810 nm-wavelength infrared emissions. The obtained information can provide a better understanding of the process, such as the usage of the topography to seek Marangoni flows direction, or to have a denser 3D map to improve numerical simulation models

Tapping Thermodynamics of the One Dimensional Ising Model

We analyse the steady state regime of a one dimensional Ising model under a tapping dynamics recently introduced by analogy with the dynamics of mechanically perturbed granular media. The idea that the steady state regime may be described by a flat measure over metastable states of fixed energy is tested by comparing various steady state time averaged quantities in extensive numerical simulations with the corresponding ensemble averages computed analytically with this flat measure. The agreement between the two averages is excellent in all the cases examined, showing that a static approach is capable of predicting certain measurable properties of the steady state regime.Comment: 11 pages, 5 figure

Glassy systems under time-dependent driving forces: application to slow granular rheology

We study the dynamics of a glassy model with infinite range interactions externally driven by an oscillatory force. We find a well-defined transition in the (Temperature-Amplitude-Frequency) phase diagram between (i) a `glassy' state characterized by the slow relaxation of one-time quantities, aging in two-time quantities and a modification of the equilibrium fluctuation-dissipation relation; and (ii) a `liquid' state with a finite relaxation time. In the glassy phase, the degrees of freedom governing the slow relaxation are thermalized to an effective temperature. Using Monte-Carlo simulations, we investigate the effect of trapping regions in phase space on the driven dynamics. We find that it alternates between periods of rapid motion and periods of trapping. These results confirm the strong analogies between the slow granular rheology and the dynamics of glasses. They also provide a theoretical underpinning to earlier attempts to present a thermodynamic description of moderately driven granular materials.Comment: Version accepted for publication - Physical Review

Coherency and Grain Size Effects on Solidification Crack Growth in Aluminum Welds

A mass-balance model has been evaluated that estimates the critical conditions for sustaining continuous crack growth in the weld mushy zone. With the aid of a strain partition model, the critical local strain rate (across the weld) has been related to the critical grain boundary deformation rate needed for crack growth. In the present work, these two models are applied to aluminum welds to investigate the theoretical effects of several metallurgical factors on solidification cracking susceptibility. Calculations quantify the improved cracking resistance associated with a smaller coherent temperature range, grain refinement, high solid fraction at coherency, and rapid development of strength

Effect of weld travel speed on solidification cracking behavior. Part 3: modeling

Solidification cracking is a weld defect common to certain susceptible alloys rendering many of them unweldable. It forms and grows continuously behind a moving weld pool within the two-phase mushy zone and involves a complex interaction between thermal, metallurgical, and mechanical factors. Research has demonstrated the ability to minimize solidification cracking occurrence by using appropriate welding parameters. Despite decade’s long efforts to investigate weld solidification cracking, there remains a lack of understanding regarding the particular effect of travel speed. While the use of the fastest welding speed is usually recommended, this rule has not always been confirmed on site. Varying welding speed has many consequences both on stress cells surrounding the weld pool, grain structure, and mushy zone extent. Experimental data and models are compiled to highlight the importance of welding speed on solidification cracking. This review is partitioned into three parts: part I focuses on the effects of welding speed on weld metal characteristics, part II reviews the data of the literature to discuss the importance of selecting properly the metrics, and part III details the different methods to model the effect of welding speed on solidification cracking occurrence

Effect of weld travel speed on solidification cracking behavior. Part 2: testing conditions and metrics

Solidification cracking is a weld defect common to certain susceptible alloys rendering many of them unweldable. It forms and grows continuously behind a moving weld pool within the two-phase mushy zone and involves a complex interaction between thermal, metallurgical, and mechanical factors. Research has demonstrated the ability to minimize solidification cracking occurrence by using appropriate welding parameters. Despite decade’s long efforts to investigate weld solidification cracking, there remains a lack of understanding regarding the particular effect of travel speed. While the use of the fastest welding speed is usually recommended, this rule has not always been confirmed on site. Varying welding speed has many consequences both on stress cells surrounding the weld pool, grain structure, and mushy zone extent. Experimental data and models are compiled to highlight the importance of welding speed on solidification cracking. This review is partitioned into three parts: part I focuses on the effects of welding speed on weld metal characteristics, part II reviews the data of the literature to discuss the importance of selecting properly the metrics, and part III details the different methods to model the effect of welding speed on solidification cracking occurrence

Effect of weld travel speed on solidification cracking behavior. Part 1: weld metal characteristics

Solidification cracking is a weld defect common to certain susceptible alloys rendering many of them unweldable. It forms and grows continuously behind a moving weld pool within the two-phase mushy zone and involves a complex interaction between thermal, metallurgical, and mechanical factors. Research has demonstrated the ability to minimize solidification cracking occurrence by using appropriate welding parameters. Despite decade’s long efforts to investigate weld solidification cracking, there remains a lack of understanding regarding the particular effect of travel speed. While the use of the fastest welding speed is usually recommended, this rule has not always been confirmed on site. Varying welding speed has many consequences both on stress cells surrounding the weld pool, grain structure, and mushy zone extent. Experimental data and models are compiled to highlight the importance of welding speed on solidification cracking. This review is partitioned into three parts: part I focuses on the effects of welding speed on weld metal characteristics, part II reviews the data of the literature to discuss the importance of selecting properly the metrics, and part III details the different methods to model the effect of welding speed on solidification cracking occurrenc

Features selection approaches for an objective control of cosmetic quality of coated surfaces

The cosmetic aspect is one of the main functions of industrial surfaces in numerous applications. Even the smallest surface defects may have a critical effect on the cosmetic tolerability of such industrial surfaces. Thus, surfaces are generally coated at the last manufacturing process stage to cover existing defects and to certify their cosmetic quality. The surface quality is however constantly controlled after coating that induces an increase of lead-time increase and production costs. This is due to a various flaw patterns and a lack of uncoated surfaces specifications. Hence, the identification of relevant surface morphological parameters underlies an objective and automatic cosmetic control performance. In fact, this relevant parameter selection allows tracking surface flaws during the coating finishing operation. This paper presents a comprehensive overview of various feature selection tools for data analysis (Neighbourhood Component Analysis (NCA), ReliefF, Sequential wrapper method, Decision tree) to extract relevant information out of physical data. A design of experiment based on scratches test on amorphous polymers to generate typical controlled defects has been performed. Then, several cosmetic defects characteristics were extracted from experimental measurements. Feature selection approaches were applied and compared to determine the most relevant parameters. The advantages and limitations of each method for data analysis have been highlighted in the case of real engineering surface quality control

Designing metallic surfaces in contact with hardening fresh concrete: A review

Concrete, a commonly used material in the construction industry, interacts with metallic surfaces such as formwork during pouring and reinforced bar during lifespan. Formworks are designed to minimize hardened concrete adherence in order to avoid wall defects after formwork removal. In opposite, reinforced bar designs aim at maximizing their adherence to concrete for optimizing the transmission of mechanical solicitations. The present review investigates the surface properties that govern bonding of freshly poured concrete onto metallic surfaces. Identifying the underlying mechanisms of adhesion highlighted the importance of substrate characteristics (roughness, composition), concrete curing and compaction), and interfacial additives (release agents, wetting). This paper addresses the basic requirements in designing a functional surface interacting with concrete and emphasizes today challenges

Weld pool surface temperature measurement from polarization state of thermal emission

This paper presents a passive polarimetry method using a division of aperture optical device in order to measure the temperature distribution at the weld pool surface. Thermal emission from a hot liquid metal was investigated at a near-infrared wavelength corresponding to a blind spectral window of a helium plasma generated during gas tungsten arc welding process. The refractive index of liquid metal and the surface radiance are deduced from the polarisation state of thermal emissions. Based upon the knowledge of both characteristics, the temperature distribution can be calculated.Conseil Régional de Bourgogn