Polymer Scratch Research Articles

Effect of physical aging on scratch behavior of polycarbonate

AbstractPhysical aging refers to relaxation of the polymer glassy state toward the amorphous state and this phenomenon affects their physical‐mechanical properties. This work investigates the effect of physical aging on polymer scratch behavior and visibility. It was shown that mechanical properties were significantly modified over the aging time, especially the yield stress, in turn affecting polymer scratch behavior. As a matter of fact, the critical load for the onset of scratch visibility was shown to increase with the aging, thus improving sensitivity of polymer to scratches. Such behavior was strictly related to the yield stress increase with the aging time. The usefulness of the present work is highlighted, and some future perspectives are discussed.

Effect of color on scratch and mar visibility of polymers

AbstractPolymer scratch mechanics has been widely studied. However, the physics behind scratch visibility is still not well understood. Scratch deformation mechanisms certainly affect visibility but also other material properties, such as roughness, color, or gloss. This work relates to methods to quantitatively evaluate the effect of sample color on polymer scratch and mar induced visibility, aiming at linking scratch behavior with the underlying physics. A custom‐built black box was utilized for the analysis of samples possessing different colors and surface finishing. Automatic image analysis was performed through a commercial software to quantify the onset of visibility in terms of a critical load above which the scratch becomes visible. Trained surveyors visually quantified said critical load. White color was shown to delay the onset of visibility by reducing the contrast between the damaged and undamaged area. For instance, the critical load for the onset of visibility for a white polycarbonate copolymer was nearly twice the value reported for its black variant. Consistent results were obtained for all tested samples. Similar findings were reported for the mar phenomenon, highlighting how white color can also mask a different type of damage. The usefulness of the present work and some future perspectives are discussed.

Influence of sliding velocity on microscratch response of carbohydrate polymers by Berkovich indenter

Microscratch tests were carried out on polyamide (PA) and polypropylene (PP) by Berkovich indenter to study influence of sliding velocity on microscratch response of carbohydrate polymers. Both penetration depth and residual depth decrease nonlinearly with the increase of sliding velocity. Elastic deformation is dominant in the total deformation during scratching of polymers. Both residual and contact scratch widths decrease nonlinearly with sliding velocity. The elastic recovery rate increases with sliding velocity. Both scratch hardness and lateral hardness increase nonlinearly with sliding velocity. Scratch hardness also increases nonlinearly with the increase of strain rate due to strain rate hardening effect. Scratch friction coefficient of PA decreases with increasing sliding velocities, and can be regarded to be constant under large sliding velocities. Nevertheless, scratch friction coefficient of PP increases with sliding velocity. Residual scratch grooves, scratch friction coefficient, and lateral force under different sliding velocities can be used to reveal the different friction mechanisms of PA and PP.

Micromechanical performance of high-density polyethylene: Experimental and modeling approaches for HDPE and its alumina-nanocomposites

The scratch resistance of polymers is important for numerous applications, as scratching can lead to degradation of surface properties and also represents an elementary process in abrasive wear. However, scratching of polymers is a complex process involving several modes of deformation, and theoretical understanding of it is incomplete. Numerical modeling is a potentially useful means towards a clearer picture of the scratching process, but the central role of tip-substrate contact and highly localized large deformations makes finite element analysis (FEA) challenging. Here, we take further the numerical approach by investigating a highly ductile semi-crystalline polymer by FEA and taking the inherent rate dependency of polymers into account by using an elasto-viscoplastic material model. Two γ-Al2O3 and f-Al2O3 HDPE nanocomposites, which have shown themselves to be suitable for tribological applications, are studied. We discussed the effect of nanofillers on the scratch behavior and highlight the significance of recovery properties, which still pose a challenge to numerical modeling.

Mechanism of temperature rise due to crazing evolution during PMMA scratch

Dramatic temperature rise has been observed at the surface facture area during the scratch of brittle poly(methyl methacrylate) (PMMA). However, the strain energy accompanied with the macroscopic linear elastic fracture is inadequate to explain the significant temperature change. To describe this phenomenon, the crazing related energy dissipation mechanism considering the evolution of microscopic crazing is proposed in this paper. The algorithm to calculate the crazing-induced temperature rise is presented. After validated by the experiment and finite element (FE) simulation for the tension of a thin plate with a circular hole, the proposed approach is utilized to investigate the scratch-inducedtemperature rise with the combination of FE simulation. The frictional heating and macroscopic plastic deformation make their contribution for the temperature rise at relative small scratch load. The energy dissipated by the crazing process plays a dominating role for the scratch-induced fracture. Those findings provide meaningful insight for understanding the mechanism of temperature rise during polymer scratch.

In-situ observation of temperature rise during scratch testing of poly (methylmethacrylate) and polycarbonate

In this work, an in-situ observation of temperature rise during the scratch test was performed for both brittle and ductile polymeric materials, i.e., poly (methylmethacrylate) (PMMA) and polycarbonate (PC). Significant temperature rise of the scratched polymer substrate has been observed for both PMMA and PC, though their scratch damage modes are quite different. Frictional heating is the main reason of the temperature rise under the low scratch normal load, while the plastic deformation and severe damage are responsible for the temperature rise under high load level. Since the DSC results clearly show that the microstructures of PMMA and PC are altered, the temperature rise during the scratch process has to be considered for the further investigation of polymer scratch.

Study of Material Parameters’ Effect on Polymer Scratch Using SOM Method

Due to its inherited complexity, the polymer material parameters’ effect on the scratch resistance is difficult to detect. Using the scratch experimental results of a set of polypropylene (PP), the Self-Organizing Map (SOM) method, an artificial neural network algorithm, was adopted to study the effect of various material parameters on polymer scratch. Especially suitable for the analysis of high-dimensional data with nonlinear statistical relationships, SOM method helps to find out the influence of different material parameters on scratch behavior. This information can be used to estimate the possible performance of polymeric materials to certain extent without extra scratch experimental work. It also helps researchers to decide which group of properties should be paid more attention when studying the coupling effect of material parameters on polymer scratch resistance.

Study of Material Parameters’ Effect on Polymer Scratch Using SOM Method

Due to its inherited complexity, the polymer material parameters’ effect on the scratch resistance is difficult to detect. Using the scratch experimental results of a set of polypropylene (PP), the Self-Organizing Map (SOM) method, an artificial neural network algorithm, was adopted to study the effect of various material parameters on polymer scratch. Especially suitable for the analysis of high-dimensional data with nonlinear statistical relationships, SOM method helps to find out the influence of different material parameters on scratch behavior. This information can be used to estimate the possible performance of polymeric materials to certain extent without extra scratch experimental work. It also helps researchers to decide which group of properties should be paid more attention when studying the coupling effect of material parameters on polymer scratch resistance.

Effects of acrylonitrile content and molecular weight on the scratch behavior of styrene‐acrylonitrile random copolymers

AbstractFundamental understanding of the scratch behavior of styrene‐acrylonitrile (SAN) random copolymers with variation in acrylonitrile (AN) content and molecular weight (MW) is pursued using the methodology outlined in ASTM D7027‐05/ISO 19252:08. Two sets of SAN model systems are employed: One that varies the AN content with similar MW and another that varies the MW at the same AN content. Key scratch damage mechanisms (scratch groove formation, periodic micro‐cracking, and plowing) are identified and correlated with the compressive and tensile properties of the SAN systems. Scratch visibility is analyzed through the use of a commercial software package. A fundamental structure–property relationship of SAN scratch behavior is proposed by the fact that increasing the AN content or the MW can have a positive effect on increasing the scratch resistance of SAN as it improves its tensile strength and ductility. The implication of material properties and their effect on polymer scratch behavior is discussed. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Quantitative evaluation of scratch visibility resistance of polymers

Susceptibility of polymer surfaces to acute visibility upon scratching has presented a serious challenge to the polymer industry for quite some time. The ability to design polymers with good scratch visibility resistance requires extensive knowledge about scratch deformation mechanisms and their propensity for light scattering. After examining the physical nature of human vision and surface optical characteristics, a new methodology is developed to quantitatively determine the onset of scratch visibility of polymers via an inexpensive desktop scanner. Taking into account the sample background color, texture, gloss and feature size, the proposed methodology can consistently and reliably determine polymer scratch visibility resistance regardless of the sample surface characteristics. Good correlation is found between this method and actual human perception. Quantitative analysis of the scratched surface is carried out with scanning laser profiling confocal microscopy and strong correlations among scratch visibility, observation angle and various scratch damage features such as roughness and scratch grooves are established. The proposed approach will greatly assist the development of scratch-resistant polymeric materials where surface aesthetics is of primary concern.

Scratching of polymers—Modeling abrasive wear

This paper aims to model abrasive wear for polymers using single-track and intersecting scratching techniques. Scratch and pin-on-disc wear tests were conducted on five different commercial polymers. Wear debris generated by multiple-pass single-track and intersecting scratching tests were compared and correlated with the specific wear rates of the same polymers in a pin-on-disk test using ground steel surface ( R a = 1.34 μm) as the counterface. It is the purpose of this paper to establish a correlation between scratching phenomenon and abrasive wear of polymers. Confirming previous studies, for polymers, the traditionally computed scratch hardness does not follow any trend with the abrasive wear. However, if the amount of wear debris in scratching is quantitatively measured and plotted against specific wear rate in pin-on-disc test, a reasonable linear relation is obtained.

Recurrent Morphology in the Scratching of Polymers

When a smooth sample surface is scratched by an indenter at constant normal load and driving speed, a macroscopically smooth groove is expected to be made on the surface. However, microscopically the scratch deformation is not stable, damage occurs intermittently along the scratching path so that recurrent morphology appears on the scratched surface. Examples of such morphology are described and deformation mechanisms are discussed together with the characteristics of horizontal force during the scratching of three polymers.