Marouen Hamdi - Academia.edu (original) (raw)

Papers by Marouen Hamdi

Polymer, 2020

The scratch resistance of polymeric materials is generally known to deteriorate with increasing t... more The scratch resistance of polymeric materials is generally known to deteriorate with increasing temperature of testing. The present study focuses on quantitatively predicting the effect of temperature on the scratch behavior of amorphous polymers. The Arruda-Boyce viscoplastic model is utilized to account for temperature and strain rate dependent strain-softening and strain-hardening behaviors. The post-yield behavior predicted in this model is calibrated using the yield point determined by the Richeton cooperative model. The pressure dependent Drucker-Prager model with calibrated post-yield experimental data at various strain rates is chosen as the plastic constitutive relationship of the polymeric systems for FEM simulation. Furthermore, temperature and pressure dependent frictional behavior is input into an ABAQUS contact model to simulate the variation of the adhesion coefficient of friction (μ a) during the ASTM standardized linearly increasing load scratch test. The FEM simulation findings show a good agreement with the experimentally determined scratch depth and scratch coefficient of friction (SCOF) measured using the scratch test. Usefulness of the present study for design of scratch resistant polymers at elevated temperatures is discussed.

Wear, 2020

Mar is a type of subtle surface damage caused by a sliding object barely visible to human eyes. T... more Mar is a type of subtle surface damage caused by a sliding object barely visible to human eyes. This minor damage phenomenon has rarely been systematically studied. Significant research efforts for the fundamental understanding of mar behavior in polymers are still needed. In this study, the mar behavior of a series of model amorphous polymers, i.e., polymethylmethacrylate (PMMA), polycarbonate (PC), and polystyrene (PS), were investigated based on a modified ASTM/ISO scratch testing methodology and a corresponding finite element method (FEM) modeling. Furthermore, the mar-induced visibility and material parameter relationships were established through a systematic FEM parametric study. Experimental results show that PMMA has the highest mar visibility resistance, indicated by lower surface roughness variation and low contrast between marred region and the background. The numerical analysis showed that the maximum principal plastic strain (e1p) and total dissipated plastic energy (Ep) can be considered for evaluating mar visibility resistance. Higher mar visibility resistance corresponds to lower e1p and Ep values. Based on these two criteria, the parametric analysis shows that mar visibility resistance increases with lower modulus, higher yield stress, higher hardening slope, and lower softening slope. The usefulness of the present study for the preparation of mar resistant polymers is discussed.

Polymer Testing, 2018

A key aspect of the perceived quality of polymeric materials is their resistance to visible scrat... more A key aspect of the perceived quality of polymeric materials is their resistance to visible scratch and mar damage. An effective set of testing and evaluation tools is needed for quantitative assessment of scratch and mar damage on polymer surfaces, which is critical for the development of scratch and mar resistant polymers. Mar damage is particularly challenging to quantify because the damage is subtle and is sensitive to imaging techniques, especially for white and transparent samples. In this study, a mechanical procedure for marring white and transparent polymeric films in a reproducible fashion that allows for study of the fundamental materials science is introduced. In the second stage of the process, an optical imaging instrument that exposes the marred films to light in a manner mimicking how our eyes perceive the mar damage is used. Finally, a machine-vision procedure is used for handling the images and quantitatively measuring the visibility due to surface damage. A good correlation is found between the machine-vision and the perceptions of a human panel. This methodology is useful for quantitatively assessing resistance of a sample to mar damage. It can also be used for establishing structure-property relationships between polymer material/surface characteristics and mar damage.

Polymer, 2017

A facile but efficient spray-coating method was recently developed to manufacture thin, flexible,... more A facile but efficient spray-coating method was recently developed to manufacture thin, flexible, and transparent epoxy films reinforced with well-exfoliated and highly-aligned a-zirconium phosphate (ZrP) nanoplatelets in smectic liquid crystalline order. Here, we investigate the scratch resistance of ZrP/epoxy nanocomposites prepared following the same spray-coating process. Comparison was made with neat epoxy coating to determine the impact of ZrP nanofillers. Tests were conducted with accordance to ASTM D7027/ISO 19252 scratch standard and scratch mechanisms were studied using different experimental tools. Results show that scratch resistance is considerably improved after introducing ZrP nanofillers to the epoxy coating. This was reflected by the delay in microcracking and plowing damages and the decrease of scratch coefficient of friction. This result is attributed to the significant role of exfoliated and aligned ZrP nanofillers in enhancing the mechanical properties of the epoxy matrix. The usefulness of the current study in developing new coating systems for high-performance applications is discussed.

SAE International Journal of Materials and Manufacturing, 2017

Wear, 2017

In this study, we present an experimental and numerical investigation on scratch behavior on mode... more In this study, we present an experimental and numerical investigation on scratch behavior on model polymeric films and laminates. The studied model systems consist of polyamide 6 (PA) and polypropylene (PP) films, and PA/PP and PP/PA laminates. Experimental findings, conducted according to ASTM/ISO standard, demonstrate that PP/PA laminate has better scratch performance than PA/PP. This is explained by low surface friction, characteristic constitutive behavior, and graded structure of PP/PA laminate. The scratch test was numerically simulated using a sophisticated FEM model to gain more mechanistic insight. The scratch features observed experimentally were well-captured using the FEM model, demonstrating the consistency between the experimental and numerical analyses. Low PA/PP scratch resistance is associated with high stress concentration at the laminate-substrate interface, leading to significant interfacial failure. Similarly, good PP/PA resistance is related to suppressed interfacial stresses due to effective dissipation of scratch energy by upper PP layer and the shielding of delamination from the substrate by the lower strong and stiff PA layer. This study provides guidelines for the design of scratch-resistant polymeric films and laminates.

Tribology International, 2016

Polypropylene films are extensively used in many applications and susceptible to various tribolog... more Polypropylene films are extensively used in many applications and susceptible to various tribological damages like scratch. To improve their resistance to these damages, their mechanical properties can be modified through different approaches. In this study, we investigate the effects of molecular orientation and architecture, modified through the incorporation of ethylene comonomer, on the scratch resistance of polypropylene-based films using a standardized scratch testing methodology and FEM simulation. Results show that film tensile properties increase with higher orientation and lower ethylene comonomer, improving the scratch resistance. This improvement is associated with stress concentration shift from the interface toward the surface, and caused mainly by higher yield stress and strain hardening. Approach for designing polymeric films with better scratch performance is discussed.

Materials & Design, 2015

Scratch and mar can critically impact the aesthetics of polymeric surfaces. Their quantification ... more Scratch and mar can critically impact the aesthetics of polymeric surfaces. Their quantification poses considerable challenges, especially for subtle mar damages. Here, we report a new standardized approach that utilizes a modified ASTM/ISO scratch test standard and a psychophysical tool to quantify scratch and mar visibility. The new methodology was then used to study the influence of color, gloss, and texture perception on scratch and mar visibility resistance. These factors have limited influence on scratch visibility onset. However, faint mar damage is more sensitive to surface perceptual properties. It has been found that overall visibility throughout the entire damage path is a better indicator for ranking mar damage. Results show that contrast slope variation parameter can consistently quantify mar visibility and simulate human perception. Green, glossy, and smooth surfaces tend to have less mar visibility resistance. The effect of a fatty amide slip agent was also investigated. These modifiers improved both scratch and mar visibility resistance. This unique approach paves the way for a straightforward universal standard that can be utilized to reliably quantify scratch and mar visibility in polymers, thereby opening up a new avenue for the design of polymeric materials with better scratch and mar visibility resistance.