Investigation on the Effect of Different Pre-Cracking Methods on Fracture Toughness of RT-PMMA

At a Glance

Metadata	Details
Publication Date	2016-11-01
Journal	Latin American Journal of Solids and Structures
Authors	Elyas Haddadi, Naghdali Choupani, Farhang Abbasi
Institutions	Sahand University of Technology
Citations	12
Analysis	Full AI Review Included

Executive Summary

This document analyzes the research investigating the influence of eight different pre-cracking techniques on the measured Critical Stress Intensity Factor ($K_c$) of Rubber-Toughened PMMA (RT-PMMA). This study highlights the need for ultra-precise material removal methods, a core competency of 6CCVD.

Core Finding: The method of pre-crack insertion significantly altered the measured $K_c$, demonstrating a difference of up to 9% (0.24 MPa·m$^{0.5}$) between minimum and maximum results due to process-induced defects.
Key Factors: Fracture toughness sensitivity was primarily controlled by crack tip geometry (radius and width), Heat Affected Zone (HAZ), residual stress, and plastic deformation (crazing).
High-Precision Methods: Techniques relying on superhard materials (Cubic Boron Nitride/CBN disc, Diamond disc) and non-contact methods (Laser cutting) were essential for achieving reproducible, standard-compliant notch geometries.
Method Correlation: The Metal Slitting Saw achieved the maximum $K_c$ (2.77 MPa·m$^{0.5}$), attributed to compressive residual stress/plastic deformation. The highly sharp, low-defect Scoring method yielded the minimum $K_c$ (2.53 MPa·m$^{0.5}$).
6CCVD Relevance: This research underscores the demand for high-accuracy CBN and industrial diamond tools, and precision laser cutting services, all areas where 6CCVD provides superior materials and custom fabrication.

Technical Specifications

The following table extracts key quantitative data relevant to material performance and specialized processing parameters, focusing on diamond and CBN tools.

Parameter	Value	Unit	Context
Max $K_c$ (Fracture Toughness)	2.77 $\pm$ 0.09	MPa·m$^{0.5}$	Achieved by Metal Slitting Saw
Min $K_c$ (Fracture Toughness)	2.53 $\pm$ 0.06	MPa·m$^{0.5}$	Achieved by Scoring Method
Total $K_c$ Variation	~9% (0.24)	% (MPa·m$^{0.5}$)	Difference between max and min values
CBN Disc Diameter x Thickness	60 x 0.5	mm	Machining tool dimension
Diamond Disc Diameter x Thickness	22 x 0.2	mm	Machining tool dimension
Diamond Disc Machining Speed	400	rpm	Spindle Speed
Diamond Disc Feed Rate	12	mm/min	Material Removal Rate
Diamond Disc Crack Radius ($R$)	65	µm	Notch tip geometry
Diamond Disc Heat Affected Zone (HAZ)	40	µm	Process-induced defect size
Laser Cutting Power	50	W	Non-contact tool parameter
Specimen Dimensions (DENT)	70 x 25 x 0.8	mm$^{3}$	Double Edge Notched Specimen
Final Polishing Requirement	< 20	µm	Standard crack tip radius requirement (Reference)

Key Methodologies

The study utilized both contact (machining) and non-contact (laser) chip removal methods to create double-edge notched specimens in tension (DENT). High-precision CBN and diamond tools were critical components of the machining phase.

Material Compounding: PMMA (EG920) and G-ABS powder (85/15 wt/wt ratio) were melt compounded in an internal mixer at 220 °C and 60 rpm for 9 minutes.
Specimen Preparation: Samples (70 x 25 x 0.8 mm$^{3}$) were prepared via compression molding at 230 °C and 50 bars.
Pre-Cracking Procedures (Focus on Diamond/CBN/Laser):
- CBN Disc Machining: Utilized a CNC mill with a $\phi$60 x 0.5 mm CBN disc at 200 rpm and 12 mm/min feed rate, resulting in R300 µm crack tips and 40 µm HAZ.
- Diamond Disc Machining: Utilized a CNC mill with a $\phi$22 x 0.2 mm diamond disc at 400 rpm and 12 mm/min feed rate, resulting in R65 µm crack tips and 40 µm HAZ.
- Laser Cutting: Non-contact method using 50 W power and 20 mm/sec feed rate, achieving R65 µm tips but also creating a 40 µm HAZ.
Testing: DENT fracture tests were conducted using a Zwick/z10 machine at room temperature with a crosshead speed of 1 mm/min.
Qualitative Analysis: Notch regions and fracture surfaces were analyzed using Optical Microscopy (Olympus PMG3) and Scanning Electron Microscopy (SEM, Tescan MIRA3) after gold coating to assess defects (HAZ, deformation, crazing).

6CCVD Solutions & Capabilities

This research demonstrates that the quality of the pre-cracking tool and the control over the machining process directly dictate the accuracy and repeatability of critical material testing ($K_c$). 6CCVD provides the high-performance materials and custom fabrication necessary to overcome the manufacturing challenges identified in this paper.

Applicable Materials

To replicate or extend this research—particularly focusing on high-accuracy, low-damage material removal—6CCVD recommends the following materials for tool fabrication and process control:

Polycrystalline Diamond (PCD) Plates/Wafers: Ideal for manufacturing durable, precise industrial cutting tools (discs, blades, and scoring tips) with extremely low wear rates. 6CCVD offers custom PCD blanks up to 125mm in diameter.
Single Crystal Diamond (SCD) for Micro-Tooling: For generating ultra-sharp, near-zero defect crack tips (analogous to the CBN/Diamond discs used), high-purity SCD material can be fabricated into specialized micro-milling or scoring tools, offering unparalleled tip sharpness (Ra < 1 nm polished).
Heavy Boron-Doped Diamond (BDD) Film: Excellent for high-speed electrochemical or wear-resistant applications where PMMA or similar polymeric materials may be used.

Customization Potential

The experimental success hinges on achieving specific, reproducible tool geometries (e.g., Diamond Disc $\phi$22 x 0.2 mm, Razor thickness 0.11 mm, defined tip radii). 6CCVD specializes in providing materials and services tailored to these exacting engineering requirements:

Research Requirement (Tool)	6CCVD Capability	Benefits for Researchers
Thin Discs / Blades (0.1 mm - 0.5 mm)	Custom SCD/PCD thickness control from 0.1 µm up to 500 µm. We ensure tight dimensional tolerances for precision cutting edges.	Guaranteed uniformity and rigidity essential for high-accuracy chip removal methods.
Custom Diameter Tools	Wafers/Plates up to 125mm (PCD) available for cutting tool base material.	Supports large-scale or multi-format tool fabrication (e.g., $\phi$60 mm CBN analogue).
Precision Notching / Profiling	Custom Laser Cutting Services: Highly precise laser machining allows for the replication of complex notch geometries (e.g., R65 µm radius) without tool wear variations.	Eliminates mechanical stress and variability associated with traditional machining, offering superior control over HAZ vs. the 50 W laser method used in the study.
Minimizing Crack Tip Radius	Ultra-Fine Polishing (Ra < 1 nm SCD): Enables creation of cutting tools with crack tip radii significantly sharper than R65 µm, minimizing the influence of notch blunting on $K_c$ measurement.	Achieves crack tip quality necessary for ASTM/ESIS standards, reducing $K_c$ variability.
Surface Modification	Custom Metalization: We offer internal metalization (Ti/Pt/Au, W, Cu, Pd) for bonding diamond materials onto specialized tool shanks or mounting systems, ensuring tool integrity under high mechanical load.	Facilitates robust integration of diamond elements into CNC machining setups (as required for the Metal Slitting Saw/Diamond Disc methods).

Engineering Support

The variance in $K_c$ results (up to 9%) due to manufacturing defects (HAZ, residual stress, deformation) highlights the complexity of material processing. 6CCVD’s in-house PhD engineering team provides authoritative support for projects involving precise material removal and mechanical testing.

We assist engineers and scientists in optimizing material selection and processing parameters for fracture mechanics projects requiring:

Standard-compliant pre-cracking (e.g., aiming for crack tip radius < 20 µm).
Low-damage substrate processing (minimizing HAZ and residual stress).
High-throughput production of precision tools based on PCD or SCD.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Abstract In this study, eight techniques including coping saw, metal slitting saw, razor blade, cubic boron nitride (CBN) disc, scoring, die-cutting and guillotining, diamond disc, and laser cutting methods were used to produce pre-cracked fracture toughness (Kc) test specimens made of poly(methyl methacrylate)/graft-acrylonitrile butadiene styrene blends. The influences of notch shape (radial, rectangular, or angular-shaped and variety of thicknesses), pre-cracking method, chip removing or non-chip removing, and the contact or non-contact methods on the results obtained in fracture toughness tests were investigated. The results were analyzed by two methods, quantitatively and qualitatively, by comparing the obtained Kc results and studying the SEM and optical microscopy images, respectively. The results indicated that the different conditions of a produced pre-crack including; geometry of pre-crack due to geometry of tools, residual stress due to pre-crack creation, heat affected zone, damage of crack tip, and producing crazing around the crack tip could affect the fracture toughness. The maximum difference resulted from different pre-cracking methods was equal to 0.24 MPa.m0.5 and the lowest value of fracture toughness Kc, 2.53 MPa.m0.5, belonged to the scoring method but the highest value, 2.77 MPa.m0.5, belonged to the metal slitting saw method. Also, the results indicated that the effects of notching on toughness of RT-PMMA had a low notch sensitivity and the differences between minimum and maximum Kc values was found about 9%.

Tech Support

Original Source

DOI: https://doi.org/10.1590/1679-78252804

References

2010 - Laser cutting of polymeric materials: An experimental investigation [Crossref]
2008 - Some experimental studies on CO2 laser cutting quality of polymeric materials [Crossref]
2015 - On the processing and properties of clay/polymer nanocomposites CPNC [Crossref]
2015 - Effect of carbon nanotubes on laser cutting of multi-walled carbon nanotubes/poly methyl methacrylate nanocomposites [Crossref]
1984 - Size and loading mode effects in fracture toughness testing of polymers [Crossref]
2005 - Simple and accurate fracture toughness testing methods for pyrolytic carbon/graphite composites used in heart-valve prostheses [Crossref]
1989 - Time and temperature effects on the fracture toughness of rigid poly(vinylchloride) pipe materials