Resin fiberglass board impact strength testing is a core quality-control procedure used to evaluate the toughness and fracture resistance of glass-fiber-reinforced thermoset laminates such as FR-4, G10, G11, and EP GC grades. This article explains the applicable ISO, ASTM, IEC, GB, and JIS standards, specimen preparation requirements, Charpy and Izod test procedures, and the key factors that influence test results. Whether you are a PCB fabricator, insulation component manufacturer, or design engineer, understanding impact strength testing helps ensure material reliability and regulatory compliance.
Technical Overview
Resin fiberglass board, also known as glass-fiber-reinforced resin laminate, epoxy glass cloth laminate, or GFRP laminate sheet, is a composite material manufactured by impregnating woven glass fabric or glass mat with a thermosetting resin (typically epoxy, polyester, or phenolic) and curing the layup under heat and pressure. Common commercial grades include FR-4, G10, G11, 3240 epoxy glass cloth laminate, and the EP GC series defined in IEC 60893-3-2 and GB/T 1303.2.
Impact strength testing quantifies the ability of the laminate to absorb energy under rapid, high-strain-rate loading. Because thermoset matrices are inherently brittle and the embedded glass fibers introduce strong anisotropy, resin fiberglass boards may fail through matrix cracking, fiber breakage, or interlaminar delamination when subjected to shock loads during machining, assembly, transport, or service. Standardized pendulum impact tests, primarily the Charpy method (ISO 179-1, ASTM D6110, GB/T 1043.1, JIS K 7110) and the Izod method (ISO 180, ASTM D256, GB/T 1843, JIS K 7111), provide reproducible measures of notched and unnotched impact resistance for material qualification, incoming inspection, and design verification. These tests are routinely performed by accredited third-party laboratories as part of material certification.
Testing Samples
Charpy Impact Specimens (ISO 179-1 / GB/T 1043.1)
The preferred Charpy specimen is a rectangular bar of 80 mm length, 10 mm width, and 4 mm thickness. Specimens may be tested edgewise (e), with the impact applied parallel to the thickness direction, or flatwise (f), with the impact applied parallel to the width direction. Notches, when required, are machined at the mid-length of the specimen; type A notches have a radius of 0.25 mm, type B notches 1.00 mm, and type C notches 0.10 mm, each cut to a depth of 2.0 mm so that a residual width of 8.0 mm remains. Test designations such as 1eU (unnotched, edgewise) or 1eA (A-notched, edgewise) are used to identify the test configuration.
Izod Impact Specimens (ISO 180 / ASTM D256 / GB/T 1843)
For the Izod method, ISO 180 and GB/T 1843 use specimens of 80 mm × 10 mm × 4 mm with a machined notch, tested edgewise as a vertical cantilever. ASTM D256 specifies a specimen of 63.5 mm length, 12.7 mm width, and 3.2 mm preferred thickness, with a 2.54 mm deep notch (0.25 mm radius) leaving a 10.16 mm residual width. For resin fiberglass boards thicker than about 10 mm, specimens are normally machined to the standard cross-section with the laminate surface retained, or tested edgewise to preserve the original layered structure.
Specimen Preparation and Conditioning
Specimens shall be cut from representative production sheets with the specimen axis aligned to the machine (warp) or transverse (weft) direction, as agreed between purchaser and supplier. Machining must avoid overheating, chipped edges, and delamination, and notch roots must be free of visible cracks or melting. Unless otherwise specified, specimens are conditioned in the standard atmosphere of 23 ± 2 °C and 50 ± 5 % relative humidity per ISO 291, typically for a minimum of 88 hours before testing. At least five, and preferably ten, specimens are tested for each orientation and notch condition.
Testing Items
Typical impact strength test items for resin fiberglass boards include:
- Charpy impact strength, unnotched, edgewise and flatwise (kJ/m²)
- Charpy impact strength, notched with A-type or B-type notch (kJ/m²)
- Izod impact strength, notched and unnotched (kJ/m² per ISO, or J/m and ft·lb/in per ASTM D256)
- Tensile impact strength per ISO 8256, where high-rate tensile loading is relevant
- Instrumented falling-dart puncture impact per ISO 6603-2 or ASTM D5628 for sheet products exposed to localized impact
- Fracture classification per ISO 179-1: complete break (C), hinged break (H), partial break (P), or non-break (N)
Testing Methods
Charpy Impact Test Procedure
The specimen is placed horizontally on two anvils spaced 62 mm apart and is struck at mid-span by the pendulum of a calibrated impact tester. The hammer capacity is selected so that the absorbed energy is between 10 % and 80 % of the nominal energy of the pendulum; measured energies are corrected for friction and windage losses in accordance with ISO 179-1. The tester displays the absorbed energy, and the specimen fracture mode is recorded after each strike.
Izod Impact Test Procedure
The notched specimen is clamped as a vertical cantilever with the notch positioned on the tension side facing the striker. The pendulum strikes the specimen at a point 22 mm above the notch line (ISO 180) or at the prescribed distance from the clamping jaw (ASTM D256). The absorbed energy is read directly and corrected for system losses; brittle, hinged, or partial fractures are noted because non-break results must be reported separately rather than averaged.
Calculation and Data Expression
Under the ISO and GB methods, impact strength equals the corrected absorbed energy divided by the cross-sectional area of the specimen, expressed in kJ/m²; for notched specimens, the residual width beneath the notch is used in the calculation. Under ASTM D256, Izod impact resistance is the absorbed energy per unit width of the specimen, expressed in J/m or ft·lb/in. Test reports identify the standard used, specimen orientation, notch type, individual values, the arithmetic mean, the fracture classification, and the conditioning and test atmospheres, for example: Charpy impact strength, 1eA = X kJ/m², complete break.
Factors Influencing Test Results
- Fiber orientation: strength measured along the warp direction typically differs significantly from the weft direction due to the woven glass cloth reinforcement.
- Test direction: edgewise and flatwise results differ because impact can drive cracks between laminate plies, promoting delamination.
- Notch quality: notch radius accuracy, cutter sharpness, and root defects strongly affect notched values.
- Laminate construction: resin content, glass cloth grade, number of plies, cure degree, and void content all influence energy absorption.
- Environment: test temperature and humidity, and the conditioning history of the specimen.
- Instrument parameters: pendulum capacity, support span, and striking-edge geometry.
As general guidance, unnotched Charpy impact strength of epoxy glass cloth laminates commonly falls in the range of tens of kJ/m², while A-notched values are typically an order of magnitude lower; exact acceptance values depend on grade and must be taken from the material specification or purchase agreement.
Applications
Impact strength data for resin fiberglass boards are used across many industries and product categories:
- Printed circuit board substrates: qualification of FR-4 laminates for rigid PCBs that must survive drilling, scoring, assembly, and rework shocks.
- Electrical insulation: verification of EP GC and 3240 grade boards used in switchgear, transformer brackets, busbar supports, and insulating barriers per IEC 60893 and GB/T 1303.
- Structural components: panels, spacers, gears, and wear parts in railway, marine, and general machinery applications where shock loading is expected.
- Automotive and aerospace: lightweight composite supports and insulating structures requiring documented impact performance at room and low temperature.
- Quality control and failure analysis: incoming material inspection, supplier comparison, batch conformity checks, and root-cause investigation of cracked or delaminated parts.
Test reports issued by accredited third-party laboratories are widely accepted for customer qualification, export documentation, and compliance demonstrations against ISO, IEC, ASTM, EN, GB, UL, and JIS requirements.
FAQ
What is the difference between the Charpy and Izod impact tests?
In the Charpy test the specimen lies horizontally on two supports and is struck at mid-span (ISO 179-1), whereas in the Izod test the specimen is clamped vertically as a cantilever and struck above the notch (ISO 180, ASTM D256). The two methods use different specimen geometries and clamping conditions, so results are not directly interchangeable.
Why are notched specimens tested?
A machined notch creates a controlled stress concentration that initiates crack propagation and measures resistance to brittle crack growth. Notched results reveal sensitivity to sharp defects, while unnotched results reflect the overall energy absorption of the laminate.
Which standards apply to FR-4 resin fiberglass boards?
Impact testing is generally performed to ISO 179-1/ISO 180 or ASTM D256, while material property requirements for epoxy glass laminates, including minimum impact values, are defined in IEC 60893-3-2 and GB/T 1303.2. The applicable standard should be agreed upon before testing.
How does fiber orientation affect impact strength?
Because glass cloth is woven and anisotropic, specimens cut along the warp direction usually show different impact energy than those cut along the weft direction. Impact perpendicular to the laminate plane can also trigger delamination, so both edgewise and flatwise orientations may need to be evaluated.
What result indicates pass or fail?
There is no universal pass threshold. The measured mean impact strength is compared with the minimum value stated in the material specification, purchase contract, or product standard for the declared grade, orientation, and notch condition, together with the required fracture classification.
Can impact testing be performed at low temperature?
Yes. Tests can be conducted at sub-zero or elevated temperatures using conditioned chambers on the pendulum tester, which is common for outdoor electrical insulation and cold-environment applications, since thermoset laminates become more brittle at low temperature.