ASTM D7750-23

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Designation: D7750 − 12 (Reapproved 2017) D7750 − 23
Standard Test Method for
Cure Behavior of Thermosetting Resins by Dynamic
Mechanical Procedures using an Encapsulated Specimen
Rheometer
This standard is issued under the fixed designation D7750; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This method covers the use of dynamic mechanical instrumentation for determination and reporting of the thermal
advancement of cure behavior of thermosetting resin on an inert filler or fiber in a laboratory. It may also be used for determining
the cure properties of filled resins and resins without reinforcements.without fillers or fibers. These encapsulated specimens are
deformed in torsional shear using dynamic mechanical methods.
1.2 This method is intended to provide means for determining the cure behavior of thermosetting resins on fibers over a range of
temperatures from room temperature to 250°C250 °C by forced-constant amplitude techniques (in accordance with Practice
D4065). Plots of complex modulus, complex viscosity, and damping ratio or tan delta as a function of time or temperature, or both,
quantify the thermal advancement or cure characteristics of a resin or a resin on filler or fiber.
1.3 Test data obtained by this method is relevant and appropriate for optimizing cure cycles.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4.1 Exception—The fahrenheitFahrenheit temperature measurement in 10.1 is provided for information only and is not
considered standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D3878 Terminology for Composite Materials
This test method is under the jurisdiction of ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.03 on
Constituent/Precursor Properties.
Current edition approved Aug. 1, 2017April 1, 2023. Published September 2017May 2023. Originally approved in 2012. Last previous edition approved in 2017 as
D7750–12. DOI: 10.1520/D7750-12R17. – 12 (2017). DOI: 10.1520/D7750-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7750 − 23
D4000 Classification System for Specifying Plastic Materials
D4065 Practice for Plastics: Dynamic Mechanical Properties: Determination and Report of Procedures
D4092 Terminology for Plastics: Dynamic Mechanical Properties
D4473 Test Method for Plastics: Dynamic Mechanical Properties: Cure Behavior
D6507 Practice for Fiber Reinforcement Orientation Codes for Composite Materials
D7028 Test Method for Glass Transition Temperature (DMA Tg) of Polymer Matrix Composites by Dynamic Mechanical
Analysis (DMA)
E380 Practice for Use of the International System of Units (SI) (the Modernized Metric System) (Withdrawn 1997)
3. Terminology
3.1 Definitions: For most definitions applicable to this method refer to Terminology D4092.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 Encapsulated Sample Parallel Plate Rheometer—Dynamic Mechanical Analyzer apparatus that holds the specimen under
pressure within a confined cavity. The apparatus is designed to contain the resin within the specimen throughout the progress of
the cure.
4. Summary of Test Method
4.1 A small circular specimen is assembled from uncured thermoset resin materials that correspond to a representation of a
composite part. This specimen is placed in mechanical oscillation at a fixed frequency at either isothermal conditions, a linear
temperature increase or a time-temperature relation simulating a processing condition. The lower plate oscillates and transmits
torque from the lower plate through the sample into the upper plate. The resulting torque measured at the upper plate is converted
to shear modulus using equations that compensate for the shape and size of the sample. The shear modulus is separated into a
component that is in phase with the applied strain or elastic shear modulus and a component that is 90° out of phase with the
applied strain or loss shear modulus. The elastic and loss modulus of the specimen are measured as a function of time. During cure,
the elastic shear modulus will initially decrease as the temperature is increased due to a decrease in the viscosity of the resin in
the sample. When cure occurs in the sample, the elastic shear modulus increases.
5. Significance and Use
5.1 This method provides a simple means of characterizing the cure behavior of a thermosetting resin specimen that is a
representation of a composite part. The diameter of the specimen is approximately 38 mm 38 mm and the thickness ranges from
3 3
2.6 to 3.2 mm. 2.6 mm to 3.2 mm. This corresponds to a sample volume of approximately 33 cm to 4 cm4 cm . The data may
be used for quality control, research and development, and verifying the cure within processing equipment including autoclaves.
5.2 Dynamic mechanical testing provides a sensitive method for determining cure characteristics by measuring the elastic and loss
moduli as a function of temperature or time, or both. Plots of cure behavior and tan delta of a material provide graphical
representation indicative of cure behavior under a specified time-temperature profile. The presence of fibers within the resin may
change the dynamic properties measured within a material. However, it is still possible to compare different resins with the same
fiber structure and obtain the relative difference due to the resin cure properties.
5.3 This method can be used to assess the following:
5.3.1 Cure behavior, as well as changes as a function of temperature or time, or both,
5.3.2 Processing behavior, as well as changes as a function of temperature or time, or both,
5.3.3 The effects of processing treatments,
5.3.4 Relative resin behavioral properties, including cure behavior, damping and impact resistance,
5.3.5 The effects of reinforcement on cure.cure; the reinforcement can be a fiber or a filler,
The last approved version of this historical standard is referenced on www.astm.org.
D7750 − 23
5.3.6 The effects of materials used to bond the resin and reinforcement,
5.3.7 The effect of formulation additives that might affect processability or performance.
5.4 This provides a method to assess the cure properties of a thermosetting resin containing woven fiber or other reinforcing
materials.
5.5 This method is valid for a wide range of oscillation frequencies typically from 0.002 to 50 Hz.0.002 Hz to 50 Hz.
NOTE 1—It is recommended that low-frequency test conditions, generally 1 to 2 Hz, 1 Hz to 2 Hz, be used to generate more definitive cure-behavior
information. Slower frequencies will miss important cure properties. Faster frequencies will reduce sensitivity to cure.
6. Interferences
6.1 Apparent discrepancies in results may arise when using different experimental conditions. These apparent differences from
results observed in another study can usually be reconciled without changing the observed data, by reporting in full (as described
in this method) the conditions under which the data were obtained. One essential condition within this method that must be noted
is the presence of pressure within the specimen chamber which ensures good precision.
6.2 In many cases, the specimens made with this method will be significantly smaller than the parts in production. It is essential
that specimens be made from representative samples of uncured material used to make parts. This will ensure that the data is
representative of the part cure.
6.3 The result is a response to the thermal advancement or cure behavior of the resin. The cure behavior is also influenced by the
reinforcement and materials used to enhance the bond between the resin and reinforcement. The reinforcement can be a fiber or
a filler.
6.4 The data will represent the cure of the system at the measured temperature. Parts are often significantly thicker than the
specimen. There may be a significant difference between the temperature versus time profile on the inside and the outside of those
composite parts. Thermocouples can be used to measure both temperatures during a cure process of a thick part. The measured
temperature versus time data can be used to define temperature versus time profiles for dynamic cure specimens using the
procedures of this standard. The results can be used to compare the cure response for the inside and the outside of the composite
part.
7. Apparatus
7.1 The function of the apparatus is to hold a resin specimen with inert reinforcement, such as fibers, under pressure and yet
prevent the escape of resin. Thereby, the fiberreinforcement to resin ratio will remain constant throughout the test. The material
acts as the elastic and dissipative element in a mechanically driven oscillatory shear system. This dynamic mechanical instrument
operates in torsional shear using one of the following modes for measuring cure behavior:
7.1.1 Forced, constant amplitude, fixed frequency,
7.1.2 Forced, variable amplitude, fixed frequency.
7.2 The apparatus shall consist of the following:
7.2.1 Parallel plates with serrated or radial grooved surfaces. The diameter of the dies shall be 40 6 2 mm. 40 mm 6 2 mm. The
depth of the grooves shall be limited to 1.0 mm 1.0 mm or less to keep a constant fiberreinforcement to resin ratio.
7.2.2 Encapsulated Specimen Cavity—The specimen shall be encapsulated by the two parallel plates and a series of mechanical
components at the outer plate diameter designed to contain the specimen under pressure without loss of resin. These components
shall include an O-ring inserted at the outer diameter of the specimen (Fig. 1). The O-ring meets ASTM International size No.
2-127.
D7750 − 23
FIG. 1 Encapsulated specimen parallel plate rheometer plate system designed to keep a constant fiberreinforcement to resin ratio dur-
ing a test.
7.2.3 Plate Gap—The thickness of the sample shall range from 2.6 to 3.2 mm. 2.6 mm to 3.2 mm. The calculation of the sample
modulus will include corrections to the actual sample thickness.
7.2.4 Plate Closing Mechanism—The system shall apply a pressure of at least 4200 kPa 4.2 MPa to the sample to prevent slippage.
7.2.5 Plate Oscillating System (Strain Device)—The plate oscillating system shall consist of a direct drive motor that imparts a
torsional oscillating movement to the lower plate in the cavity plane. The movement shall produce a continuous oscillatory
deformation (strain) on the specimen. The deformation (strain) shall be sinusoidal and shall be applied and released continuously
as in a forced-vibration device (see Table 1 of Practice D4065) to provide a continuous measurement of material state. The
preferred amplitude ranges shall be from 6 0.0050.005° to 6 0.060°. The resulting strain at the nominal specimen thickness will
range from 6 0.070.07 % to 6 0.8 %.0.8 %.
NOTE 2—The preferred strain for measuring the cure properties of thermoset resins is 6 0.7 %.
7.2.6 Detectors—A device or devices for determining dependent and independent experimental parameters, such as torque,
frequency, strain amplitude and temperature. Temperature shall be measurable with a precision of 6 0.3°C0.3 °C at the outer
diameter of the plate, frequency to 60.16 0.1 % and torque to 6 0.001 Nm.
7.2.7 Temperature Controller—A device for directly heating and cooling the plates with the ability to control the temperature of
the plates. The temperature can increase in steps or a linear ramp or cool in steps or a linear ramp. Fig. 2 illustrates a typical
time-temperature profile for measuring cure properties. A temperature control system shall be sufficiently stable to permit
measurement of plate temperature to within 6 0.3°C0.3 °C during heating and 6 1°C1 °C during cooling. Fig. 2 also shows that
the temperature in the part often deviates from the recommended temperature profile. The apparatus shall process a specimen using
either the recommended temperature profile or the actual temperature profile in the part depending on the specification of the test
requestor. The report shall contain a comment indicating which type of temperature profile was used.
7.3 The system must have instrument compliance compensation to ensure a good measure for the final modulus values during
cure.
8. Sampling and Test Specimens
8.1 The neat resin or the resin with reinforcement should be representative of the polymeric material being tested. If reinforcement
is present in the resin, it shall be inert and the dynamic properties of the reinforcement shall not be affected by the temperature
used for the dynamic cure test. However, if the presence of reinforcement within the resin may change the dynamic properties
measured within a material, it is still possible to compare different resins with the same fiber structure and obtain the relative
difference due to the resin cure properties (5.2).
8.2 The recommended specimen diameter for this apparatus is 38 6 0.5 mm 38 mm 6 0.5 mm (Fig. 3) or a diameter
recommended by the apparatus manufacturer. Several 38-mm38 mm disks of uncured material shall be laid up to produce a
specimen for testing. The reinforcement type and lay-up shall be recorded in accordance with the laminate orientation code of
Practice D6507. The number of disks required to produce a specimen
...