ASTM D7337 is a standard test method for tensile creep-rupture testing of fiber-reinforced polymer (FRP) matrix composite bars. The test determines an FRP bar’s capacity to withstand a certain fraction of its short-term tensile strength without failure. The standard covers creep-rupture testing of FRP bars used as internal reinforcement in concrete, such as GFRP rebar, CFRP rebar, and FRP prestressing tendons. Engineers use the test method results when designing FRP reinforcements subjected to sustained loading. The fundamental test result is the creep rupture strength of the test piece after one million hours.
ASTM D7337 Tensile Creep Rupture of Fiber-Reinforced Polymer Matrix Composite Bars
What is ASTM D7337?
What is the Scope of the ASTM D7337 Test Standard?
ASTM D7337 provides the procedures for tensile creep rupture testing of fiber-reinforced polymer matrix (FRP) composite bars as tensile elements in reinforced, prestressed, or post-tensioned concrete. This test method is used to measure the tensile creep-rupture strength of an FRP composite bar that is subjected to continuous axial loading for an extended period of time. The standard includes requirements for specimen preparation, load application, environmental requirements, and data analysis. The scope of ASTM D7337 includes:
- Material type: Fiber-reinforced polymer (FRP) matrix composite bars, mainly GFRP and CFRP rebar.
- Purpose: Material specification, research and development, quality assurance, and structural design and analysis.
- Property measured: Creep rupture time and million-hour creep rupture capacity of FRP bars under sustained axial tensile loads.
- Method: Applying a constant tensile load to FRP bar specimens until they break or until the specified time limit is reached.
- Result: Time-to-failure data plotted on a log-log plot to form the creep rupture envelope to predict performance for design service lifetimes.
- Test Limitations: This standard does not attempt to cover all safety aspects of its use.
- Units: Values in SI and inch-pound units are each considered standard.
What are the Uses of ASTM D7337 Testing?
ASTM D7337 is a test to determine the creep rupture characteristics of fiber-reinforced polymer composite bars under an applied stress for a specified duration. The test results are used for quality control, material verification, research and development, and structural design and analysis. It is applied in many industries such as construction, automotive, aerospace, and marine. This standard-
- Carries out the creep rupture test of FRP bars under a controlled environment and force ratio.
- Evaluates long-term structural performance and durability of composite materials.
- Supplies information to forecast service life and maximum allowable sustained stresses.
- Complies with quality assurance and materials specifications.
- Allows structural design and analysis of FRP reinforcements under constant load.
- Provides assistance to design engineers in determining the stress limits for FRP reinforcement for a service life of 50-100 years.
- Feeds into the ACI 440.1R and CSA S807 design guidelines.
Which materials can be tested under ASTM D7337?
ASTM D7337 is applicable to fiber-reinforced polymer (FRP) matrix composite bars meeting the ASTM definitions for glass fiber reinforced polymer (GFRP) rebar and carbon fiber reinforced polymer (CFRP) rebar used as internal reinforcement in concrete structures. The standard also applies to FRP prestressing tendons. These materials typically consist of carbon fibers, glass fibers, or aramid fibers combined with a polymer matrix. Their high strength-to-weight ratios and resistance to corrosion are crucial for maintaining the structural integrity when subjected to mechanical and environmental stresses.
Why is ASTM D7337 Important?
ASTM D7337 provides a standardized method for testing tensile creep rupture of fiber-reinforced polymer composite bars. Unlike steel reinforcing bars subjected to significant sustained stress, creep rupture of FRP bars may take place below the static tensile strength. Thus, the creep rupture strength is one of the important properties to consider when determining acceptable stress levels in concrete members reinforced with FRP bars and subjected to sustained loads. The creep rupture strength depends on the type of FRP bars used. The standard provides uniformity in test procedures and interpretation of test data across laboratories. Structural engineers use this standard to guarantee that modern structures created with FRP composite materials are safe and durable.
ASTM D7337 Equipment and Sample Preparation Guide
ASTM D7337 calls for using a universal testing machine with suitable gripping fixtures to apply and hold a sustained tensile load on FRP bar specimens. Technicians carefully prepare representative specimens in laboratories for tensile creep rupture testing and subsequent evaluation. The equipment includes a testing machine with force capacity exceeding the specimen’s tensile capacity, gripping fixtures or anchorages to prevent specimen damage, an environmental chamber for temperature control, and a data acquisition system.
| Sample and Specimen Details | The test specimens consist of FRP composite bars made with GFRP, CFRP, or aramid fibers and must represent the production lot. The principal variable is the size or type of FRP bar. |
| Specimen Preparation | Technicians clean and prepare specimens as per requirements. They ensure specimens are free from surface defects. They protect the specimens from grip damage using appropriate end-tabs or anchorages |
| Specimen Dimensions | The acceptable specimen size varies with testing requirements. The specimen length must accommodate the gripping system and gauge length for deformation measurement. |
| Instrumentation | Universal testing machine (force capacity exceeding specimen tensile capacity), gripping fixtures or anchorages, environmental chamber (for controlled temperature), data acquisition system, extensometer or displacement measurement device, timer for recording time to rupture. |
Testing Procedures and Requirements for ASTM D7337
ASTM D7337 testing confirms that the tensile creep rupture properties of FRP composite bars are tested in a standard manner. Analysts follow standardized procedures to ensure reliable, accurate results. The technicians prepare specimens, apply sustained tensile loads, continuously monitor the test, and record the results. The ASTM D7337 test method comprises the following test procedure:
| Specimen Preparation | Technicians clean and prepare FRP bar specimens to specified dimensions. They attach end-tabs or anchorages to prevent grip damage. They measure and record initial specimen dimensions. |
| Specimen Mounting | Technicians mount the specimen in the testing machine with proper alignment. They ensure secure gripping to prevent slippage during testing. |
| Load Application | Technicians apply the specified sustained tensile load (typically 20–70% of short-term tensile strength). They maintain the load constant throughout the test duration |
| Data Recording | The system continuously records time, load, and deformation. Technicians monitor the specimen for signs of rupture or failure. They document the time to rupture. |
| Result Analysis | Analysts plot time-to-failure data on a log-log scale to construct the creep-rupture envelope. They extrapolate the data to predict million-hour creep rupture capacity. |
ASTM D7337 Testing Process and Data Collection
The testing process starts with preparing the FRP bar specimen to the required dimensions. Technicians clean the specimen and attach end tabs or anchorages to prevent grip damage. They mount the specimen in the testing machine with proper alignment. They apply the specified sustained tensile load and keep it constant throughout the test period. The system continuously records time, load, and deformation. Technicians monitor the sample for failure and note the failure time. The creep-rupture envelope is a plot of several sets of time-to-failure data for each load level on a log-log scale. With this information, they extrapolate a prediction of the specimen’s million-hour creep rupture strength. Laboratories gather data to ensure quality, verify materials, conduct research and development, and support structural designs.
Common Challenges and Troubleshooting
Typical problems during ASTM D7337 testing include composite bar misalignment, maintaining consistency in the environment, fixture problems, equipment compliance problems, and grip or end-tab damage. Such problems may impact the validity of creep rupture calculation. Improper alignment results in non-uniform stress distribution. Inconsistent environmental conditions may impact material behavior and test results. When the grips fail before the gauge section, it’s due to grip or end-tab damage. Difficulty is minimized by proper specimen preparation, properly aligned specimens, proper calibration of testing machines, and appropriate gripping systems. The use of standard operating procedures and the proper maintenance of equipment provide for reliable results, as is the case with experienced technicians.
ASTM D7337 Analysis Results and Interpretation
The report presents a summary of the tensile creep-rupture properties of the tested specimen of the FRP composite bar. It presents the measured results of the parameter(s) specified, with units and specimen information. The interpretation then benchmarks these measured values to specification requirements or performance benchmarks. These results are used by structural engineers to check the compliance of the material and ensure the performance of the products.
- The laboratory reports the time to rupture at each load level.
- The laboratory constructs the creep-rupture envelope on a log-log scale.
- Analysts use the extrapolated data to calculate the million-hour creep rupture capacity.
- Results show the ability of the FRP bar to sustain load.
- The laboratory offers performance comparisons to specifications.
- The laboratory records test conditions and specimen data.
- Consistent specimen preparation, proper alignment, and calibrated equipment help laboratories produce reliable results.
Get Certified ASTM D7337 Testing for Reliable Composite Material Analysis
Certification helps ensure fiber-reinforced polymer composite bars undergo accurate testing using standardized tensile creep rupture procedures. Using composite materials in applications such as the automotive, construction, aerospace, and marine sectors requires an experienced laboratory testing group to evaluate composite durability and long-term structural reliability. ASTM D7337-certified testing is used for quality control, material verification, research and development, and structural design and analysis. Professional laboratory services ensure adherence to the standard requirements, and this gives them confidence in the test results. In critical infrastructure projects, certified testing is essential to ensure the safety and integrity of materials, which is crucial for structural engineers and quality control experts.
FAQ
What is the principle behind ASTM D7337?
The test method involves putting a sustained tensile load on FRP bar specimens until they fail or a time limit is reached. The data from the time-to-failure tests conducted under different loads are plotted on a log-log graph to create the creep-rupture envelope.
What materials can be tested under ASTM D7337?
ASTM D7337 is for fiber-reinforced polymer (FRP) bars such as GFRP and CFRP rebar for internal reinforcement in concrete constructions and FRP prestressing tendons.
What is the primary test result of ASTM D7337?
The most important test result is the creep rupture life of the specimen in one million hours. This value is calculated in accordance with a procedure described in Annex A1 of the standard.
How are ASTM D7337 results reported?
Analysts report the rupture times for each stress level and plot the creep-rupture envelope on a log-log graph. The laboratory offers the 1,000,000-hour creep-rupture capacity, performance verification in relation to specifications, and a compliance statement report.
Updated on September 17, 2026
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