ASTM D6112-23
Standard Test Methods for Compressive and Flexural Creep and Creep-Rupture of Plastic Lumber and Shapes
- Standard No.
- ASTM D6112-23
- Release Date
- 2023
- Published By
- American Society for Testing and Materials (ASTM) US / ASTM
- Replace By
- ASTM D6112-10
- Latest
- ASTM D6112-13
- Introduction
Standard Background and Development Purpose
ASTM D6112-23 "Standard Test Methods for Compressive and Flexural Creep and Creep Rupture of Plastic Wood and Profiles" was developed by the ASTM D20.20 Subcommittee, first published in 1997, with the latest revision in 2023. This standard targets plastic wood and profile products primarily made from recycled plastics, which are typically non-homogeneous in cross-section and unsuitable for evaluation using traditional material property test methods. The standard aims to measure creep deformation and time-to-rupture behavior by simulating constant loads under actual service conditions, providing long-term performance data for engineering design. Compared to traditional plastic creep test methods such as D2990, D6112 focuses more on the overall product performance rather than inherent material properties, and specifically specifies four-point bending loading and compressive loading methods.
Key Terms and Definitions
The standard clearly defines the following core terms: Plastic Wood refers to rectangular cross-section products made primarily from plastic (filled or unfilled), used for building applications similar to traditional wood; Plastic Profiles refers to similar products with non-rectangular cross-sections. In creep testing, Creep Strain refers to the total strain (elastic plus non-elastic) produced after applying stress, and Creep Modulus is the ratio of initial stress to the creep strain at that moment. Additionally, the standard distinguishes between Compressive Creep (shortening of length) and Flexural Creep (deflection at mid-span) deformation measurements. Understanding these terms is the foundation for correctly applying the standard.
Overview and Comparison of Test Methods
The standard covers two types of tests: compressive creep and flexural creep, both of which must be conducted under constant load and specified environmental conditions. Flexural creep uses four-point loading to measure mid-span deflection, while compressive creep uses parallel platens to measure changes in specimen height. Both require recording deformation-time curves and continuing until rupture or a predetermined time. The following table compares key elements of the two methods:
Test Type Specimen Shape Loading Method Measured Parameter Applicable Scenario Compressive Creep Right-angled prism, height is twice the minimum width Axial pressure applied by parallel platens Height change (compression amount) Simulating compression members such as columns and supports Flexural Creep Full-size profile, support span is 16 times the depth Four-point bending, load applied through cylindrical platen Mid-span deflection (measured from the bottom surface) Simulating bending members such as beams and plates Both methods require ensuring load accuracy of ±1%, deformation measurement accuracy of ±1%, temperature control within ±2°C, and humidity at 50±5%. The standard also emphasizes avoiding vibration and impact, and multi-station equipment must have designs that do not interfere with each other.
Equipment and Specimen Preparation Requirements
Regarding equipment, the Loading System and Deformation Measurement Device must be regularly calibrated and comply with the E4 procedure. Compressive creep requires self-aligning platens to ensure the load passes through the center of the specimen; flexural creep requires a rigid test frame with support and platen radii of at least 0.5 inches (12.7 mm), not exceeding 1.5 times the specimen depth. Specimens should be cut directly from "as-manufactured" products, maintaining the original surface, with only end faces machined to ensure parallelism. For hollow profiles, the specimen length must be at least twice the minimum cross-sectional dimension.
Test Condition Selection and Procedure
The standard recommends conducting tests at 23°C and 50% RH, but temperatures can be selected based on actual service environments (e.g., 10°C, 40°C). Creep testing requires at least three stress levels (for linear viscoelastic materials) or five (for non-linear materials); creep rupture testing requires at least seven stress levels, with target rupture times ranging from 1 hour to 3000 hours. The test procedure includes: installing the specimen, installing the deformation measurement device, rapidly applying load within 1-5 seconds, and recording deformation and environmental parameters according to a schedule (e.g., 1 minute, 6 minutes, etc.). For creep rupture, the rupture time or the start time of yielding must be recorded.
Calculations and Data Interpretation
When calculating, attention must be paid to dimensional changes caused by the environment, corrected using un-loaded control specimens. Compressive creep strain is obtained by dividing the compression amount by the initial gauge length; the maximum flexural creep strain is calculated using the formula (deflection × 4.7 × depth / span²), though the formula itself is not listed here. The creep modulus is the ratio of initial stress to strain. The standard also provides methods for plotting 1000-hour isochronous stress-strain curves and stress-rupture time regression curves to predict stress at 1% strain and long-term strength. The time-temperature superposition principle is recommended for constructing master curves to predict performance over extremely long durations.
Implementation Recommendations
When conducting D6112 tests, note the following: 1) Specimens should represent the final product, avoiding secondary processing that alters cross-sectional properties; 2) Ensure stable environmental control, especially temperature and humidity, as plastic wood is sensitive to heat and moisture; 3) For creep rupture tests, use protective nets or cushioning devices to prevent other specimens from being impacted; 4) If the material undergoes significant dimensional changes in the environment (e.g., post-curing shrinkage), control specimens must be used for correction; 5) Conduct rapid isochronous tests (e.g., 100h) before testing to verify that the equipment-specimen system is functioning normally. Data reports should include complete material information, test conditions, deformation-time curves, and regression parameters to support engineering design and product certification.
Technical Evolution and Application Prospects
With the widespread application of recycled plastics in the construction industry, D6112 has evolved from a single test method into a comprehensive system covering compression and bending, as well as creep and rupture. The 2023 revision focused on clarifying term definitions and supplementing details on four-point bending loading. In the future, with the popularity of composite plastic wood (such as wood-plastic composites), the standard may need to incorporate mixed-mode loading conditions. Currently, this standard has been used to evaluate the long-term load-bearing capacity of outdoor products such as docks, decks, and railings, providing critical data for structures with a design life of 25 years. Engineers can directly use creep modulus-time curves for deformation calculations under creep conditions, for example, by extrapolating after fitting with Norton's law (power law).
ASTM D6112-23 Referenced Document
- ASTM D2990 Standard Test Methods for Tensile, Compressive, and Flexural Creep and Creep-Rupture of Plastics
- ASTM D4000 Standard Classification System for Specifying Plastic Materials
- ASTM D5033 Standard Guide for Development of ASTM Standards Relating to Recycling and Use of Recycled Plastics *， 2026-07-13 Update
- ASTM D543 Standard Practices for Evaluating the Resistance of Plastics to Chemical Reagents
- ASTM D5947 Standard Test Methods for Physical Dimensions of Solid Plastics Specimens
- ASTM D883 Standard Terminology Relating to Plastics*， 2026-05-15 Update
- ASTM E176 Standard Terminology of Fire Standards
- ASTM E4 Standard Practices for Force Verification of Testing Machines
- ASTM E456 Standard Terminology for Relating to Quality and Statistics
ASTM D6112-23 history
- 2023 ASTM D6112-23 Standard Test Methods for Compressive and Flexural Creep and Creep-Rupture of Plastic Lumber and Shapes
- 2018 ASTM D6112-18 Standard Test Methods for Compressive and Flexural Creep and Creep-Rupture of Plastic Lumber and Shapes
- 2013 ASTM D6112-13 Standard Test Methods for Compressive and Flexural Creep and Creep-Rupture of Plastic Lumber and Shapes
- 2010 ASTM D6112-10 Standard Test Methods for Compressive and Flexural Creep and Creep-Rupture of Plastic Lumber and Shapes
- 1997 ASTM D6112-97(2005) Standard Test Methods for Compressive and Flexural Creep and Creep-Rupture of Plastic Lumber and Shapes
- 1997 ASTM D6112-97 Standard Test Methods for Compressive and Flexural Creep and Creep-Rupture of Plastic Lumber and Shapes
