|Book Review: SACMA Recommended Methods|
As anyone who has worked with composites knows, determining mechanical
properties and verifying material quality is a complex task. ASTM has
developed standards for many properties. Still, the set of standards
is not complete, and in some cases there is debate over the most
appropriate - or even the most accurate - test method.
To fill this gap, the Suppliers of Advanced Composite Materials
Association (SACMA) has issued its Recommended Methods
manual. This manual contains 27 composite test methods, covering
strength, stiffness and physical properties.
To fill this gap, the Suppliers of Advanced Composite Materials Association (SACMA) has issued its Recommended Methods manual. This manual contains 27 composite test methods, covering strength, stiffness and physical properties.
Each method is given an SRM designation (for SACMA Recommended Method), numbered 1 through 27. All methods were published in 1994, except for SRM 27-98, which was published in 1998. The methods can be broadly divided into two categories: mechanical testing of composites, and physical testing of material components.
The methods are divided into 12 sections and each follows a common format. The sections are: Scope; Reference Documents (including relevant ASTM standards); Summary of Method; Significance and Use; Interference (difficulties); Apparatus (with drawings); Test Specimen (geometry and layup, with drawings); Conditioning; Test Procedure; Validation; Calculation; and Report.
There is only a bit of overlap with ASTM standards. For example, SRM 1R-94, "Compressive Properties of Oriented Fiber-Resin Composites," is a version of ASTM D695, "Test Method for Compressive Properties of Rigid Plastics." The SRM method has been modified for reinforced plastics. There is no reference, though, to other common compressive test standards, such as ASTM D3410 (the IITRI test).
Those more familiar with international standards might find a little more overlap. For example, SRM 2-94 covers compression after impact (CAI) of composites. ASTM does not have any standards in this area, but CRAG (Composites Research Advisory Group) Method 403 is another CAI method. The SRM method uses a drop weight; the CRAG method uses a pendulum.
The bulk of the SRM methods cover physical property testing of material components. These methods are primarily intended for quality inspection during prepreg manufacture, or receiving inspection of materials prior to their use in manufacture. The physical property methods can be roughly grouped into two main categories: carbon tow characterization (mass per unit length, sizing content, twist, etc.); and prepreg characterization (glass transition temperature, fluid resistance, resin content, fiber/matrix adhesion, etc.).
The recommended methods are not true standards, but SACMA was coordinating with ASTM to obtain standards status on many of the methods. SACMA's responsibilities have been taken over by the Composites Fabricators Association (CFA), and it is not yet clear what the future development of these methods will be.
Details: SACMA Recommended Methods, by the Suppliers of Advanced Composite Materials Association, published by the Composites Fabricators Association (CFA), 1999.