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Significance and Use
Susceptibility to damage from concentrated out-of-plane impact forces is one of the major design concerns of many structures made of advanced composite laminates. Knowledge of the damage resistance properties of a laminated composite plate is useful for product development and material selection.
Drop-weight impact testing can serve the following purposes:
To establish quantitatively the effects of stacking sequence, fiber surface treatment, variations in fiber volume fraction, and processing and environmental variables on the damage resistance of a particular composite laminate to a concentrated drop-weight impact force or energy.
To compare quantitatively the relative values of the damage resistance parameters for composite materials with different constituents. The damage response parameters can include dent depth, damage dimensions, and through-thickness locations, F1, Fmax, E1 and Emax, as well as the force versus time curve.
To impart damage in a specimen for subsequent damage tolerance tests, such as Test Method D7137/D7137M.
The properties obtained using this test method can provide guidance in regard to the anticipated damage resistance capability of composite structures of similar material, thickness, stacking sequence, and so forth. However, it must be understood that the damage resistance of a composite structure is highly dependent upon several factors including geometry, thickness, stiffness, mass, support conditions, and so forth. Significant differences in the relationships between impact force/energy and the resultant damage state can result due to differences in these parameters. For example, properties obtained using this test method would more likely reflect the damage resistance characteristics of an unstiffened monolithic skin or web than that of a skin attached to substructure which resists out-of-plane deformation. Similarly, test specimen properties would be expected to be similar to those of a panel with equivalent length and width dimensions, in comparison to those of a panel significantly larger than the test specimen, which tends to divert a greater proportion of the impact energy into elastic deformation.
The standard impactor geometry has a blunt, hemispherical striker tip. Historically, for the standard laminate configuration and impact energy, this impactor geometry has generated a larger amount of internal damage for a given amount of external damage, when compared with that observed for similar impacts using sharp striker tips. Alternative impactors may be appropriate depending upon the damage resistance characteristics being examined. For example, the use of sharp striker tip geometries may be appropriate for certain damage visibility and penetration resistance assessments.
The standard test utilizes a constant impact energy normalized by specimen thickness, as defined in 11.7.1. Some testing organizations may desire to use this test method in conjunction with D7137/D7137M to assess the compressive residual strength of specimens containing a specific damage state, such as a defined dent depth, damage geometry, and so forth. In this case, the testing organization should subject several specimens, or a large panel, to multiple low velocity impacts at various impact energy levels using this test method. A relationship between impact energy and the desired damage parameter can then be developed. Subsequent drop weight impact and compressive residual strength tests can then be performed using specimens impacted at an interpolated energy level that is expected to produce the desired damage state.
1.1 This test method determines the damage resistance of multidirectional polymer matrix composite laminated plates subjected to a drop-weight impact event. The composite material forms are limited to continuous-fiber reinforced polymer matrix composites, with the range of acceptable test laminates and thicknesses defined in 8.2.
1.1.1 Instructions for modifying these procedures to determine damage resistance properties of sandwich constructions are provided in Practice D7766/D7766M.
1.2 A flat, rectangular composite plate is subjected to an out-of-plane, concentrated impact using a drop-weight device with a hemispherical impactor. The potential energy of the drop-weight, as defined by the mass and drop height of the impactor, is specified prior to test. Equipment and procedures are provided for optional measurement of contact force and velocity during the impact event. The damage resistance is quantified in terms of the resulting size and type of damage in the specimen.
1.3 The test method may be used to screen materials for damage resistance, or to inflict damage into a specimen for subsequent damage tolerance testing. When the impacted plate is tested in accordance with Test Method D7137/D7137M, the overall test sequence is commonly referred to as the Compression After Impact (CAI) method. Quasi-static indentation per Test Method D6264/D6264M may be used as an alternate method of creating damage from an out-of-plane force and measuring damage resistance properties.
1.4 The damage resistance properties generated by this test method are highly dependent upon several factors, which include specimen geometry, layup, impactor geometry, impactor mass, impact force, impact energy, and boundary conditions. Thus, results are generally not scalable to other configurations, and are particular to the combination of geometric and physical conditions tested.
1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.5.1 Within the text the inch-pound units are shown in brackets.
1.6 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 health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D792 Test Methods for Density and Specific Gravity (Relative Density) of Plastics by Displacement
D883 Terminology Relating to Plastics
D3763 Test Method for High Speed Puncture Properties of Plastics Using Load and Displacement Sensors
D3771 Specification for Rubber Seals Used in Concentrating Solar Collectors
D3878 Terminology for Composite Materials
D5229/D5229M Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite Materials
D5678 Test Method for Freeze/Thaw Resistance of Wax Emulsion Floor Polish
D6264/D6264M Test Method for Measuring the Damage Resistance of a Fiber-Reinforced Polymer-Matrix Composite to a Concentrated Quasi-Static Indentation Force
D7137/D7137M Test Method for Compressive Residual Strength Properties of Damaged Polymer Matrix Composite Plates
D7766/D7766M Practice for Damage Resistance Testing of Sandwich Constructions
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E18 Test Methods for Rockwell Hardness of Metallic Materials
E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E456 Terminology Relating to Quality and Statistics
E1309 Guide for Identification of Fiber-Reinforced Polymer-Matrix Composite Materials in Databases
E1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases
E2533 Guide for Nondestructive Testing of Polymer Matrix Composites Used in Aerospace Applications
ICS Number Code 83.120 (Reinforced plastics)