A number in parentheses indicates the year of last reapproval. Asuperscript epsilon indicates an editorial change since the last revision or reapproval. This limited scope reflects the experience gained inround-robin testing. This test method may prove useful forother types and classes of composite materials; however,certain interferences have been noted see 6.
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A number in parentheses indicates the year of last reapproval. Asuperscript epsilon indicates an editorial change since the last revision or reapproval. This limited scope reflects the experience gained inround-robin testing. This test method may prove useful forother types and classes of composite materials; however,certain interferences have been noted see 6. The values given in parentheses are for informationonly.
It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. Referenced Documents2. Terminology D de-fines terms relating to plastics. Terminology E6 defines termsrelating to mechanical testing. Terminology E and PracticeE define terms relating to statistics. In the event of conflictbetween terms, Terminology D shall have precedenceover the other terminology standards.
NOTE 1If the term represents a physical quantity, its analyticaldimensions are stated immediately following the term or letter symbol infundamental dimension form, using the following ASTM standard sym-bology for fundamental dimensions, shown within square brackets [M]for mass, [L] for length, [T] for time, [u] for thermodynamic temperature,and [nd] for non-dimensional quantities.
Use of these symbols is restrictedto analytical dimensions when used with square brackets, as the symbolsmay have other definitions when used without the brackets. Current edition approved Oct. Published November Originallyapproved in DOI United States In mathematical form,G bdUda1whereU total elastic energy in the test specimen,b specimen width, anda delamination length.
CV coefficient of variation,. E11 modulus of elasticity in the fiber direction. E1f modulus of elasticity in the fiber direction measured inflexure. F large displacement correction factor. G strain energy release rate. GIc opening Mode I interlaminar fracture toughness. L length of DCB specimen. L half width of loading block. N loading block correction factor. NL point at which the load versus opening displacementcurve becomes nonlinear. P applied load. Pmax maximum applied load during DCB test.
SD standard deviation. U strain energy. VIS point at which delamination is observed visually onspecimen edge. Vf fiber volume fraction,. Summary of Test Method4. Opening forces are applied tothe DCB specimen by means of hinges Fig. The endsof the DCB are opened by controlling either the openingdisplacement or the crosshead movement, while the load anddelamination length are recorded.
Instanta-neous delamination front locations are marked on the chart atintervals of delamination growth. The Mode I interlaminarfracture toughness is calculated using a modified beam theoryor compliance calibration method. Significance and Use5. Furthermore, a measurement of the Mode Iinterlaminar fracture toughness, independent of specimen ge-ometry or method of load introduction, is useful for establish-ing design allowables used in damage tolerance analyses ofcomposite structures made from these materials.
This assumption is valid when thezone of damage or nonlinear deformation at the delaminationfront, or both, is small relative to the smallest specimendimension, which is typically the specimen thickness for theDCB test.
In this test method,a resistance curve R curve depicting GIcas a function ofdelamination length will be generated to characterize thea with piano hinges b with loading blocksFIG. The principal reason for the observedresistance to delamination is the development of fiber bridging Becausemost delaminations that form in multiply laminated compositestructures occur between plies of dissimilar orientation, fiberbridging does not occur. Hence, fiber bridging is considered tobe an artifact of the DCB test on unidirectional materials.
Therefore, the generic significance of GIcpropagation valuescalculated beyond the end of the implanted insert isquestionable, and an initiation value of GIcmeasured from theimplanted insert is preferred.
Because of the significance of theinitiation point, the insert must be properly implanted andinspected 8. These include GIcvalues determined using the load and deflection measured 1at the point of deviation from linearity in the load-displacementcurve NL, 2 at the point at which delamination is visuallyobserved on the edge VIS measured with a microscope asspecified in 7.
The NL GIcvalue, which istypically the lowest of the three GIcinitiation values, isrecommended for generating delamination failure criteria indurability and damage tolerance analyses of laminated com-posite structures 5. Recommendations for obtaining theNL point are given in AnnexA2. All three initiation values canbe used for the other purposes cited in the scope 5. However, physical evidence indicates that the initiationvalue corresponding to the onset of nonlinearity NL in theload versus opening displacement plot corresponds to thephysical onset of delamination from the insert in the interior ofthe specimen width 5.
Only thefirst type of growth is of interest in this test method. Anunstable jump from the insert may be an indication of aproblem with the insert. For example, the insert may not becompletely disbonded from the laminate, or may be too thick,resulting in a large neat resin pocket, or may contain a tear orfold. Furthermore, rapid delamination growth may introducedynamic effects in both the test specimen and in the fracturemorphology.
Treatment and interpretation of these effects isbeyond the scope of this test method. However, because crackjumping has been observed in at least one material in which theguidelines for inserts see 8. Brittle matrix composites with tough adhesiveinterleaves between plies may be particularly sensitive to thisphenomenon resulting in two apparent interlaminar fracturetoughness values one associated with a cohesive-type failurewithin the interleaf and one associated with an adhesive-typefailure between the tough polymer film and the more brittlecomposite matrix.
If the delaminationbranches away from the midplane, a pure Mode I fracture maynot be achieved as a result of the structural coupling that mayexist in the asymmetric sublaminates formed as the delamina-tion grows. In addition, nonunidirectional specimens mayexperience significant anticlastic bending effects that result innonuniform delamination growth along the specimen width,particularly affecting the observed initiation values.
Composites with significant strength ortoughness through the laminate thickness, such as compositeswith metal matrices or 3D fiber reinforcement, may experiencefailures of the beam arms rather than the intended interlaminarfailures. The testing machine shallconform to the requirements of Practices E4.
The testing3The boldface numbers in parentheses refer to the list of references at the end ofthis test method.
ASTM D5528 PDF
The sample used is a double cantilever beam DCB specimen, which is a rectangular, unidirectional laminated composite specimen containing a nonadhesive film on the midplane that serves as a delamination initiator. Susceptibility to delamination is one of the major weaknesses of advanced laminated composites due to their structure. Mode I interlaminar fracture toughness measures the critical value of delamination growth as a result of an opening load. It is used to establish the design allowables used in damage analyses of composite structures. Delamination growth is characterized by strain energy release rate and the way the load is applied opening or tensile load per Mode I. The standard specimen length is at least mm 5.
ASTM D5528 Composite Fracture Toughness Testing
Nikozragore Sales Support Calibration Calculators. Start recording the delamination length on one side of the specimen from the marks and record the data astm d on the load-displacement curve when visual onset of delamination is observed. This test apparatus is useful to determine the opening Mode I interlaminar fracture toughness, G Icof continuous fiber-reinforced composite materials by astm d double cantilever beam specimen. Sum of distance from the loading line to the end of the insert plus the increment growth determined from the astm d Mark the position of the tip of the precrack on axtm edges. There astm d three methods to calculate the interlaminar astm d toughness: This test application is employable with astm d consisting of unidirectional carbon fiber and glass fiber tape laminates with brittle and tough single-phase polymer matrices.