Damage Development In Composite Laminates Research Articles

Computational Modeling of Damage Development in Composite Laminates Subjected to Transverse Dynamic Loading

This paper presents a robust computational model for the response of composite laminates to high intensity transverse dynamic loading emanating from local impact by a projectile and distributed pressure pulse due to a blast. Delaminations are modeled using a cohesive type tie-break interface introduced between sublaminates while intralaminar damage mechanisms within the sublaminates are captured in a smeared manner using a strain-softening plastic-damage model. In the latter case, a nonlocal regularization scheme is used to address the spurious mesh dependency and mesh-orientation problems that occur with all local strain-softening type constitutive models. The results for the predicted damage patterns using the nonlocal approach are encouraging and qualitatively agree with the experimental observations. The predictive performance of the proposed numerical model is assessed through comparisons with available instrumented impact test results on a class of carbon-fiber reinforced polymer (CFRP) composite laminates. Force-time histories and other derived cross-plots such as the force versus projectile displacement and progression of projectile energy loss as a function of time are compared with available experimental results to demonstrate the efficacy of the model in capturing the details of the dynamic response. Another case study involving the blast loading of CFRP composite laminates is used to further highlight the capability of the proposed model in simulating the global structural response of composite laminates subjected to distributed pressure pulses.

Broad-band transient recording and characterization of acoustic emission events in composite laminates

Acoustic emission (AE) transients due to different kinds of microdamage, such as matrix cracking, fiber breakage and local delaminations, have been recorded in glass/epoxy composite laminates. Different stacking sequences, [0°, 90° 2] S , [90° 2, 0°] S , [+45°, −45°] S and [0° 4], were used in order to trigger different crack mechanisms during tensile testing. The AE transients were recorded as functions of time by the use of broad-band AE transducers. In the experiments, it was observed that different types of cracks generated acoustic emission signals varying in amplitude, duration time and frequency content. It was also seen that the same type of crack produced signals with different characteristics depending on the layer in which the crack appeared and its orientation compared to the location of the transducer. The majority of signals from the tests could be divided into a few main groups. Typical signals and characteristics representing these groups are presented in the paper. The observations show that there is a potential in future development of quantitative methods for identification of damage development in composite laminates.

Damage accumulation in woven-fabric CFRP laminates under tensile loading: Part 1. Observations of damage accumulation

Damage development in composite laminates reinforced with two-, four- and six-layer carbon-fibre-reinforced polyimide eight-harness satin-weave fabric has been observed as a function of applied strain. Residual properties (Young’s modulus, Poisson’s ratio and residual strain), together with damage accumulation, have been recorded as a function of applied strain. Distinct differences which emerge in the behavior of the residual properties of the laminates with increasing applied strain are related to the different types of damage which accumulate in the laminates.

Kinematic Waves and Nonuniform Damage Development in Composite Laminates

When subjected to fatigue loading, the off-axis plies of some polymer matrix laminates undergo a transverse cracking whose density is maximum close to the free edges and decreases toward the specimen center; moreover, this damage distribution evolves as the number of cycles increases. The "kinematic wave" concept is applied to the principle of conservation of number of crack tips, along with suitable assumptions concerning the velocity of a crack tip propagating into a material whose damage state is characterized by a local crack density. This principle gives a nonlinear wave equation governing damage as a function of both distance x from a free edge and number N of cycles. Experimental results pertaining to a cross-ply carbon/epoxy laminate whose 90° layers are thin compared to the longitudinal layers are obtained in the form of successive X-ray pictures taken at different times in the specimen life. Plotting the contour lines of damage in the (x,N) plane results in a family of straight lines which can be interpreted as the characteristic curves of a simple wave solution for the above wave equation. Measuring the slope of each curve of this family, along which damage is constant, allows the coefficient of the wave equation to be determined as a function of damage. A power law is found to fit well with the corresponding curve, which assesses the consistency of the model with the experimental results for the laminate investigated. The damage growth law obtained in this manner is the first step toward the future construction of a more general model which could be used to predict the service life of a composite structural part.

Damage development in composite laminates with brittle matrix in fatigue loading

This Paper presents a study on damage development in composite laminates. Damage propagation in dry carbon fibre reinforced polyimides is reported for fatigue loading. General information is also given on the fatigue behaviour of other matrix materials at low temperatures.

Engineering Life Prediction of Composite Materials: Elements of a Mechanistic Model

It is the practice in engineering to attempt to avoid problems that we do not understand; such is frequently the case for damage development in composite materials. The prudent designer prescribes design strain levels low enough so that damage development is thought to be precluded. However, something should be known of damage development if it is to be avoided, and the basic question of how long a particular structure will last cannot be answered without some understanding of damage development in composite materials. As new material systems and applications are developed and as old ones are further exploited, a more and more precise understanding of damage development will be required. What is needed is a rational analysis that can be used to describe and explain damage development in composite laminates so that we can anticipate their residual strength, stiffness, and life under engineering conditions. In general, this requires a replacement for the single-crack problem (and fracture mechanics) in homogeneous isotropic materials.