Residual Strength Of Laminates Research Articles

Low-velocity impact and compression after impact behaviour of nanoparticles modified polymer composites

Optimizing the impact properties of polymer composites is essential in aircraft industries. Hybridization of fibres is one of the efficient methods to enhance the impact properties of polymer composites. Dispersion of nanoparticles into epoxy resin improves the toughness of composites. This study examines the low-velocity impact (LVI) behaviour of hybrid epoxy-based carbon/glass fibre-reinforced laminates. Initially, the epoxy resin was modified with 0, 0.5, 1, 1.5, and 2 wt% of nanoclay and TiO2 nanoparticles using mechanical stirring followed by an ultrasonication method. To investigate the influence of stacking sequences, laminates were fabricated with (90 G/0 G/90 C)S, (90 G/0 C/90 G)S, and (90 C/0 G/90 G)S. The samples used for this study are six-ply symmetric laminates. Laminates were impacted with different impact energies between 30 and 80 J with an impact velocity of 7 m/s to generate damages. The residual strength of damaged specimens is determined using compression after the impact test. The order of stacking, fibre orientation, and the presence of nanoparticles all have a significant impact on the residual strength of laminates. By using C-scan images, layer-wise damage mechanisms were identified. The specimen with (90 C/0 G/90 G)S sequence has very high damage resistance compared to other laminates.

Modelling damage evolution and CAI strength of composite laminates under biaxial compression

In this paper, a finite element model (FEM) was developed to investigate failure mechanism and compression after impact (CAI) strength of woven carbon fibre reinforced polymer (CFRP) after low-velocity impact (LVI) subjected to biaxial compressive loading. A built-in VUMAT user-defined material subroutine was adopted to take into account the in-plane damage and intralaminar delamination under LVI loading and in-plane compression. The LVI response, failure pattern, and residual mechanical properties under uniaxial compression were compared to the available experimental data to verify the numerical model. The damage initiation, subsequent evolution, final failure modes, and residual strength of the composite laminates with LVI damages subjected to biaxial compressive loading are presented by numerical methods, and the effects of impact energy and impactor diameter on the residual strength of the laminates are discussed.

Multi-level hybridization in mitigating impact damages in advanced composites – A review on recent trends

Advanced polymer laminated composites are widely used in various external structural components in modern aircraft and aerospace applications. These structures are vulnerable to different types of impact, more commonly low-velocity impact during its manufacturing, regular service, maintenance, and/or other phases of its life cycle. Impact damages produce a significant drop in the residual strength of laminates. These damages happen inside the core of the structure and are difficult to notice and repair. While considering the phenomenal increase in the application of polymer composites in aircraft and also the overall safety of the structure made out of them, it is imperative to find preventive solutions. A comprehensive review is presented in this article on various aspects of multi-level hybridization, especially in advanced fiber-reinforced polymer composites and strategies for the development of innovative hybrid composite materials to mitigate the damages caused in laminated composites as a result of low-velocity impacts. Hybridization strategy applied at fiber and matrix level for the enhancement of impact resistance through the improvement of in-plane and thru thickness properties are discussed along with the current efforts in making the damage detection easy and timely. An evaluation of recent developments for imparting impact performance in laminated composites used in external structures of aircraft and the future scope and trends in this field of research are presented.

Robust Empirical Predictions of Residual Performance of Damaged Composites with Quantified Uncertainties

Robust predictions with estimated uncertainties were made for the residual strength of impact-damaged composite laminates based on simple non-destructive measurements of the size of the damage from ultrasound C-scans. Experimental data was acquired for two sets of composite coupons, one with a crossply and the other with a quasi-isotropic layup. The laminates were subject to drop-weight impacts, non-destructively evaluated using ultrasound and then loaded to failure in bending. An empirical model of the residual strength of each laminate layup, as a function of the ultrasound measurements, was generated by fitting a Bayesian linear regression model to the normalised measured data. Bayesian linear regression was demonstrated to provide conservative estimates when only minimal data is available. Unlike classical regression, this technique provides a robust treatment of outliers, which avoids underestimation of residual strength. The Leave-One-Out-Cross-Validation (LOOCV) metric was used to assess the performance of models allowing for the quantitative comparison of the predictive power of regression models as well as being consistent in the presence of outliers in the data. The LOOCV metric indicated that predictions of residual strength are up to 25% more accurate when based on damage area than when using measurements of the damage width or length. The proposed approach provides a robust methodology for performing damage assessments in safety critical composite components based on reliable predictions with quantified uncertainties.

Experimental and Numerical Investigation on the Residual Strength of Laminates with Central and Edge Notch

Abstract: In this paper, experimental and finite element methods are integrated to carry out the research about residual strength of composite laminate structure with central and edge notch. First, the specimens with central and edge notch and the fixtures used in compression tests were designed and manufactured, and the tensile and compression residual strengths with different notch size were measured. Then, finite element analysis model of specimens with central and edge notch were established to predict the residual strength based on the average stress criterion and Hoffman criterion, the effect of the notch size on the residual strength is evaluated, the results were compared and found that the average stress model has higher prediction accuracy and notch size has a significant influence on the residual strength of composite laminate structure with central and edge notch.

Estimation of residual flexural strength of unidirectional glass fiber reinforced plastic composite laminates under repeated impact load

The aim of this study is to investigate the effect of low-velocity multiple impacts at ambient (35℃) and elevated temperature (65℃ and 85℃) on unidirectional glass fiber reinforced plastic (GFRP) composites. Low-velocity repeated impact tests were conducted using a falling weight tower at a constant velocity of 1.5 m/s. The dominant parameters such as energy, contact force, and deflection were recorded during multiple impacts. The residual strength of laminates following repeated impact was evaluated by conducting three-point bending tests with acoustic emission (AE) real time monitoring. The temperature was revealed to play a key role in the impact response of composite materials, especially due to the progressive softening of the epoxy matrix. The nature and extent of damage during multiple impacts at ambient and elevated temperatures was investigated using real time AE monitoring: this analysis indicated delamination as a predominant failure mode, whose extent and criticality depended on temperature and number of impact events.

Study of fiber hoop-wrapped composite cylinders impact resistance

The composite/metal hybrid structure, which has different impact damage characteristics compared with conventional composite structure, is widely used in composite Compressed Natural Gas (CNG) cylinders of new energy vehicles. This paper, combining both the tests of composite cylinder and specimen, evaluates cylinder’s impact resistance performance with parameters such as: impact energy absorption rate, delamination extension resistance and attenuation factor of the residual strength ratio.It is found that, under certain impact energy, changing composite/metal hybrid structure leads to the change of impact energy absorption rate and increases impact damage critical value, namely, load bearing capacity. Higher impact energy absorption rate will reduce delamination extension resistance, and the residual strength of laminates with impact damage will attenuate faster. As a result, the effect of delamination extension resistance and impact energy absorption rate should be taken into consideration while designing composite cylinders.

Residual Tensile Strength Prediction on a Ply-by-Ply Basis for Laminates Containing Impact Damage

Impact loading on composite laminates can cause surface or internal damage in the form of fiber breakage, delamination and matrix cracking. Such damage can reduce laminate tensile strength. In the work presented here, impact damage was modelled as part through-the-thickness damage and laminate residual strength was evaluated by ex amining the behavior of each individual ply of the laminate. A residual strength prediction procedure, proposed previously for laminates containing cut internal fibers, was used here for laminates containing impact damage. The prediction of laminate residual strength was performed based on 3-D finite element results in conjunction with a principal load carry ing ply failure criterion. The predicted residual strength agreed with the experimental data within the bounds of 0.85 to 1.08 times the experimental data, indicating the applicability of the procedure and the damage modelling technique.