Low velocity oblique impact behaviour of glass, carbon and aramid fibre reinforced polymer laminates

April 2025

Engineering researchers in the Faculty of Arts, Computing and Engineering, Dr Shafiul Monir, Professor Richard Day, Dr Nataliia Luhyna, Dr Martyn Jones and Dr Yuriy Vagapov, recently co-authored a paper on Low velocity oblique impact behaviour of glass, carbon and aramid fibre reinforced polymer laminates, with Dirk Banhart. The paper was published in the Mechanics of Advanced Materials and Structures journal.

The researchers undertook a numerical analysis of the performance of various composite laminates under low-velocity oblique impact to identify the damage thresholds of the laminates.

What is fibre reinforced polymer laminate?

Composite laminates are thin, strong, stiff, lightweight sheets made up of fibrous composite materials bound together. Fibre-reinforced polymer laminates are layers of polymer matrix, such as epoxy, bonded with reinforcing fibres, such as carbon, glass, or aramid.

The paper explains that Fibre-reinforced polymer laminates are increasingly used in high performance engineering sectors such as aerospace, automotive, and civil engineering. Use in these industries means that the composites can be subject to both low- and high-velocity impact hazards. Whilst high-velocity impacts often result in visible damage, low-velocity impacts can result in either clearly visible or barely visible impact damage, with the latter being the case more frequently. Barely visible impact damage can cause delamination, weakening the composite material and leaving it open to serious structural failure which can have very significant consequences. The researchers therefore set out to understand the performance of the materials under low velocity oblique impact, aiming to identify the realistic behaviours and fault prediction of composites that are subject to barely visible impact damage.

The approach taken

The standardised approach to investigating low-velocity impact is the drop-weight impact test, with supporting material behaviour and damage analysis. The authors detail that a lot of research in this field uses both experimental and numerical methods, with the practical being used to validate the numerical modelling. The work of Alomari et al, Gliszczynski and Gonzalez-Jimenez et al, amongst others, are cited as part of this discussion. An alternative to this method, which is more time and cost efficient, is numerical and analytical methods, without practical experiments and tests. Numerical and analytical methods offer great insight into material behaviour and a number of simulation-based research outputs and the findings are discussed within the paper.   

This study set out to analyse the low-velocity impact behaviour of Carbon fibre reinforced polymer (CFRP), glass fibre reinforced polymer (GFRP), and aramid fibre reinforced polymer (AFRP) laminate plates. The materials had “different quasi-isotropic and symmetric stacking sequences” and were “subjected to a range of oblique impacts”. The three composite materials were subject to the same numerical impact conditions to enable a comparative analysis. A novel element of this research was the use of ANSYS Composite PrepPostþTransient Structural, showcasing that the software is both “suitable and effective” for numerical impact research.

• A validation case was conducted to ensure the accuracy of the numerical simulation and this established a correlation of accuracy.
• Material strengths for the numerical analysis were taken from various published sources and used to calculate the composite laminates properties.
• A virtual model of the drop-weight impact test was created to analyse the impact performance from varying angles.
• A numerical validation case, assessing the correlation between experimental and numerical results, was undertaken.
• The virtual model was then used in a series of simulations to “investigate the influence of laminate stacking sequences on composite impact resistance under low-velocity oblique impacts at various impact angles”.
• The results were evaluated and compared, taking into account the type of composite material, the influence of stacking sequence on impact behaviour, and damage analysis.
• Recommendations for the design using composite laminates were then made.

In the world of fibre reinforced polymer matrix, the drop-weight impact test is used to test and measure resistance to damage and this was the basis for the impact performance investigation.

Figure 1. The drop-weight impact test set up (minus the four rubber pins which pressed the test specimen down onto the support)

Different impact velocities and angles of impact were used alongside the testing of six different stacking sequences for the composite laminate test specimen (listed in Table 2 in the paper). The selected stacking sequences are arranged in a way to provide “equal strength performance of the material in each direction of loading”, this enabled evaluation of how different fibre orientations “influence impact resistance and damage propagation”.

Process

Governing Equations

Detail of the governing equations are provided including the drop-weight test setup dimensions, calculations of the orthotropic material properties of unidirectional composite plies with different fibre reinforcements, and the applied Puck failure criterion.

Composite material properties

AGY E-glass fibre, Toray T700S carbon fibre, and Kevlar 49 aramid fibre were used in the investigation and TDE-307 85 with DDS curing agent epoxy resin was used as a matrix.

The paper details the properties of the unidirectional orthotropic composite ply material for GFRP, CFRP, and AFRP were calculated using the mixture rule and the Hashin relation. The ultimate strengths from several literature sources were collected and averaged, and these are presented within the paper.

The constants for GFRP, CFRP and AFRP were sourced from the literature and used to apply the Puck failure criterion.

Numerical FEM setup

The CAE software package ANSYS Workbench 2023 R1 Academic was used for simulation and details of the following are discussed within the paper:

• Utilised approach and software
• Mesh generation
• Simulation boundary conditions
• Validation case

Results and Discussion

A number of limitations of the numerical FEM investigations are detailed, including the restricted number of elements and nodes that may have affected accuracy.

Validation Case

The validation case demonstrated a strong correlation between the proposed numerical and experimental results. The delamination area measurements form part of the discussion, as this is the most relevant type of interlayer damage under low-velocity impact.

Stacking Sequences

The research showed that the highest performance was achieved by the stacking sequence QI-V for GFRP, by the stacking sequences QI-I, QI-IV, and QI-V for CFRP, and by the stacking sequences QI-IV and QI-V for AFRP. “The stacking sequences QI-II, and QI- VI performed poorly overall and are not recommended. In summary, the stacking sequence QI-V is a satisfactory compromise for GFRP, CFRP, and AFRP across the entire range of impact angles.”

Von Mises stress

The von Mises stress contours for the GFRP plies with specific stacking sequences are visually represented in terms of the 16 individual plies, demonstrating the differing stress patterns of each individual ply. The impact zones and distribution are considered, deducing that “it would be reasonable to replace only the outer plies with a higher-performing composite material” which enhances cost efficiency.

Figure 2. Top view von mises stress contours of GFRP plies with stacking sequence QI-V under 10J impact at the angle of 0˚ .

Kinetic energy and contact force

The kinetic energy decreases following impact on each of the three composite laminates were reviewed in detail, with material stiffness and stress distribution forming part of the outputs seen.

Deformation and Delamination

Deformation and delamination of the laminate plates and individual ply’s across GFRP, CFRP, and AFRP are reviewed in turn, with similarities between the materials being highlighted and key differences including stiffness being noted.

Conclusions

• Low-velocity impact up to an impact angle of 25˚ significantly increases the damage to the composite laminate plates.
• At angles over 25˚ the damage decreases rapidly. It then remains somewhat constant up to 55˚ and angles above this cause extensive damage.
• Across GFRP, CFRP, and AFRP the stacking sequence QI-V [0/45/−45/90/0/45/−45/90]s is the best compromise considering the full range of angles.
• For impact angles ranging from 0 ˚ to 25 ˚, QI-IV [45/−45/0/90/45/−45/0/ 90]s is optimal for CFRP and AFRP (excluding GFRP). From an impact angle of 30 ˚ onwards, the most appropriate stacking sequence is QI-III.

The authors conclude that “the highest von Mises stresses, which are more likely to cause damage, occur directly in the impact zone on the upper plies of the composite laminate plate. The next highest von Mises stresses are found in the lower plies, which are subjected to tension due to impact-induced deflection.” The lowest von Mises stresses are found in the middle of the composite laminate plates. It is therefore deemed reasonable to replace “only the outer plies with composite material exhibiting better performance characteristics, thereby creating a hybrid composite laminate plate”.

Trends identified in von Mises stresses across the varying stiffness of materials and the resulting delamination areas are analysed.

Recommendations for future research are made to further improve accuracy, including incorporating four rubber pins into the numerical drop-weight impact test setup and obtaining the material properties of GFRP, CFRP and AFRP through experimental testing rather than literature.

You can read the paper in full here.