Prediction Of Impact Damage Research Articles

The discrete element method (DEM) to simulate fruit impact damage during transport and handling: Model building and validation of DEM to predict bruise damage of apples

The validity of the discrete element method (DEM) as a tool to predict impact damage of fruit was investigated for ‘Jonagold’ apples. ‘Bruise damage’ was preferred over the ‘particle trajectory’ as the validation parameter. The bruise damage of apples in boxes shaken with a well defined acceleration signal on an electro-hydraulic shaker was compared with the bruise damage calculated from DEM simulations with the same initial conditions. The parameters for the contact force models, needed as input for the simulations, and the bruise prediction model were determined on the same batch of apples, utilized in the validation experiments. The validations indicated that DEM can predict in an acceptable way apple bruise damage (bruise depth). However, due to the lack of the possibility of saving the impact positions on the apple surface by means of a coordinate system no prediction of multi-impact bruise surface and volume could be obtained.

06/01045 Energy efficiency and energy savings in Japanese residential buildings - research methodology and surveyed results: Lopes, L. et al. Energy and Buildings, 2005, 37, (7), 698–706.

The validity of the discrete element method (DEM) as a tool to predict impact damage of fruit was investigated for ‘Jonagold’ apples. ‘Bruise damage’ was preferred over the ‘particle trajectory’ as the validation parameter. The bruise damage of apples in boxes shaken with a well defined acceleration signal on an electro-hydraulic shaker was compared with the bruise damage calculated from DEM simulations with the same initial conditions. The parameters for the contact force models, needed as input for the simulations, and the bruise prediction model were determined on the same batch of apples, utilized in the validation experiments. The validations indicated that DEM can predict in an acceptable way apple bruise damage (bruise depth). However, due to the lack of the possibility of saving the impact positions on the apple surface by means of a coordinate system no prediction of multi-impact bruise surface and volume could be obtained.

Post-impact flexural tests on jute/polyester laminates monitored by acoustic emission

A number of industrial sectors, including automotive, building and leisure, have recently shown interest on natural fibers, as reinforcement for low-weight, environmental-friendly materials. The introduction of natural fiber composites in components for large volume applications requires studies aimed at predicting their in-service behavior, in particular fatigue and impact testing. Some recent investigations have raised concerns on the performance of these materials, especially when subjected to a high number of cycles, as an effect of a long-service life, in harsh environmental conditions [1‐3]. The use of nondestructive testing techniques, such as acoustic emission, as monitoring methods during mechanical tests, proved useful in previous studies on mechanical characterization of natural fiber composites [4, 5]. Two approaches are used to predict impact damage on laminated composites reinforced with artificial fibers [6]. The first one is based on estimating the overall size of impact-damaged area and considering stress distribution in the region surrounding the impact point, whilst the second one is aimed at detecting the appearance of the first matrix crack, then the study of the initiation and propagation of delamination. When dealing with plant-fiber composites, both approaches are viable, at least in principle: however, a number of difficulties can be perceived. First, the measurement of impact-damaged area has been revealed to be particularly difficult, as an effect of the fibers becoming loose and suffering early debonding around the impact point, even at low stress [7]. Second, the study of impact damage initiation is based on the assumption that the laminate shows limited presence of defects prior to impact and that the direction of impact, whether mono- or bi-dimensional, determines the damage propagation mode. However, in biological materials, such as plant fibers, the combined presence of stronger and weaker parts is a natural layout, aimed at obtaining the maximum possible impact resistance. In other words, natural materials work effectively through the limited and controlled occurrence of defects [8]. In plant fiber reinforced composites, because of the larger dimensional variability of fibers and fiber bundles, defects can more easily lead to disruptions in the laminate geometry than in glass fiber reinforced composites [9]. In addition, the capability of detecting defects and especially measuring their level of criticality is crucial to arrive to the possible production of components with plant fibers reinforcement. In this context, the acoustic emission (AE) technique can present some interest, for its capability of providing data from real-time monitoring during post-impact testing [10]. In the present work, plain woven jute fabric/polyester plates (100 mm×100 mm), manufactured using a resin transfer moulding (RTM) process with a 60% wt. reinforcement content, have been impacted and then subjected to cyclic post-impact three-point bending tests. The impact energy was changed, by varying the mass of the hemispherical drop-weight steel impactor, whilst maintaining the impact velocity constant at 2 m/s (±5%). Impact tests were conducted on a CEAST Fractovis impact tower fitted with an anti-rebound device. The plates were divided into eight categories with five specimens in each category. One group of specimen was not impacted, while the remainder were impacted at energies of 5, 7.5, 10, 12.5, 15 and 20 J, and the last one was impacted to penetration according to ASTM D3763, always using a hemispherical impactor tip diameter 12.7 mm. Depending on the impact energy, the total mass of the impactor varied: 2.53 kg (5 J), 3.89 kg (7.5 J), 4.99 kg (10 J), 6.26 kg (12.5 J), 7.54 kg (15 J), and 9.97 kg (20 J). The penetration energy measured on these laminates was equal to 25 (±2.2) J. On the impacted specimens, a 25.4 mm diameter indentor was used to undertake cyclic three-point bend tests, using an Instron 9400 universal testing machine, and following the scheme in Fig. 1. A loading rate of 4 mm/min was used. This condition was the

Prediction of impact damage on sandwich composite panels

Sandwich structures are extensively employed in the aerospace and automobile industries. The understanding of their behaviour under impact conditions is extremely important for the design and manufacturing of these engineering structures since impact problems are directly related to structural integrity and safety requirements. This paper investigates the damage behaviour of composite sandwich panels with aramid paper honeycomb (NOMEX) and polyetherimide (PEI) foam cores under transverse impacts at high velocities. A numerical model was developed using the dynamic explicit finite element (FE) structure analysis program PAM-CRASH. For both sandwich structures numerical analysis reproduces physical behaviour observed experimentally in high velocity impact tests.

Modelling soft body impact on composite structures

The paper describes recent progress on materials modelling and numerical simulation of soft body impact damage in fibre reinforced composite structures. The work is based on the application of finite element (FE) analysis codes to simulate composite shell structures under impact loads arising, for example, from bird strike on a wing leading edge. A composites ply damage mechanics model and interply delamination model have been implemented in an explicit FE code which is used to predict impact damage in shell structures. Soft body impactors such as gelatine (substitute bird) or ice (hailstones) are highly deformable on impact and flow over the structure spreading the impact load. They are modelled by a particle method in which the FE mesh is replaced by interacting particles. The failure models and code developments are applied to the numerical simulation of gas gun impact tests in which gelatine projectiles are fired at glass fabric/epoxy cylindrical shells.

Numerical simulations of low-velocity impact on an aircraft sandwich panel

The potential hazards resulting from a low-velocity impact (bird-strike, tool drop, runway debris, etc.) on aircraft structures, such as engine nacelle or a leading edge, has been a long-term concern to the aircraft industry. Certification authorities require that exposed aircraft components must be tested to prove their capability to withstand low-velocity impact without suffering critical damage. This paper describes the results from experimental and numerical simulation studies on the impact and penetration damage of a sandwich panel by a solid, round-shaped impactor. The main aim was to prove that a correct mathematical model can yield significant information for the designer to understand the mechanism involved in the low-velocity impact event, prior to conducting tests, and therefore to design an impact-resistant aircraft structure. Part of this work presented is focused on the recent progress on the materials modelling and numerical simulation of low-velocity impact response onto a composite aircraft sandwich panel. It is based on the application of explicit finite element (FE) analysis codes to study aircraft sandwich structures behaviour under low-velocity impact conditions. Good agreement was obtained between numerical and experimental results, in particular, the numerical simulation was able to predict impact damage and impact energy absorbed by the structure.

Prediction of low velocity impact damage in carbon–epoxy laminates

It is well known that composite laminates are easily damaged by low velocity impact. This event causes internal delaminations that can drastically reduce the compressive strength of laminates. In this study, numerical and experimental analyses for predicting the damage in carbon–epoxy laminates, subjected to low velocity impact, were performed. Two different laminates (04,904)s and (02,±452,902)s were tested using a drop weight testing machine. Damage characterisation was carried out using X-rays radiography and the deply technique. The developed numerical model is based on a special shell finite element that guarantees interlaminar shear stresses continuity between different oriented layers, which was considered fundamental to predict delaminations. In order to predict the occurrence of matrix failure and the delaminated areas, a new failure criterion based on experimental observations and on other developed criteria, is included. A good agreement between experimental and numerical analysis for shape and orientation of delaminations was obtained. For delaminated areas, reasonable agreement was obtained.

Engineering Method for Prediction of Impact Response and Damage in Sandwich Panels

An engineering method is suggested for prediction of impact response and damage of flat sandwich panels. The approach accounts for local core crushing, delamination and large face sheet deflections and does not rely on empirical indentation laws. Different models are suggested depending upon the impactor mass being either larger or significantly smaller than the mass of the impacted panel. The solution for large mass impact is based on closed form expressions. The solution for small mass impact is obtained from a dimensionless two-parameter integral equation. The validity of the approach is demonstrated on a number of static indentation experiments and impacts on sandwich panels.

Computational methods for predicting impact damage in composite structures

This paper describes recent progress in materials modelling and numerical simulation of the impact response of fibre-reinforced composite structures. A continuum damage-mechanics (CDM) model for fabric-reinforced composites is developed as a framework within which both in-ply and delamination failure may be modelled during impact loading. Damage-development equations are derived and appropriate materials parameters determined from experiments. The CDM model for in-plane failure has been implemented in a commercial explicit finite element (FE) code, and new techniques are used to model the laminate as a stack of shell elements tied by contact interface conditions. This approach allows the interlaminar layers to be modelled and strength reduction due to delamination to be represented; it also provides a computationally efficient method for the analysis of large-scale structural parts. The code is applied to predict the response of carbon-fabric-reinforced epoxy plates impacted at different velocities by a steel impactor. A comparison of structural response and failure modes from numerical simulations and impact tests is given which shows a good agreement for the prediction of delamination damage at low impact energies and fracture and penetration at higher impact energies.

A delamination criterion for laminated composites under low-velocity impact

This paper describes details of an improved delamination criterion for laminated composite structures and its implementation to LS-DYNA3D. Out-of-plane stresses have been taken into consideration for damage initiation. The new delamination criterion, verified by experimental results for low-velocity impact, takes into consideration both the interlaminar shear and through-thickness compression stresses. Improved from the criterion proposed previously [Hou JP, Petrinic N, Ruiz C. Prediction of impact damage in composite plates. Composites Science and Technology 2000; 60(2): 273–81], delamination is not fully constrained by the out-of-plane compression. The influences of high local interlaminar shear stress induced by matrix cracking and fibre failure on delamination have also been taken into account. Predicted results from different criteria have been discussed, in comparison with experiment work.

Analytical prediction of large mass impact damage in composite laminates

Analytical models are suggested for prediction of impact damage initiation and growth during quasi-static response caused by large mass impactors. Comparisons with experiments are presented for different layups, geometries and boundary conditions. The critical load for delamination growth is found almost insensitive to geometry and boundary conditions. The critical energy for delamination growth is separated in bending, shear and indentation contributions. Further growth depends on the number of delaminations developing, and is in thin laminates limited by the early occurrence of penetration. Observed delamination sizes are compared with a suggested upper bound and predictions based on the observed number of delaminations.

Modeling Hail Ice Impacts and Predicting Impact Damage Initiation in Composite Structures

Hail ice impacts are a realistic threat to exposed composite structures such as aircraft fuselage and wing skins, leading-edgeandcontrolsurfaces,enginenacelles,andfanblades.Toshedsomelightontothislittle-understood (and unavoidable ) threat, experimental, numerical, and analytical investigations have been conducted. Experiments in whichcarbon/epoxy compositepanelswereimpacted by icespheresathigh velocity (30‐200m/s)wereconducted to measure 1)the impact energy at which damage initiates, 2 ) the multiple failure modes exhibited by thin composite panels over a range of impact velocity, and 3 ) the elastic response of a composite panel resulting from impact. Subsequent numerical analyses of the last case were performed and were validated through correlation with experimental data. Insights gained from the numerical analyses were used to compose a mechanics-based formula that predicts the initiation of damage formation. This formula, derived using a global energy balance, provides a cost-effective (i.e., lower number of tests needed ) means by which the impact damage resistance of composite structures and material types can be established.

Predicting impact damage of composite stiffened panels

AbstractThis paper addresses the problem of the complex nature of low velocity impact damage in fabricated structures made of laminated carbon-epoxy composites. The structures chosen are stiffened compression panels since these are the most vulnerable to delamination and debonding. Four ‘top-hat’ stiffened panels were tested and predicted using a dynamic finite element code. The panels all had considerable postbuckling strength so the impact sites were carefully chosen to inflict maximum loss of strength. It was shown that the threshold energy for onset of delamination can be predicted using a dynamic finite element code. The amount of delamination or debonding is also predicted using a crude strength-based criterion, which seems to work only because the maximum impact force is a transient phenomenon of short duration.

Prediction of impact damage in composite plates

This paper gives details of the implementation of improved failure criteria for laminated composite structures into LS-DYNA3D. Out-of-plane stresses have been taken into consideration for damage initiation. It is suggested, for the first time, that delamination is constrained by through-thickness compression stress. Interactions between different damage mechanisms have been considered. Damage predictions in good agreement with experimental ones have been achieved.

Modeling hail ice impacts and predicting impact damage initiation in composite structures

Modeling hail ice impacts and predicting impact damage initiation in composite structures

Impact damage prediction and failure analysis of heavily loaded, blade-stiffened composite wing panels

Within the framework of a European research programme to develop design methodology for the improvement of damage tolerance within composite materials, two heavily loaded, stiffened composite wing panels were designed, fabricated and tested. The panels were impacted at the vulnerable stiffener edges and the failure modes and mechanisms related to the infliction of impact damage and the subsequent compression after impact loading were determined. A capability to predict the occurrence of impact damage by finite element analysis was demonstrated and guidelines for the design of damage tolerant panels were established. The laminate composition of two panel skins was quasi-isotropic. The test results were compared with test results obtained earlier for two similar panels with soft skins, i.e., panel skins with a low axial stiffness. The latter panels were shown to be more damage tolerant, which is accredited to the much smaller number of 90° plies present in the soft skins. The failure mode was found to be a three stage phenomenon: a load eccentricity is present from the start causing local bending near the damage area, impact delaminated sublaminates then buckle out of plane and eventually propagate leading to global bending and to overall instability and collapse. Delamination growth occurred mainly in the lateral direction along 90° ply interfaces, but remained within the C-scan damage area until the final unstable propagation. The stability of the damage configuration, and in particular of the sublaminates formed by the impact and the subsequent compression loading, seems to be the key with respect to the damage tolerance of heavily loaded, stiffened panels.

Impact damage in composite aircraft structures-experimental testing and numerical simulation

This paper describes a strategy for predicting internal damage in a laminated composite structure, when subjected to low-velocity impact. The aim was to obtain a better understanding of and cure for the notorious reduction in strength of aircraft compression panels when they suffered barely visible impact damage (BVID). A finite element model is presented which incorporates the non-linear behaviour due to gross deformation, interlaminar delamination and in-plane fibre and matrix failure. The strategy is validated by impact tests for a wide range of carbon/epoxy composite structures ranging from small stiff plates to realistic aircraft compression panels. It is demonstrated that the finite element model is capable of predicting impact damage in laminated composite structures and thus could be used as a design tool.

Development of lagrangian hydrocode modelling for debris impact damage prediction

Work on improving the Lawrence Livermore DYNA3D code to allow it to accurately model hypervelocity impact is presented. The unmodified version of DYNA3D was tested, results showed that improvements were required in three main areas: material modelling, the element erosion criterion, the ability to model debris cloud formed by a thin plate impact. The SESAME Equation of State has been implemented to improve the material modelling. To improve the element erosion criterion two different criterion have been implemented and tested. The first is based on total element deformation and shows improved results for semi-infinite and thin plate targets. The second is intended to delete an element when it becomes numerically inaccurate. Initial results show the limitation of the Lagrangian finite element approach and that further improvement is required.

Impact damage prediction in carbon composite structures

This paper describes a strategy for predicting the extent of internal damage in a brittle carbon fibre laminated composite stucture, when subjected to low velocity impact by a single mass. The success of the predictions, which avoid expensive three-dimensional analysis, is validated by test for a wide range of structures from small stiff plates through to large flexible stiffened compression panels whose residual strength is affected much more by internal delamination than tension structures. It is shown that a numerical model needs to incorporate nonlinear behaviour due to both gross deformations and to in-plane material degradation.

Prediction of hypervelocity orbital debris impact damage to the space station by neural networks

Prediction of damage to orbiting space craft due to collisions with hypervelocity space debris is an important issue in the design of Space Station Freedom. Space station wall structures are designed to absorb impact energy during a collision. A proposed wall structure consists of a multilayer insulation (MLI) directly covering the pressure wall, and a bumper layer placed 100mm from the pressure wall. In experiments at The Marshall Space Flight Center, 2.5–12.7 mm projectiles have been fired at this wall structure at speeds of 2–8 km/s. In this paper, three-layer backpropagation networks are trained with two sets of impact damage data. The input parameters for training are pressure wall thickness, bumper plate thickness, projectile diameter, impact angle, and the projectile velocity. Output from the network consists of hole dimensions for the bumper and the pressure wall in the minor and major axis directions, and damage to the MLI. To evaluate network generalization, networks are tested with experimental data points that are not used for training. Network performance is compared with that of other damage prediction methods. Network determination of qualitative damage estimation is suggested as a new direction for research. Preliminary testing of qualitative prediction of pressure wall damage is presented. The results are promising, and suggest several areas for further study.