Dynamic Impact Testing

Dynamic properties, fracture toughness, fracture energy, dynamic modulus, dynamic testing, impact tests, drop tower, high strain rate. 

Chapters 6 and 7 refer to two practical case studies, in particular two fuel cell propulsion systems of different size. Here the technical characteristics of all individual components are described, and the results of an experimental characterization carried out on laboratory dynamic test benches are discussed. The findings of these two chapters evidence the limitations and potentialities of fuel cell power trains at the present state of development, in terms of performance, efficiency, environmental impact and durability. 

From the physical point of view, the Izod equipment is equivalent to that of Charpy. However, the main differences between the two are the clamping system, the notch, the hammer speed and its weight. Charpy adopted the keyhole form of notch. At such an early stage in the history of impact testing, Charpy found that correlations between static and dynamic tests were obtainable provided a notched bar was used. In 1925, the Izod and Charpy tests were extended to plastic materials and many results on plastics were pub-hshed a year later [Werting, 1926]. 

It should be noted that the composites damage and failure models discussed here are based on an assumption of rate-independent behaviour, and materials properties used for validation studies are based on quasi-static tests. This is currently standard practice in impact simulations of composite structures, which is an important assumption in the work. Reasons for this are the lack of international dynamic test standards for measuring rate-dependent composites properties, so established test procedures are missing. Dynamic failure models for composites are not well understood nor implemented in current commercial FE codes. In justification it should be pointed out that carbon fibres are highly elastic, thus fibre-dominated properties show no... 

A summary of the test conditions and results is detailed in Table 10.2, which shows total mass inclusive of drop sled, I-beam, added mass and mass of frame stmcture, the absorbed energy by the frame stmcture and the cmsh distances. The measured force—displacement curves from the quasi-static and dynamic tests are presented in Figure 10.16. The load levels plotted for each of the tests conducted are a summation of the three force transducers in the impact platform. These curves exhibit characteristics typical of those seen in Section 10.3 for progressively cmshed... 

Kalthoff J.F. (1993) On the validity of impact energies measured with polymeric specimens in instrumented impact tests. Impact Dynamic Tract Polym Compos ESIS, Vol. 19. 

The main dilferences between conventional quasi-static mechanical testing and a dynamic impact event on large samples have been well demonstrated in the open literature. Generally, the strain rate for quasi-static mechanical testing is on the order of lO -lO s while dynamic testing is in the range of 10 -10" s Therefore, the stressed volume in an impact event is much larger than that in the... 

Fig. 10.26 Hypothetical dynamic shock stress waves/energy profiles in an edge-on impact (EOI) test. Reproduced with permission from [172], Copyright 2013, Springer Science + Business Media...

Settlement-rotation plots have been widely used by researchers to explore the impact of different test parameters on the dynamic behavior of shallow fotmdations (Gajan et al. 2005 Gajan and Kutter 2008, 2009 Anastasopoulos et al. 2009 Kutter and Kunnath 2010). However, the majority of the available literature collates the data from numerical analysis, slow pseudo-dynamic testing or small-scale 1-g testing. Geo-PIV techniques allow settlement-rotation plots to be produced from true dynamic testing. 

It is necessary, therefore, to test an adhesive by many techniques to simulate the conditions that it may be subjected to in service. The three types of tests to be discussed are tensile, shear, and peel. These tests are the most common and result in information which is useful for reliable joint design. Response to dynamic testing such as fatigue, creep, and impact will also be introduced. 

Gruenbaum and Miltz [76] found that the amount of energy absorbed in low strain compression tests and impact tests is almost the same, while the force applied to the product is about 30-50% higher in the dynamic test. Therefore, there is a need for reliable data under impact conditions. 

As an application of the theory discussed earlier, the crash responses of aircraft occupant/stnicture will be presented. To improve aircraft crash safety, conditions critical to occupants survival during a crash must be known. In view of the importance of this problem, studies of post-crash dynamic behavior of victims are necessary in order to reduce severe injuries. In this study, crash dynamics program SOM-LA/TA (Seat Occupant Model - Light Aircraft / Transport Aircraft) was used (13,14]. Modifications were performed in the program for reconstruction of an occupant s head impact with the interior walls or bulkhead. A viscoelastic-type contact force model of exponential form was used to represent the compliance characteristics of the bulkhead. Correlated studies of analytical simulations with impact sled test results were accomplished. A parametric study of the coefficients in the contact force model was then performed in order to obtain the correlations between the coefficients and the Head Injury Criteria. A measure of optimal values for the bulkhead compliance and displacement requirements was thus achieved in order to keep the possibility of a head injury as little as possible. This information could in turn be usm in the selection of suitable materials for the bulkhead, instrument panel, or interior walls of an aircraft. Before introducing the contact force model representing the occupant head impacting the interior walls, descriptions of impact sled test facilities, multibody dynamics and finite element models of the occupant/seat/restraint system, duplication of experiments, and measure of head injury are provided. 

Use of impact sled tests is the most common technique for determining the postcrash dynamic behavior of an aircraft occupant. The impact sled and target tracking facilities available at National Institute for Aviation Research (NIAR) were used to conduct a study on occupant responses in a crash environment. Parallel analysis capabilities, including a multibody dynamic model of the occupant and a finite element model of seat structures, have been developed. The analysis has been used to reasonably predict the Head Injury Criteria (HIC) as compart with the experimental impact sled tests for an occupant head impacting a panel. A nonlinear viscoelastic contact force model was shown to better predict the experimental data on the contact forces than the Hertzian models. Suitable values of the coefficients in the contact force model were obtained and the correlations between the coefficients, HIC, and maximum deformation of the front panel were determined. A non-sled test method of pendulum-type has been designed to determine the head injuries as well as the performance of each particular impact absorber. 

Reactor safety modeling and testing, to better understand impact dynamics and effect on reactor design. 

Keywords instrumented impact test, Charpy test, Izod test, fracture resistance, striker, strain gages, dynamic testing... 

Clausen, A. H. et al.. Polymer plates subjected to impact Experimental tests and numerical simulations, DYMAT 2009 9th International Conference on the Mechanical and Physical Behaviour of Materials under Dynamic Loading, 2,1537-1543, 2009. 

---