The primary objective of this work is to experimentally examine the effect of various geometric parameters on the impact damage and damage tolerance of thin carbon/epoxy plate and panel structures. Due to the number of parameters involved in a low velocity impact event and the complexity of the damage created, determining what effect individual parameters have is extremely demanding, especially when some of the parameters may even be coupled. However, by experimentally simulating in a controlled manner, either the impact event or the damage created, the effect of individual geometric parameters can be isolated and determined. A quasi-static indentation test has been used to simulate an impact event. The parameters of indenter size, nose shape, plate size and boundary condition, were examined. Four different plate failure modes were identified. Indenter nose shape was found to be the dominant geometric parameter, as a change in nose shape resulted in a change in failure mode and hence maximum load. From this work, a set of geometric parameters was selected for impact testing. Impact testing at various Incident Kinetic Energies (IKE) was performed on an instrumented drop weight impact rig. From examination of internal and external damage, the development of damage to increasing IKE was determined and shown to have four distinctive phases. Coupled with strike and rebound velocity measurementsa, non-linear relationship between IKE-damage area was established and a delamination threshold energy level of 1.1 J was calculated. Damaget olerance assessmenot f impacted panels was then performed in a Compression-After- Impact (CAI) rig. Strain gauge responses allowed global and local behaviour to be compared to intact specimens. It was found that once a critical damage size was surpassed, a gradual nonlinear degradation in compressive strength was observed until a point was reached where no further degradation in performance was attained. Furthermore, propagation of internal damage in a stable and unstable manner was directly linked to the nature of sublaminate buckling behaviour. Damaget olerance assessmenot f artificially delaminatedp anels loaded in compressionw as then performed. A single artificial delamination of various size, shape and orientation, embedded at the centre of a panel was examined. Delamination width was found to be the dominant geometric parameter. Hence, when comparing a circular delamination to an elliptical one of the same area, the effect of orientation and shape is aspect ratio dependent. Finally, a comparison of impacted and artificially delaminated panels was made.

Since the horrific attacks on September 11th 2001, the United States government and research community have been focused on how to better protect US assets across the Globe. This push for safety led the research community to develop “F2656-07 Standard Test Method for Vehicle Crash Testing of Perimeter Barriers” in 2007 which standardized the method of validating a perimeter security barrier’s ability to withstand an impact from an attacking vehicle. Many of these security barriers rely on weak cohesionless soils to stop attacking vehicles. Designers currently rely heavily on hand calculations and engineering judgment when sizing these installations. This simplified analysis is generally used because of the complex nature of these soils under impact. These soils could be simulated in advanced finite element simulations; however, traditional modeling techniques will not allow for the simulation of these complex behaviors. Due to the complex nature of these simulations, new modeling techniques need to be evaluated and their use needed to be perfected. From this, a new method for creating a predictive simulation of a low speed impactor into a weak cohesionless soil was generated. This paper presents the development of a method by which a predictive simulation was created using only standard soil tests parameters. This paper also presents measured data from physical impact tests utilized to validate the method by which the simulation was generated. Next, the paper gives a detailed comparison of the results of the physical testing and the simulated impacts. The paper finally gives a summary of where the method is successful and where it needs improvement. The resulting methodology developed in this paper defines a reasonable process for creating a predictive simulation of a rigid impactor penetrating weak cohesionless sands. This finding is validated by a reasonable correlation between the measured and simulated impact penetrations. This paper also highlights the high variability of measured penetrations when testing with these soil materials.

No description available.

The <1,130 year old Whitecourt Meteorite Impact Crater, located several kilometres south of Whitecourt, Alberta (Canada), is a well-preserved bowl-shaped structure having a depth and diameter of ~6 m and 36 m. There are less than a dozen known terrestrial sites of similar size and age. Unlike most of these sites, the Whitecourt Crater contains nearly all the features associated with small impact craters including meteorites, an ejecta blanket, an observable transient crater boundary, a raised rim, and a number of associated shock indicators. The results of this study indicate that the crater formed from the impact of a type IIIAB iron meteorite travelling east-northeast at <10 km/s, striking the surface at an angle between 40 and 55 to horizontal. At present, it appears that the main mass survived atmospheric transit relatively intact to fragment and partially melt during impact, ejecting meteoritic shrapnel, most of which landed downrange.

Research Doctorate - Doctor of Philosophy (PhD) / The impact of a small particle with a wear surface can lead to very high strain-rates in the material being encountered. Often predictive erosion models are based on material property parameters taken from quasistatic test conditions. However, the material properties of the impacted wear surface can change dramatically with strain and strain-rate, leaving some doubt as to the validity of an erosion model based on quasistatic parameter values. In this study, a new stress-wave monitoring process is developed for the study of material characteristics and erosion phenomena, at strain-rates approaching 10e6s-1. For this study a newly designed piezo-electric transducer was used to monitor the stress-waves produced by small erosive particle impact events. A computational study was also conducted to aid in the transducer design and location distance from the impact source by considering the effects caused by spatial averaging. Spatial averaging affects the recorded stress-wave signal and is caused by the curvature of the stress-wave as the wave passes through the flat piezo-electric sensing element. This study was conducted using a computational and experimental approach. The joint study allowed significant knowledge to be gained for the study of elasto-plastic impact and stress-wave motion. Finite element analysis (FEA) was used to model the experimental system in detail. The stress-waves produced by the experimental process were directly compared to the FEA model. Once the FEA model was validated, detailed information from the impact event at the surface could be obtained from the model, which would otherwise be difficult if not impossible to obtain experimentally. The issues of wave dispersion have been an underlying problem in the correct interpretation of stress-wave phenomena for many years. The impact of the wear surface causes stress-waves with many frequency components, each component propagating through the wear material at distinct wave velocities. Wave dispersion causes the initial stress-wave pulse to be dispersed into many waveforms. In this study the longitudinal stress-wave was the main waveform studied. FEA simulations were conducted for a purely elastic impact and an impact causing significant plastic deformation of the surface. A comparison between these waveforms showed that in the case of impacts causing plastic deformation, the initial part of the stress-wave, measured from the time of arrival to the first peak, corresponded to the elastic stress component of the impact event at the surface. The characterisation of the waveform in regards to elastic and plastic stress components at the surface was significant for validating model parameters of the Johnson-Cook material model. The stress-wave monitoring process was applied in the first instance to erosive particle impacts to AISI 1020 steel at impact velocities up to 104m/s. A specially designed erosion apparatus, fitted with a modified double disc system was used to impact the 10mm thick steel plate. The piezo-electric transducer was firmly clamped to the rear surface, directly behind the point of impact to obtain the stress-wave signals produced by impacts of 0.4mm zirconia spheres. The study showed that the contact interface of the wear material and the piezo-electric transducer could cause a phase change and amplitude reduction of the stress-wave transmitted to the transducer at wave frequencies above 0.9MHz. The results showed that the most likely cause for the phase shift to occur was the restriction of tensile stresses across the contact interface. For wave frequencies below 0.9MHz, no phase shift or amplitude reduction was apparent in the experimental stress-wave recordings. The combined experimental / FEA study was shown to be able to validate the strain-rate parameter of the Johnson-Cook model. The parameters, which could not be validated by the stress-wave monitoring process, were the parameters relating to plastic deformation of the surface, which were the strain-hardening terms of the Johnson-Cook model. These terms were later validated by studying the extent of plastic deformation at the surface, which occurred in the form of impact craters. By comparing the predicted impact crater depths from the FEA model with the experimental results, the strain-hardening parameters of the Johnson-Cook model could be validated. The robustness of the stress-wave monitoring process was proven for the impact study of ultra high molecular weight polyethylene (UHMWPE) and vinyl ester resin (VER). Unlike AISI 1020 steel, little is know about the high strain-rate response of these polymers. Initial estimates of material property parameters were made by applying computational curve fitting techniques to the stress-strain curves of similar polymers, which were from published results obtained from split Hopkinson’s pressure bar method. The impact and stress-wave study showed UHMWPE and VER to be highly sensitive to strain-rate effects. The main effect was a substantial increase in hardness with increasing strain-rate and it was considered that the hydrostatic stress component contributed to the strain hardening of the polymers. The stress-wave monitoring and FEA computational techniques developed in this study were implemented in the development of an improved erosion model. The model form is similar to that of the well-known Ratner-Lancaster model. The Ratner-Lancaster model assumes wear rate to be proportional to the inverse of deformation energy, where deformation energy is approximated as the product of the ultimate stress and ultimate strain. The improved Ratner-Lancaster model uses the Johnson-Cook model to obtain the von-Mises stress as a function of strain. The area integral of the stress-strain curve is used to derive the deformation energy capacity of the material in the deformed zone close to the surface. The model accounts for strain, strain-rate and thermal effects and is therefore more soundly based on material deformation characteristics valid for erosion events than the Ratner-Lancaster model assumptions. The model developed in this work was applied to the erosion study of 1020 steel, UHMWPE and VER, with good correlation being obtained between experimental erosion rates and model predictions.

Thesis (S.J.D)--University of Toronto, 2005. / Source: Dissertation Abstracts International, Volume: 67-07, Section: A, page: 2729. Includes bibliographical references.

Lic.-avh. Uppsala Sveriges lantbruksuniversitet. / Härtill 2 uppsatser.

Thesis (M.Com.(Taxation))--University of Pretoria, 2009. / Abstract in English and Afrikaans. Includes bibliographical references.

Thesis (M.S.)--Ohio University, November, 1993. / Title from PDF t.p.

Thesis (Ph.D.)--University of Toledo, 2004. / Typescript. "A dissertation [submitted] as partial fulfillment of the requirements of the Doctor of Philosophy degree in Exercise Science." Bibliography: leaves 119-125.