| As a major cause of death and disability, traffic accidents have become the world’s largest public nuisance. Currently, there are about 1,300,000 people died and about 2,000,000 ~ 5,000,000 people injured in traffic accidents worldwide each year. The economic cost to developing countries is at least $100 billion a year. The United Nations General Assembly in 2010 has proclaimed the period 2011-2020 as the Decade of Action for Road Safety. The collision speed as a very important indicator for traffic accidents directly affects the severity of traffic casualties and economic loss, because the impact energy is proportional to the square of velocity. Therefore, it plays a very important role in the mechanism of traffic injuries, the road traffic laws and regulations and the responsibility in accidents. The speed identification techniques have always been hot and difficult.The traditional methods for traffic accident speed analysis are by the brake marks of tyres, the deformation of vehicles, the fallouts from the vehicles, the scratches on the vehicle body or tyres, to calculate the braking speeds and the collision speeds. With the gradual popularization of ABS and the asphalt surface, and with more and more uncertainties, fewer and fewer brake traces have been found on the road, that the traditional speed identification methods can not meet the new difficult situations. It needs to improve techniques for collision speed determination.The topic in this thesis is from the scene observation by the team of the mentor. Blocked needles have been found in a sudden that experts have imagined there might be needle impressions like fingerprints left on the gauge plates. If the decelerations were high enough to make the needle cantilever impact with the gauge plate and leave marks on it, experts could take use of them to determine the collision speed quickly. Based on this assumption, it established an experimental platform of deceleration impact to verify the assumption and to discuss its inner mechanism. Since the needle marks are usually so weak for detection by naked eyes that it takes the multiple spectrum techniques and special visualization enhancement processings to improve the detection ratio. Finally, real cases were randomly gathered to do data analysis and typical morphological maps were illustrated to do further study for their applications.This thesis is divided into three parts.Part I - Experimental study on needle marks hypotheses and mechanical model analysisIn order to verify the initial trace hypothesis, based on the physical principles in mechanical shock and vibration, the structure of cantilever with perpendicular and torsional vibration of a common mechanical speedometer has been chosen as a theoretical subject, and the mechanics between the needle and the gauge plate as well as the instant contact structures have been chosen as the research objects.The deceleration waveforms have shown that it influences the contact between the needle and the gauge plate. The needle moves as a cantilever beam during the collision. The direction perpendicular to the bottom of the cantilever vibration amplitude is significantly greater than the horizontal direction to reverse range. In the moment of impact, the gauge plate uplifts, similar to the drum membrane vibration.The contact is observed as the tip location. As long as the shaft height does not exceed the amplitude stack of the gauge plate and the needle, the needle should be in contact with the gauge plate, and left traces of collision. According to this, it brings forward Hypothesis II (the existence of middle marks independent of the tip marks).The formation of needle marks is from the amplitude of the superposition effects, which leads to the process of "contact - collision - squeeze - prints - separation" between them. This role can also be extended to the whole formation mechanism process in the field of indentation marks.It is generally considered that the farther the distal cantilever (i.e. the needle tip), the more the vibration energy is, therefore, it is more prone to contact. However, by observation in experiments, the needle cantilever beam is reciprocating complexly with gauge plate including such low-level vibrations and high vibrations with various amplitudes and frequencies which may cause the middle position (i.e. the needle bar) to leave marks on the gauge plate, for the reason that it should be more likely to leave middle marks on gauge plates than single tip marks. It eliminates the previous incompletely misconceptions about this issue, and a new hypothesis is generated which will be verified by real marks analysis in Part III.Part II - Special techniques on visualization of needle marks and image processingFor effective analysis on real sample data, critical techniques on visualization and extraction about needle marks must be developed.Firstly, it has developed multi-band waves and special image processings to do multi-spectral analysis on the suspected locations. Depth discussions are taken especially for UV fluorescence traces, and alternatives have been established for multi-spectral laser with other light sources (such as multi-wavelength LED light source) which have solved issues such as size and power consumption to meet the project needs of image acquisition and processing. This technology is essential for Group 1 and 3 (in Part III) on the sample data collection.Secondly, vapour-coating techniques have been developed to get latent needle marks which are difficult detected by the multiple spectrum technique. Vapour-coating techniques are also applicable for latent tyre marks on road surfaces. They are assistants for Group 1 and 2 in Part III.Thirdly, it has developed a quick and high accurate method for 3D measurements from 2D images. In macro, on reconstruction of the scene by teleprocessing to replace the traditional manual operations based on tape measure (for Group 2 in Part III), three types of feature marks in the matrix array have been projected. The calibrations of the camera with fixed focal length have been calculated and compared before and after revision. The cross-shaped feature is the most accurate mark. And the cone barrel with sharp apex is also more accurate than the traditional round dot. The real case practices have been engaged in to verify the practicability and efficiency of the projects which are very accurate and highly active. And for mini size measurements, as a supplementary technique (accuracy less than 0.01 mm) in measurement of needle marks identification, it is more accurate and convenient than common rulers (accuracy in 0.1 mm).These three techniques are of their independent values in applications. They are suitable not only for needle marks but also for other engineering practices.Part III - Real samples analysis and morphological maps on needle marks First, validity studies on 59 random samples collected from real cases have been down and 10 positive results have been obtained. Based on the experimental techniques developed in Part II, there are three individual groups which are Group 1 (to visualize the needle marks by optical techniques), Group 2 (to calculate the speed by traditional methods and 2D-3D measurements) and Group 3 (to do statistics and morphological categories by image processings). Different speed results are obtained isolated from Group 1 and 2, and results under same labels are then submitted to Group 3 to do morphological analysis is carried out on the final positive data, such as the typical forms of classification, the identification and the authenticity discrimination. Results have shown that, frontal collision results are significantly more accurate and reliable than traditional algorithms that they can be identified as the real speed values. There are cross sections between side impact results and traditional results, therefore, it needs to determine the speed value in combination with other information. No needle marks have been found in rear collision or other situations, so it can not draw valid conclusions. In real positive results, the lowest speed is 42 km/h, which can extend the application range from high-speed impact to general traffic areas.Second, on the basis of the case sample validity, the morphological classifications have been down on positive results under various criteria, and the left issue about the new hypothesis (in Part I) has also been effectively solved. Needle marks include tip and middle marks, single and multiple marks, scratches and impressions and visible and fluorescent marks. Each of them has independent morphological properties that experts can detect them effectively.Last but not the least, as an integral part of physical evidence researches, it must make identifications and discriminations on the authenticity of needle marks gathered from real cases. Not all needle marks can be identified, but for some clear middle marks, it can take identification between the needle bar and the impressions through mini size measurements and traces comparisons. Real tip marks are irregular short curves, which are significantly different from the forgeries. Middle marks can not be forged unless the speedometers are disassembled. It is difficult to discriminate tip scratch marks from forgeries. For multiple marks from consecutive impacts, the time order can be determined by the definition of impressions based on the energy theorem. For the needle shaft heights, gauge plate materials and collision types would influence the formation of needle marks, so it requires determining the authenticity of needle marks by combining other information in practice.In summary, by the experimental study and real case analysis of needle marks, first, it has established a reliable and practical new method for identification of vehicle collision speed. Second, it has corrected the previous misunderstanding about the relationship between impression positions and mechanism. It has provided an association with vibration mode and traces patterns, which enriches the theory of mechanical vibration and traces morphology. Third, it is the first time to draw detailed morphological maps and to do authenticity discriminations on needle marks. What is more, critical technologies, such as the multi-spectrum technology, the vapour-coating technology and the three-dimensional measurement technology, have greatly improved the detection rate of needle marks and accuracy for identifications.Although there are such innovative aspects, it is still of some deficiencies. Since similar literatures are less and real car crashes are difficult to operate for verification, for some difficult problems found during the research process, such as the quantity-effects relationship between blocked needles and collision speeds, the reflection relation between gauge plate materials and specific spectra and the association between impact velocities and traces morphological patterns, need to be in-depth studied. The method established in this study is only suitable for the determination of the medium- or high-speed frontal collision speeds, but temporarily not for the side, the rear or the low-speed frontal collision speeds. |
PDF Full Text Request