energies
Article Striated Tire Yaw Marks—Modeling and Validation
Wojciech Wach * and Jakub Z˛ebala
Institute of Forensic Research in Kraków, 31-033 Kraków, Poland; [email protected] * Correspondence: [email protected]; Tel.: +48-12-61-85-763
Abstract: Tire yaw marks deposited on the road surface carry a lot of information of paramount importance for the analysis of vehicle accidents. They can be used: (a) in a macro-scale for establishing the vehicle’s positions and orientation as well as an estimation of the vehicle’s speed at the start of yawing; (b) in a micro-scale for inferring among others things the braking or acceleration status of the wheels from the topology of the striations forming the mark. A mathematical model of how the striations will appear has been developed. The model is universal, i.e., it applies to a tire moving along any trajectory with variable curvature, and it takes into account the forces and torques which are calculated by solving a system of non-linear equations of vehicle dynamics. It was validated in the program developed by the author, in which the vehicle is represented by a 36 degree of freedom multi-body system with the TMeasy tire model. The mark-creating model shows good compliance with experimental data. It gives a deep view of the nature of striated yaw marks’ formation and can be applied in any program for the simulation of vehicle dynamics with any level of simplification.
Keywords: yaw marks striations; tire model; multibody dynamics; vehicle accident simulation
1. Introduction Citation: Wach, W.; Z˛ebala,J. The rectified projection of tire yaw marks deposited on the road surface (often either Striated Tire Yaw Marks—Modeling from an orthophotomap, a point cloud or a total station survey) can be used in a macro-scale and Validation. Energies 2021, 14, for: 4309. https://doi.org/10.3390/ • determination of subsequent vehicle positions and orientation during critical move- en14144309 ment by matching the position of individual wheels to the corresponding marks; • estimation of the vehicle’s speed at the start of yawing. Academic Editor: Aldo Sorniotti For the latter—assuming the vehicle was moving on a horizontal and homogeneous Received: 16 June 2021 surface along a curve of radius r—the critical speed formula (CSF) is most commonly used: Accepted: 15 July 2021 √ Published: 17 July 2021 v = µ·g·r, (1)
r g 2 Publisher’s Note: MDPI stays neutral where: µ—tire-to-roadway coefficient of friction, —radius of the mark, = 9.8 m/s — with regard to jurisdictional claims in gravitational acceleration. published maps and institutional affil- Although this formula may seem simplistic, it has been shown repeatedly over the iations. years that, under certain conditions, it can be considered as a quasi-empirical critical speed method (CSM). A broad overview of such conditions has been presented among others by Brach and Brach [1]. Sledge and Marshek [2] examined some refined forms of the CSF which account for the effects of, among others, vehicle weight distribution, slip angles, cornering stiffnesses and ABS. Cannon [3] has demonstrated that effective Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. braking causes the CSF to overestimate the speed at the start of the yaw mark and that This article is an open access article a 50 ft. chord appears to give acceptably low effective braking-related errors (<7%) for distributed under the terms and speeds of approximately 72 km/h (45 mph) and for speeds of approximately 97 km/h conditions of the Creative Commons (60 mph) with light to moderate braking. Cliff et al. [4] have concluded that when using the Attribution (CC BY) license (https:// peak coefficient of friction, both the CSF and simulation over-estimated the actual speed, creativecommons.org/licenses/by/ whereas slide coefficient of friction under-estimated them. Braking tended to increase the 4.0/). results. Amirault and MacInnis [5] carried out a total of 29 tests at speeds of 80 to 95 km/h.
Energies 2021, 14, 4309. https://doi.org/10.3390/en14144309 https://www.mdpi.com/journal/energies Energies 2021, 14, 4309 2 of 21
Bearing in mind non-braking and ABS braking tests, using 20 m chord measurements for the radius and the average braking coefficient of friction overestimated the measured speed by 4.1% ± 6.3% (±1σ), while using a center of gravity trajectory for the radius and the average braking coefficient of friction underestimated the measured speed by 2.0% ± 5.2% (±1σ). Lambourn [6] conducted tests in which passenger cars were freely coasting, braking or under power when travelling in a curve at speed of 55 to 100 km/h, and proposed a procedure which makes it possible to limit the uncertainty of speed calculated from the CSF to ±10%. In [7] and [8] he concluded that his previously described CSM gives satisfactory results also in the event of light braking, heavy braking with ABS, acceleration and the operation of ESP. There was no sign of the cycling of the ABS. The yaw marks had the typical appearance, practically the same as in the case of low braking without ABS. Significantly less yaw or off-tracking were observed when compared with marks deposited with little or no braking. If the brakes were applied aggressively during the yaw, the amount of yaw would decrease. This feature—the reverse of usual yawing with the heavy non-ABS braking—is probably the result of the “select low” algorithm. While most authors, notably Lambourn [6–8] and Amirault and MacInnis [5], limit their analysis to yawing with relatively low yaw rate, Cash and Crouch [9] derived a formula which accounts for a higher degree of vehicle yaw and any brake force (not only from driver input), resulting in a narrower error band than conventional CSMs. If the exact path and orientation of the collision vehicle are not readily apparent, their method allows the flexibility of considering ranges for the required values. What distinguishes simulation methods is that they provide a deep view into the time histories of curvilinear movement parameters, including the critical speed, as well as identifying a set of data (e.g., steering angle, braking/accelerating level of particular wheels, yaw moment of inertia etc.) which enables a virtual vehicle to move along the actual tire marks. The point of this article is the appearance of yaw marks in the micro-scale, that is from the perspective of the topology of striations forming the mark, which make it possible to infer the braking or acceleration status of the wheels (and sometimes even the steering angle of the front wheels). The yaw mark is essentially left by the entire tire footprint remaining in contact with the roadway (contact patch), but its blackness and distinctness depend on the local slip of the tread blocks relative to the road, and stress. The rule “the greater the stress, the more distinct the mark” applies both in the macro (when observing the entire yaw marks, the most pronounced are the marks of the external, loaded wheels) and in the micro scale (the most visible is the outer edge of a single yaw mark). Yamazaki and Akasaka in their classic article [10] argue that deposition of striations is independent of the tread pattern and is caused by an in-plane bending moment that is transmitted from the roadway to the body of the tire via the tread contact patch during sharp cornering. They refer to this phenomenon as the bending buckling behavior of a steel-belted radial tire. Buckling occurs immediately in the contact patch in the presence of a large lateral reaction from the road and is specific to radial—not bias—tires. Yamazaki in [11] shows that sharp cornering turns on steel-belted radial tires often cause wavy wear along the periphery of the shoulder. Beauchamp et al. in [12] summarize the literature concerning the yaw mark striations issue, analyze the differences in the mechanism in which striations are deposited, and discuss the relationship between tire mark striations and tire forces. They conclude that in the case of tires with pronounced shoulder blocks the striations are typically produced by these blocks whereas tires with very low pressure or without a tread pattern are more likely to deposit striations by buckling. In the absence of braking and acceleration the striation marks are parallel to the wheel rotation axis. When the brakes are applied aggressively, the striations will change to a direction more in line with the wheel trajectory but ABS prevents the tires from locking. Beauchamp et al. in [13] show examples where the striations reflect point loading of the tread shoulder blocks. In Figure1 of their article they show a mark on Energies 2021, 14, x FOR PEER REVIEW 3 of 21
Energies 2021, 14, 4309 3 of 21 striations reflect point loading of the tread shoulder blocks. In Fig. 1 of their article they show a mark on which two stripes can be distinguished: lighter striations from the inside, being deposited by the tread, and darker striations from the outside, being deposited by thewhich shoulder two stripes blocks. can A bescheme distinguished: of formation lighter of such striations a mark from they the demonstrate inside, being in deposited Fig. 3 of [13].by the tread, and darker striations from the outside, being deposited by the shoulder blocks. A scheme of formation of such a mark they demonstrate in Figure 3 of [13]. TheThe authors authors of of this this work, work, in in their their research research practice, practice, have have encountered encountered all allthe the types types of yawof yaw marks marks mentioned mentioned before—two before—two examples examples are are shown shown in in Figure Figure 1.1 .In In both both cases the vehiclevehicle was was yawing, yawing, but but the the tire tire mark mark (a) (a) was was deposited deposited by by a a buckled, buckled, zero-pressure zero-pressure tire tire duringduring a a clockwise clockwise yaw, yaw, while while the the tire tire mark mark (b) (b) was was left left by by the the leading leading shoulder shoulder blocks blocks of of thethe normal-pressure normal-pressure tire tire duri duringng a a counter-clockwise counter-clockwise yaw. yaw.
(a) (b)
FigureFigure 1. 1. YawYaw marks depositeddeposited duringduring a a full full scale scal vehiclee vehicle yaw yaw testing testing performed performed by Z˛ebalaetby Zębala al. et [ 14al.]: [14]:(a) resulting (a) resulting from from in-plane in-plane buckling buckling of a tire of a with tire zerowith pressure;zero pressure; (b) left (b by) left the by tread the shouldertread shoulder blocks blocks of a tire with normal pressure. of a tire with normal pressure.
TheThe article article by by Beauchamp Beauchamp et et al. al. [13] [13] does does an an excellent excellent job job of of analyzing analyzing yaw yaw mark mark striationsstriations from from the the viewpoint viewpoint of of its its geometry geometry and and deriving deriving equations equations for for the the calculation calculation of of longitudinallongitudinal slip slip s x usingusing the the striation striation marks marks angle angle θ andand the the slip slip angle angle α (seesee analogous analogous formulaeformulae (9) (9) and and (11) (11) derived derived in in this this article). article). It It was was shown shown that that the the model model offers offers insight insight intointo the the braking braking actions actions of of a a driver driver at at the the ti timeme the the tire marks were being deposited. The The usefulnessusefulness of of such such marks marks for for accident accident analys analysisis depends depends obviously obviously on on their their quality quality and and clarity,clarity, which which affect affect the the uncertainty uncertainty in in th thee measurement measurement of of the the geometric geometric parameters. parameters. BeauchampBeauchamp et et al. al. in in [15] [15] explore explore the the sensitivity sensitivity and and uncertainty uncertainty of of the s x equation. They They proveprove that that at at α == 5°, 5◦ ,the the striations striations will will change change over over 70 70 degrees degrees between between no no braking braking and and maximummaximum braking, whilewhile atatα = =85 85°,◦, less less than than 2 degrees2 degrees separate separate no no braking braking and and maximum maxi- mumbraking. braking. In the In first the case first braking case braking will likely will belikely easy be to easy distinguish; to distinguish; in the second, in the changessecond, changesin striation in striation angle from angle braking from braking are unlikely are unlikely to be detected. to be detected. Undoubtedly,Undoubtedly, all all researchers researchers who focus focus on on point point loading loading of of the the tread tread shoulder shoulder blocks blocks asas well well as as in-plane in-plane buckling buckling are are right right in in their their specific specific areas, areas, as as in in general, general, the the appearance appearance ofof a a striated striated mark mark left left during during curvilinear curvilinear mo motiontion depends depends on on many many factors, factors, the the main main ones ones being:being: • Camber angle of the wheel (which in turn depends on the suspension kinematics); • Structure to the tire;
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• Cornering, longitudinal and vertical stiffnesses of the tire (which depend among others things on tire pressure); • Tire aspect ratio (sidewall height divided by tire width); • Tire tread depth; • Dynamic tire offset (pneumatic trail); • Composition of rubber compound; • Road surface properties; and • Temperature in the contact patch. However, regardless of whether the striations occur from buckling or tread blocks, their direction always follows the direction of the resultant tire velocity vector in the contact patch (called the wheel slip velocity and hereinafter referred to as vIO). The only difference lies in the pitch of the striations, which in the case of striations created by the tread shoulder blocks gives the opportunity to estimate the longitudinal slip sx from the topology of the striations (according to the formula of Beauchamp et al. [13], see also Equations (9) to (12) in this article), while in the case of buckling does not give the same possibility because of lack of a buckling wave pitch (a momentary and unique period of the buckling wave). An in-depth look at the mechanics of the yaw mark creation is very interesting not only as a mathematical problem, but first of all crucial from the angle of the uncertainty of vehicle accident analysis (see e.g., [16]).
2. Assumptions to the Model For the development of a model of creating a striated tire yaw mark the following assumptions have been made: 1. To describe the tired wheel–road interaction, a semi-physical, non-linear tire model TMeasy was used [17,18]. All its features, such as longitudinal and lateral forces, aligning moment, other moments resulting from the wheel kinematics, first-order dynamics for longitudinal, lateral and torsional strain, and dynamic tire offset are taken into account. 2. The yaw mark creation model is universal, i.e., it applies to any curvilinear motion of a tire in lateral drift, when the wheel moves along any trajectory with variable curvature, and the wheel is subject to an unsteady force and moment as to the value and direction, calculated by solving the system of non-linear differential equations of vehicle dynamics. 3. As this area is in fact the dominant one, the yaw mark will be created by the tread elements of the tire shoulder forming the outer border (during curvilinear movement of the vehicle) of the patch in contact with the road. For the yaw mark curved to the left these will be the right patch border, and for the mark curved to the right the left patch border. As the striations being deposited by the internal tread elements of the patch are usually not very clear, they have been omitted; however, if necessary, it will be easy to extend the algorithm by following the model described. 4. It is possible to define any, including non-uniform, pitch of the tread shoulder blocks of the tire. 5. Semi-physical tire models of class TMeasy, Magic Formula [19], HSRI [20] etc. do not describe the tire in-plane buckling, therefore this phenomenon can instead be analyzed in two ways: (a) partially, i.e., as to the tire mark course and the striations direction only; it is then sufficient to enter any pitch of the tread shoulder blocks; (b) fully, i.e., as to the tire mark course, and striations direction and pitch, if the buckling pitch in the patch is known in some other way, which can be manually entered into the program.
3. Basic Terms Concerning Movement of a Wheel in a Bend A concise, computer-friendly vector-matrix notation has been used. The italic small letters (e.g., v) mean scalars, bold small letters (e.g., v)—vectors, and bold capital letters Energies 2021, 14, x FOR PEER REVIEW 5 of 21
3. Basic Terms Concerning Movement of a Wheel in a Bend Energies 2021, 14, 4309 5 of 21 A concise, computer-friendly vector-matrix notation has been used. The italic small letters (e.g., ) mean scalars, bold small letters (e.g., )—vectors, and bold capital letters (e.g., )—matrices. In the vector-matrix equations the Rill’s subscript notation [18] has been(e.g., used:A)—matrices. In the vector-matrix equations the Rill’s subscript notation [18] has been used: {} the symbol of a reference frame, e.g., the term {I} should be read “in the reference {} framethe symbol I”; of a reference frame, e.g., the term {I} should be read “in the reference frame I”; {I} the ground-fixed inertial (global) reference frame with the origin at point I; the axis {I} isthe parallel ground-fixed to the gravitational inertial (global) acceleration reference vector frame with and thepoints origin upward; at point I; the zI axis is parallel to the gravitational acceleration vector g and points upward; , vector from point I to wheel center O; the subscript after the comma denotes the ref- rIO,Ierencevector frame from in point whichI to this wheel vector center is observed—hereO; the subscript {I}; after the comma denotes the reference frame in which this vector is observed—here {I}; , vector of absolute velocity of wheel center O, with respect to {I}. vIO I vector of absolute velocity of wheel center O, with respect to {I}. ,A characteristic point of the tire-road patch Q, which is the origin of the Cartesian A characteristic point of the tire-road patch Q, which is the origin of the Cartesian coordinate system with unit vectors on its axes , , (shown in Figure 2a), is referred coordinate system with unit vectors on its axes e , e , e (shown in Figure2a), is referred to as the contact point. In the TMeasy tire model, thex systemy n of forces acting on the wheel to as the contact point. In the TMeasy tire model, the system of forces acting on the wheel is reduced to an equivalent system of forces ( , and ) and their moments ( , and is reduced to an equivalent system of forces (F , F and F ) and their moments (M , M ), whose directions of action coincide with thex directionsy z of the unit vectors. The posi-x y and M ), whose directions of action coincide with the directions of the unit vectors. The tion of thez rim center plane in relation to the road is determined by the position vector position of the rim center plane in relation to the road is determined by the position vector and the unit vector , normal to this plane and defining the wheel rotation axis. rIO and the unit vector eky, normal to this plane and defining the wheel rotation axis.
(a) (b)
FigureFigure 2. 2. VelocitiesVelocities in in the the process process of of depositing depositing striations striations by by tire tire shoulder shoulder blocks blocks during during yaw: yaw: (a ()a ) perspective;perspective; (b (b) )top top view. view.
CamberCamber γ asas well well as as cornering cornering cause cause the tire toto deflectdeflectlaterally laterally and and to to offset offset the the contact con- tactpoint pointQ against Q against the the rim rim center center plane plane by by the the distance distanceye (see (see Section Section 5.3 5.3).). The The road road surface sur- facegeometry geometry in { Iin} defines{I} defines the the function: function: