The nature of the collision of cars. Transport and traceological expertise. By the initial mutual arrangement of objects

As a result of a collision of a vehicle, as well as when they hit an obstacle and run over people, various traces appear on them. Some of them appear as a result of the initial impact, others - during their subsequent movement (hitting a pole or barrier, overturning, going into a ditch). When analyzing the overall picture of the tracks, great importance is attached to the identification of traces of the initial contact, since by studying them, it is possible to establish such components of the accident mechanism as the direction of movement, the angle of collision, the relative position of the vehicle at the moment of collision, etc.

Traces of a primary impact (contact) appear immediately at the moment of impact on an obstacle, they usually take the form of extensive deformations, dents, scoring, scratches, paint peeling, etc.

Collisions can be divided into three main types:

Passing - occur when the vehicle moves in one direction:

Oncoming - when the vehicle moves in opposite directions;

Corner (transverse) - when the vehicle moves at an angle to each other.

A variety of oncoming and passing collisions is a side sliding collision, i.e. collision of the vehicle with its lateral sides (almost a sliding impact), in which the vehicles practically do not change their direction of movement (of course, if the difference in their masses is very insignificant).

A type of lateral collision is a cross collision, when vehicles collide at right angles, i.e. the longitudinal axes of the colliding vehicles are relatively perpendicular.

When inspecting vehicles, first of all, attention is paid to the places most severely affected by the impact, in which the direction of deformation is clearly visible. Depending on the type of collision, traces are located on certain parts of the vehicle. In a passing collision, traces of primary contact are located at the front of one vehicle (on the front bumper, fenders, radiator grille, hood, broken windshields, headlights and sidelights can be added to these tracks), at the other - at the rear (on the rear wall of the body, rear bumper, on towing hooks). Damage to rear lights, reflectors is also characteristic, paint and wood may peel off; in addition, the rear axle may be damaged. In an oncoming collision, impact damage is located on the front parts of both vehicles - on the front bumpers, facings, hoods, fenders, front parts of the cab. This type of collision is characterized by damage to headlights, sidelights, windshields. As a result of a significant impact and deformation, the glass of the cab doors may be damaged, the doors may jam. In a head-on collision, a heavier vehicle is capable of crushing a lighter one; in this case, traces of protruding parts of a heavy vehicle and even of its wheels may remain on the upper surface of the latter (on the front hood, roof of the body, etc.). In a corner collision, one of the vehicles causes damage to the front or rear corners. As a result of a strong impact, the front axle can be torn off the kingpin, the footboard, headlights and sidelights, the wheels are separated, the front bumper is bent or crushed, the windshield is broken. A lateral sliding collision is characterized by the breakdown of protruding parts and parts of the vehicle located in the side parts (corners of bumpers for some types of cars, steering for cyclists and motorcycles, side parts of the driver's cab, fenders, door handles, external rear-view mirror, body steps). In sliding side collisions, contact traces are dynamic. From them you can determine the direction of the impact. A cross-collision is characterized by the formation of traces in one vehicle on the front parts in the same places as in an oncoming collision, and in the other - on the side ones (on the fender, steps, side of the cab or body, on the door, wheels, muffler, gas tank of the car) ...

Traces of primary contact in a collision arise from the introduction of parts of one vehicle into another. Primary contact is characterized by many dents, displacements of the metal in a certain direction (to the sides opposite to the direction of the impact force, i.e. the movement of the vehicle).

Dynamic traces are formed at the moments of the introduction of parts of one vehicle into another and end in dents, at the bottom of which there may be displays of trace-forming parts and parts or holes. They are also located in the direction of metal deformation and are pronounced in the form of scratches, metal cuts, scuffs with breaks, as well as the imposition and peeling of paint or rubber (from the wheels).

Localization of damage depends on the type of collision. Tracks formed in a collision are much more pronounced than tracks formed during subsequent impacts or overturning of the vehicle.

Areas of primary contact are determined at the location of the greatest deformation of the metal, located in one direction.

Damage to vehicles resulting from their overturning can be easily distinguished from other types of damage. When overturning, the vehicle is subjected to loads that are different from the loads experienced by them in a collision. Some of their parts (for example, the radiator grille) are not damaged in this case, others (for example, the bumper) are less damaged than in a collision. In the process of overturning, the vehicle usually comes into contact with the road surface with the cab roof, which is crumpled in this case. Extensive damage (dents, bent struts) is formed on parts of the vehicle made of thin sheet steel, as they are easily subject to deformation. The resulting damage does not have a strictly defined direction, i.e. deformation of the metal occurs in different directions. In places where dents are formed, there are dynamic and static traces from contact with the road and various objects on it (dirt, gravel, sand, branches). These tracks also do not have a clear definite direction.

Traces of secondary contact can be either a continuation of the traces of primary contact from a collision with a vehicle, or a trace from an impact on other objects (a corner of a house, a pole, a tree). Traces of secondary contact are usually less pronounced than traces of primary contact, since part of the kinetic energy at the moment of primary contact in a collision of a vehicle is lost. The deformation of the metal in these traces is either a continuation of the deformation of the primary contact (then their direction coincides), or has a different direction.

In case of corner and cross collisions, the vehicle often "folds" and traces of secondary contact are formed on the lateral sides.

Lateral collision (sliding) is characterized by the presence of traces of primary and secondary contact of the same intensity. Traces of secondary contact (dents, scratches, burrs, paint layers) here are a continuation of traces of primary contact and are located on the side surfaces of the vehicle.

If in a side collision the driver of the car loses control, a collision with a stationary object may occur, then the deformation of the parts of the vehicle has a different direction. Vehicle deformation configuration displays the configuration of the collision object.

When performing an examination in the course of establishing traces of primary contact and the sequence of damage formation, it is necessary to take into account all damage that occurred during the accident. They can be located not only on the vehicle itself, but also on the road (rollover marks) and on objects with which a collision occurred.

Only by evaluating all the traces in aggregate and comparing them with each other, it is possible to correctly establish the place of primary contact and resolve the issue of the sequence of damage formation.

Thus, a collision of MAZ-503 and UAZ-452 vehicles occurred on the Moscow Ring Road. Both cars followed the same direction. Due to the discrepancy between the readings of the drivers of both vehicles, it was necessary to determine the place of the primary contact between the vehicles and the cause of the damage to the rear side of the UAZ-452 vehicle. During an expert examination of the vehicles, it was found that the left side of the UAZ-452 vehicle platform was destroyed. It had damage in the form of dents and scratches directed from front to back, on the rear side of the car body - numerous multidirectional scratches, and there were no impact marks. On the MAZ-503 car, the right wing was damaged, there were traces of impact (dents, holes) and traces of sliding (scratches) on it.

When comparing the damage on the UAZ-452 car body with the damage on the MAZ-503 car, it turned out that the damage on the left side of the UAZ-452 car body coincides in nature, size, distance from the road surface with the damage to the right wing of the MAZ-503 car. Analysis and comparison of the damage allowed the expert to conclude that the initial contact occurred with the left side of the UAZ-452 vehicle with the right wing of the MAZ-503 vehicle.

Analysis of the damage to the rear side of the UAZ-452 car body, taking into account the sliding marks recorded in the protocol of the inspection of the scene of the incident and the diagram to it, made it possible to establish that they were formed when the UAZ-452 car rolled over after a collision and when it slipped on the road surface.

In the event of a vehicle hitting a pedestrian, the following options are possible.

1. In case of collision with the front of the vehicle, a blow to the body is possible, in which the victim will be thrown in the direction of traffic.

In this case, the car will be damaged only from primary contact - on the front parts in the form of dents, abrasions, blood stains, layers of clothing and shoes particles.

When hitting with the front part, it is also possible to throw the victim's body onto the vehicle and move it in the direction opposite to the vehicle's movement. In this case, secondary traces remain, often dynamic, in the form of sliding traces (abrasions, scratches, layers of clothing particles, blood, brain matter) on the fender, hood, driver's cab, body of a car.

If the body of the victim is thrown in the direction of travel, the vehicle may run over him. Traces of crossing usually remain on the lower parts of the vehicle (on wheels, front and rear axles, cardan of a truck, gearbox, etc.).

2. When hitting with the rear part of the vehicle (in the case of its reversing), a blow usually occurs or the body is pressed by the car to a foreign object (against a wall of a building, a tree): there are no traces of repeated contact between the vehicle and the victim's body. The exceptions are cases when the body is sandwiched between the side surface of the vehicle and some obstacle and is dragged between them.

3. In case of a sliding impact by the side part of the vehicle, the body of the victim is thrown aside in the direction of traffic. In this case, repeated contact, as a rule, is impossible, in rare cases, the car can run over the victim's body.

To establish traces of primary contact when hitting a pedestrian, it is necessary to carefully familiarize yourself with the act of forensic medical examination of the victim, examine the damage on his clothes and shoes and compare them with the damage to the vehicle.

To understand the scale of damage to a car after an accident, one must clearly understand what happens immediately at the moment of impact with the car body, which areas are subject to deformation. And you will be unpleasantly surprised to learn that in a frontal impact, the rear part of the body is skewed.

Accordingly, after an unscrupulous body repair of the front end, even if the car was on the slipway, you will observe a sticking of the trunk lid, rubbing of the sealing gum, and much more. center.

General information

Theory collisions – this knowledge and understanding forces, emerging and acting at collision.

The body is designed to withstand shocks from normal traffic and to ensure the safety of passengers in the event of a collision. When designing the bodywork, special care is taken to ensure that it deforms and absorbs the maximum amount of energy in a serious collision, and at the same time has a minimum impact on passengers. For this purpose, the front and rear parts of the body must deform easily to a certain limit, creating a structure that absorbs the energy of an impact, and at the same time, these parts of the body must be rigid in order to maintain the compartment for passengers.

Determination of violation of the position of body structure elements:

• Knowledge of collision theory: understanding how a vehicle's structure reacts to the forces of a collision.
• Body inspection: Search for signs that indicate structural damage and its nature.
• Measurements: basic measurements used to identify violations of the position of structural elements.
• Conclusion: applying knowledge of collision theory in conjunction with the results of an external examination to assess the actual position violation of a member or structural members

Collision types

When two or more objects collide with each other, the following collisions are possible

By the initial mutual arrangement of objects

• Both objects are moving
• One is moving and the other is motionless
• Additional collisions

In the direction of impact

• Frontal collision (frontal)
• Collision from behind
• Side collision
• Rollover

Let's consider each of them

Both objects are moving:

One is moving and the other is motionless:

Additional collisions:

Frontal collision (frontal):

Rear collision:

Side collision:

Rollover:

Influence of inertial forces in a collision

Under the action of inertial forces, a moving car tends to continue moving in a forward direction and, when it hits another object or car, acts as a force.

A car that is stationary strives to remain stationary and acts as a force opposing another car that has run over it.

When colliding with another object, an "External Force" is created

As a result of inertia, "Internal forces" arise

Damage types

Impact force and surface

The damage will be different for given vehicles of the same mass and speed, depending on the collision object, such as a pillar or wall. This can be expressed by the equation
f \u003d F / A,
where f is the magnitude of the impact force per unit surface
F - strength
A - impact surface
If the impact hits a large surface, the damage will be minimal.
Conversely, the smaller the impact surface, the more severe the damage will be. In the example on the right, the bumper, hood, radiator, etc. are seriously deformed. The engine is pushed back and the consequences of the collision extend to the rear suspension.

Two types of damage

Primary damage

A collision between a vehicle and an obstacle is called a primary collision and the resulting damage is called a primary damage.
Direct damage
Damage caused by an obstacle (external force) is called direct damage.
Ripple damage
Damage caused by the transfer of impact energy is called ripple damage.
Damage caused
Damage caused to other parts experiencing tensile or pushing forces as a result of direct damage or ripple damage is called induced damage.

Secondary damage

When the car hits an obstacle, a large deceleration force is generated, which stops the car within a few tens or hundreds of milliseconds. At this point, passengers and objects inside the car will try to continue moving at the speed of the car before the collision. A collision that is caused by inertia and occurs inside the vehicle is called a secondary collision, and the resulting damage is called secondary (or inertial) damage.

Categories of violation of the position of parts of the structure

• Forward displacement
• Indirect (indirect) offset

Let's consider each of them separately

Forward displacement

Indirect (indirect) offset

Shock absorption

The car is divided into three sections: front, middle and rear. Each section, due to its design, reacts independently of the others in a collision. The car does not react to impact as one inseparable device. On each section (front, middle and rear), the effect of internal and / or external forces is manifested separately from other sections.

Places of car division into sections

Impact absorption design

The main purpose of this structure is to effectively absorb the impact energy of the entire body frame in addition to the destructible front and rear parts of the body. In the event of a collision, this design ensures a minimum level of deformation of the passenger compartment.

Front part of the body

Since the front end of the body has a relatively high collision probability, in addition to the front side members, there are upper wing apron reinforcements and upper side dash panels with stress concentration zones to absorb impact energy.

Rear part of the body

Due to the complex combination of rear side panels, rear floor box and spot welded elements, shock absorption surfaces are relatively difficult to see at the rear, although the concept of shock absorption remains the same. Depending on the location of the fuel tank, the impact absorption surface of the rear floor side members has been modified to absorb impact energy from collisions without damaging the fuel tank.

The ripple effect

Impact energy is characterized by the fact that it easily passes over the strong parts of the body and finally reaches the weaker parts, damaging them. The principle of the ripple effect is based on this.

Front part of the body

In a rear-wheel drive vehicle (FR), if an impact energy F is applied to the leading edge A of the front side member, it is absorbed by damaging zones A and B and also causes damage to zone C. The energy then passes through zone D and, after changing direction, reaches zone E. Damage, created in area D is shown by the rearward offset of the spar. The impact energy then causes ripple damage to the instrument panel and floor box before spreading over a wider area.

In a front wheel drive (FF) vehicle, the frontal impact energy will cause intense destruction of the front section (A) of the side member. The impact energy, causing the rear end B of the side member to bulge, ultimately causes ripple damage to the instrument panel (C). However, ripple effects on the rear (C), reinforcement (lower rear side member) and steering bracket (lower instrument panel) remain negligible. This is because the center of the side member will absorb most of the impact energy (B). Another characteristic of a front wheel drive (FF) vehicle is damage to the engine mounts and adjacent areas.

If the impact energy is directed towards section A of the wing apron, the weaker sections B and C along the path of the impact energy will also be damaged, allowing some of the energy to be extinguished as it propagates backward. After zone D, the wave will act on the top of the pillar and the roof sill, but the effect on the bottom of the pillar will be negligible. As a result, the A-pillar will tilt backward, with the bottom of it acting as a pivot (where it connects to the panel). The typical result of this movement is a shift in the landing zone of the door (the door becomes offset).

Rear part of the body

Impact energy on the rear sidewall panel causes damage in the contact area and then at the tailgate sidewall. Also, the rear side body panel will slide forward, eliminating any gap between the panel and the tailgate. If higher energy is applied, the tailgate can be pushed forward, deforming the B-pillar, and damage can propagate to the front door and A-pillar. Door damage will concentrate in the bent areas at the front and rear of the outer panel and in the door lock area of \u200b\u200bthe inner panel. If the pillar is damaged, a poorly closing door is a typical symptom.

Another possible direction of the ripple effect is the path from the tailgate pillar to the roof runner.

In this case, the rear of the roof rafter will push upward, creating a larger gap at the rear of the door. The joint between the roof panel and the rear side body then deforms, causing the roof panel above the B-pillar to deform.

The place of collision of the vehicle can be established according to the signs recorded in the case materials (inspection protocols, diagrams, photographs). The information content of these signs is different. Some make it possible to establish the location of the collision with sufficient accuracy, others - approximately, the third can only be an additional confirmation of the location of the collision point, determined in other ways. The conclusion about the location of the collision site should be based on a study of the totality of all such signs.

The main signs by which the place of collision of the vehicle is established can be divided into 5 groups: traces of vehicle movement; traces of the movement of discarded objects; location of objects separated from the vehicle; location of the vehicle after the accident; damage to the vehicle received in a collision.

The first group of tracks is characterized by the following features:

A sharp deviation of the wheel track from the original direction (with an eccentric impact on the vehicle or on the front wheel);

Lateral shift of an unlocked wheel or lateral shift of the track skid of the wheel (most accurately determines the position of the vehicle in a collision);

The cessation of the skid trace occurs upon impact as a result of additional load on the wheel;

Formation of a wheel slip trace when jammed by deformable parts;

Formation of a wheel trace when air comes out of a tire damaged by an impact;

Wheel tracks of both vehicles before the collision (determine the position of the vehicle at the moment of collision at the place of their intersection, taking into account the relative position during the impact);

Traces of friction of vehicle parts on the road surface during deformation of the body or destruction of the chassis at the moment of impact.

The second group of tracks is characterized by the following features:

Traces of heavy objects (parts detached from the vehicle, dropped cargo, etc.) in the form of scratches, abrasions. At the beginning of their formation, they are directed to the place of separation from the vehicle (close to the place of collision).

Determination of the collision site at the intersection of the directions of such traces is the more accurate, the more they are installed.

The third group of traces is characterized by the location of objects separated from the vehicle:

Sprinkle earth (dirt) from impact deformable and other lower surfaces of the vehicle. A scatter of the smallest particles remains almost directly at the impact site. Larger particles can move by inertia in the direction of vehicle movement. For a more accurate determination of the location of the vehicle at the moment of impact, it is necessary to know which vehicle the fallen earth belongs to;

Area of \u200b\u200bdispersion of particles of paintwork (LCP). These particles, possessing low inertia, fall in the immediate vicinity of the collision site and are partially scattered in the direction of vehicle movement after the impact. Perhaps their displacement by air flows;

Plot of broken glass. Allows you to approximately judge the location of the collision when their free fall was not impeded by surfaces from which ricocheting could occur. The location of the largest number of objects separated from the vehicle upon impact makes it possible to judge the place of the collision approximately, taking into account their possible displacement from the place of collision after the impact. The location of individual large parts, as a rule, cannot serve as a sign for establishing the place of collision.

The fourth group of tracks is the location of the vehicle after the accident:

The location of both vehicles after a longitudinal head-on collision on one side of the carriageway is a sign that the collision occurred on the same side of the carriageway;

The location of both vehicles in the immediate vicinity of the collision site when driving in the opposite direction with parallel courses before the collision makes it possible to determine the lateral displacement of the center of gravity of one of them from the place where the impact was struck.

Fifth group of footprints- damage to the vehicle received in a collision:

The location of damage to the vehicle from contact with each other makes it possible to determine their relative position at the moment of collision and to clarify the place of collision, if the location and direction of movement of one of them at the moment of collision are established;

The direction of deformations, which determines the direction of the impact, allows you to establish the possible displacement of the vehicle from the place of collision and by its location after the accident to clarify the place of collision;

Vehicle collision mechanism - this is a complex, connected by objective laws, of the circumstances that determine the process of convergence of vehicles before a collision, their interaction during the impact and the next movement to a stop. Analysis of the data on the circumstances of the incident creates an opportunity for the expert to establish the relationship between individual incidents, fill in the missing links and determine the technical cause of the incident. A formal decision by an expert of a question on the basis of separate disparate data, without a technical assessment of their mutual correspondence and the correspondence of certain objective data, without identifying and explaining the contradictions between them, may lead to incorrect conclusions.

When investigating the mechanism of an incident, signs that directly allow one to establish a particular circumstance may be absent. In many cases, the mechanism can be determined based on data about other circumstances of the incident, by conducting expert research on the basis of patterns that combine all the circumstances of the mechanism into one chain.

THREE STAGES OF THE COLLISION MECHANISM

The vehicle can be divided into three stages: the approach of the vehicle before the collision, their interaction upon impact, and throwing away (movement after the collision).

First stage - the process of approaching begins from the moment a hazard to road traffic arises, when the driver must immediately take the necessary measures to prevent an accident (or reduce the severity of the consequences), and ends at the moment of the initial contact of the vehicle. At this stage, the circumstances of the incident are most determined by the actions of its participants. In the following stages, the incident mainly unfolds under the influence of irresistible forces arising in accordance with the laws of mechanics. Therefore, in order to resolve issues related to the assessment of the actions of the participants in the accident, from the point of view of their compliance with traffic safety requirements, it is of particular importance to determine the circumstances of the accident at its first stage (the speed and direction of the vehicle before the accident, their location along the width of the carriageway).

Some circumstances at the first stage cannot be established directly on the spot or by expert interrogation of witnesses. Sometimes they are clarified by expert examination of the collision mechanism in the following stages.

Stage two - vehicle interaction - begins from the moment of their initial contact and ends at the moment when the action of one vehicle on the second one stops and they begin to move freely.

The interaction of a vehicle in a collision depends on the type of collision, it is determined by the nature of the impact, which can be blocking and sliding. With a blocking impact, the vehicles seem to be interlocked in separate sections, and there is no slippage between them. With a sliding impact, the contacting areas are displaced relative to each other.

The process of collision of a vehicle with a blocking blow can be divided into two phases.

In the first phase, deformation of the contacting parts occurs due to their mutual penetration. It ends at the moment when the relative speed of the vehicle falls to zero in the contact area and lasts for a fraction of a second. Huge impact forces, reaching tens of tons, create large decelerations or accelerations. With eccentric impacts, angular accelerations also occur. This leads to a sharp change in speed, the direction of movement of the vehicle and their turn. But since the impact time is negligible, the vehicle does not have time to significantly change its position during this phase; therefore, the general direction of deformations mostly almost coincides with the direction of the relative velocity.

In the second phase of the blocking impact, after the completion of the mutual penetration of the contacting areas, the vehicles move relative to each other under the action of the forces of elastic deformations, as well as the forces of mutual repulsion arising from an eccentric impact.

The size of the impulse of elastic deformation forces is rather small compared to the impulse of impact forces. Therefore, with a slight eccentricity of the impact and deep penetration of the contacting parts, the adhesion forces between them can prevent the vehicle from separating, and the second phase can end before their separation.

A sliding collision occurs in cases when the velocities in the contact areas do not equalize and, before the vehicle begins to separate from one another, the interaction occurs sequentially between their various parts located along the line relative to the displacement of the contacting areas. With a sliding impact, the vehicle manages to change its relative position in the collision, which somewhat changes the direction of deformations.

The second stage of the collision mechanism links the first and third stages of it, which, under certain conditions, makes it possible to determine the circumstances of the accident at the first stage, based on the results of the study of the traffic situation after the accident.

Third stage - the process of throwing away (movement after a collision) begins from the moment of termination of interaction between vehicles and the beginning of their free movement, ends at the moment of completion of movement under the influence of resistance forces.

The collision mechanism at this stage is determined by the results of the impact of the forces of impact on the vehicle - dropping the vehicle, separating and dispersing parts, debris, spraying liquid. Therefore, the most complete data required to clarify the collision mechanism can be obtained by examining and investigating the scene of the accident.

When examining the collision mechanism during the approach of the vehicle, the expert establishes either a violation of stability or loss of controllability before a collision and the reasons for such a violation, determine the speed of the vehicle before the accident and at the moment of collision, establish their location at certain times, lane, direction of movement, angle of meeting at collision.

Investigating the process of interaction between vehicles, the expert establishes their mutual position at the moment of impact, determines the direction of the impact and its impact on the studied movement.

When examining the process of dropping a vehicle after a collision, the expert establishes the place of the collision by the remaining tracks and the location of the vehicle after the accident, determines their movement speed after the impact, the direction of dropping.

The establishment of the collision mechanism by the expert and the technical assessment of the actions of the participants in the incident allow the investigating authorities and the court to decide the issue of the cause of the incident and the circumstances that contributed to its occurrence.

The method of expert research in establishing the collision mechanism depends on the type of collision. According to the main classification criteria that determine the collision mechanism, all vehicle collisions can be divided into the following groups:

In the angle between the directions of vehicle movement - longitudinal (when driving parallel or close to a parallel course) and cross collisions. Longitudinal collisions are subdivided into oncoming and passing;

By the nature of the interaction in the contact area during impact - blocking (with complete damping of the relative velocity at the moment of impact), sliding and tangential collisions.

These features characterize the collision mechanism of both vehicles. In addition, the collision of each of the two colliding vehicles can be characterized by signs inherent only to this vehicle:

By the nature of the movement immediately before the strike - a collision without a reserve, with a reserve to the right or to the left;

At the place of application of the shock impulse - the collision is lateral right - or left-sided, front, rear, angular;

In the direction of the impact impulse - the collision is central (when the direction of the impact passes through the center of mass of the vehicle), right - or left eccentric.

This collision classification system makes it easy to formalize the collision characterization.

§ 2. Mechanism of collision of vehicles

General concept of the collision mechanism

The collision mechanism of a vehicle is a complex of circumstances connected by objective regularities that determine the process of approaching vehicles before a collision, and interaction during an impact and subsequent movement to a stop, analysis of data on the circumstances of an accident allows an expert to establish the relationship between individual events, fill in the missing links and determine the technical reason incidents. A formal solution by an expert of questions on separate disparate data, without a technical assessment of their compliance with each other and established objective data, without opening and explaining the contradictions between them, can lead to incorrect conclusions.

When investigating the mechanism of an incident, signs that directly allow establishing a particular circumstance may be absent. In many cases, it can be established on the basis of data on other circumstances of the incident, by conducting an expert study on the basis of regularities linking all the circumstances of the incident mechanism into a single set.

Features of impact in a collision

The theory of impact is based on ideal conditions that greatly simplify the concept of the interaction of bodies during impact. So, it is assumed that the contact of the colliding bodies occurs at one point through which the interaction force passes, that the surfaces of the colliding bodies are absolutely smooth, there is no friction and engagement between them. Therefore, the impact force is perpendicular to the plane tangent to the surface of the colliding bodies at the point of their contact. The duration of the impact is taken to be zero, and since the impulse of force has a finite value, it is considered that the impact force occurs instantly, reaching an infinitely large value. The relative displacement of the colliding bodies during the impact is also assumed to be zero, and therefore, the mutual repulsion of the colliding bodies occurs only under the action of elastic deformation forces.

The interaction of the vehicle in a collision is much more complicated than described above. In the process of collision of the vehicle, contact between them occurs over large areas, and different parts enter into it, which is why the forces of interaction appear in different places. The direction and magnitude of these forces depends on the design of the contacting parts (their shape, strength, stiffness, nature of deformation), therefore the forces of interaction are different at different points of contact. Since the deformations of the vehicle upon collision can be very significant in depth, the interaction forces are variable in magnitude and direction.

The collision time is very short. There, however, the relative displacement of vehicles during this time can significantly affect their movement after a collision.

The direction of impact in a collision and the main direction of deformation of the contacting parts does not always coincide with the direction of the relative speed of the vehicle. They can coincide only in cases where the contacting areas do not slip during the impact. If slippage occurs over the entire surface, then transverse components of the interaction forces appear, causing deformations towards the lowest rigidity, and not in the direction of the longitudinal components, where the rigidity and strength of the deformable parts can be significantly higher (for example, when impacting at an angle on the side of the door of the cabin, its surface is deformed not in the direction of the impact, but in the transverse direction if the impact was sliding).

It is also impossible to assume that the impact line (the vector of the resultant impulses of the impact forces) in a collision passes through the point of initial contact. With a large area of \u200b\u200bthe deformable area, the main blow can be delivered at a considerable distance from this point when interacting with parts that are stronger and more rigid than at the point of initial contact.

The vehicle collision mechanism can be divided into three stages: the vehicle approaching before the collision, interaction upon impact, and throwing away (movement after the collision).

The first stage of the collision mechanism - the process of convergence - begins from the moment a danger arises for traffic, when to prevent an accident (or reduce the severity of the consequences), the drivers need to take the necessary measures immediately, ends at the time of the initial contact of the vehicle. At this stage, the circumstances of the incident are largely determined by the actions of its participants. In subsequent stages, events usually develop under the influence of irresistible forces that arise in accordance with the laws of mechanics. Therefore, in order to resolve issues related to the assessment of the actions of the participants in the accident from the point of view of their compliance with traffic safety requirements, it is of particular importance to establish the circumstances of the accident at its first stage (the speed and direction of the vehicle before the accident, their location along the width of the carriageway).

Some of the circumstances of the incident at the first stage cannot be established directly on the spot or by questioning witnesses. Sometimes they can be established by expert examination of the collision mechanism in subsequent stages.

The second stage of the collision mechanism - interaction between vehicles - begins from the moment of initial contact and ends at the moment when the impact of one vehicle on another stops and they begin to move freely.

Vehicle interaction in a collision depends on the type of collision, which is determined by the nature of the impact, which can be blocking and sliding. With a blocking impact, the vehicles seem to be interlocked by separate sections, and there is no slippage between them. With a sliding impact, the contacting areas are displaced relative to each other, since the speed of the vehicles is equalized.

The process of collision of a vehicle with a blocking blow can be divided into two phases.

In the first phase, the deformation of the contacting parts occurs as a result of their interaction. It ends at the moment when the relative speed of the vehicle falls to zero in the contact area and lasts for a fraction of a second. Huge impact forces, reaching tens of tons, create large decelerations (accelerations). With eccentric impacts, angular accelerations also occur. This leads to different changes in the speed and direction of the vehicle and their turn. But since the impact time is negligible, the vehicles do not have time to significantly change their position during this phase; therefore, the general direction of deformations usually almost coincides with the direction of the relative velocity.

In the second phase of the blocking blow, after the completion of the mutual penetration of the contacting sections, the vehicles move relative to each other under the influence of elastic deformation forces, as well as forces of mutual repulsion arising from an eccentric impact.

The magnitude of the impulse of elastic deformation forces is large compared to the impulse of impact forces. Therefore, with an insignificant eccentricity of the impact and deep penetration of the contacting parts, the adhesion forces between them can prevent the vehicle from separating and the second phase of the impact can end before their separation.

A sliding collision occurs in cases when the speeds in the contact areas are not equalized and, before the vehicle starts moving away from each other, the interaction occurs sequentially between their different parts located along the line of relative displacement of the contacting areas. With a sliding impact, the vehicle manages to change its relative position during the collision, which somewhat changes the direction of deformations.

During the contact time, transverse velocities of the vehicle arise, which leads to a deviation of the direction of their deformations.

A sliding impact with a small depth of mutual penetration and a high speed of relative displacement is called tangential. With such an impact, the vehicle speeds after the collision change insignificantly, but the direction of their movement will change significantly.