How to understand external mechanical influence. External mechanical impact on the phone. An example of insurance that was not fun

Mechanical impacts include static, vibration and shock loads, linear accelerations and acoustic noise. They cause destruction due to tension, compression, bending, torsion, shearing, indentation and fatigue of the product material.

Products intended to operate under mechanical loads must be durable and resistant to impact. Products not intended to operate under conditions of mechanical loads must only be durable when exposed to them.

Rice. 2.1.

Resistance to mechanical factors is the ability of products to perform their functions and maintain their parameters within established standards during exposure to mechanical factors.

In practice, we usually deal with complex loading, in which the product is exposed to a complex of mechanical loads - static and dynamic. The nature, magnitude, direction and distribution of efforts, stresses and other factors may change over time. Without proper consideration of the entire complex of loads and their changes over time, it is impossible to correctly assess the strength properties of products. During operation, during transportation, movement and storage, products and materials are exposed to dynamic loads.

The most common factors of dynamic mechanical impact are vibration loads. The inertial forces arising from vibrations can cause stresses that exceed the strength and endurance limits of the structure. The intensity of vibration is characterized by the frequency and amplitude of vibration, as well as the magnitude of maximum acceleration. Vibrations are mechanical vibrations in the frequency range of 0.1...2000 Hz or more, displacement amplitudes of 0.001 microns...100 microns or more, acceleration amplitudes of up to 1,000 m/s 2 or more. Most of the oscillations encountered in practice have the form of a distorted sinusoid.

The parameters of linear vibration include movement, speed, acceleration, sharpness (the third derivative of movement with respect to time), force, power. The parameters of angular vibration include rotation angle, angular velocity, angular acceleration, angular sharpness, torque. The parameters of both types of vibrations also include phase, frequency and nonlinear distortion factor. The nature of vibrations, both in frequency and amplitude, can vary significantly from design to design, depending on the operating conditions of the products and other influencing factors. The greatest danger is the multiplication of vibrations that occurs at the resonant frequencies of elastic structures.

Vibration loads created by various power plants, equipment, as well as unbalanced rotating and moving parts of machines, cause structural failure of a fatigue nature, disable fastening devices, contribute to the appearance of a “microphone” effect and disrupt the settings of adjustable elements, cause short circuits and breaks in electrical circuits elements of radio-electronic and electrical devices, lead to a violation of the sealing of the blocks.

Depending on the magnitude and type of vibration loads, the degree of rigidity of the product is established and tests are carried out for vibration strength, vibration resistance and detection of structural resonances. Vibration tests use sinusoidal, random broadband, or vibration previously measured on a prototype.

Shock loads are also often encountered during the operation of modern structures, machines and devices. Mechanical shocks can be single, multiple or complex. Single and multiple impact processes can affect an object in horizontal, vertical and inclined planes. Complex shock loads impact an object in two or three mutually perpendicular planes simultaneously. Impact loads of products can be both non-periodic and periodic and can have both variable and the same degree of rigidity. The occurrence of shock loads is associated with a sharp change in acceleration, speed or direction of movement of products. Most often, in real conditions, a complex single shock process occurs, which is a combination of a simple shock pulse with superimposed oscillations. The main parameters of the impact process are acceleration, displacement, speed, and deformation of the considered point of the body under impact. Important has the form of a shock pulse. Products that receive a blow are shaken, and rapidly damping natural vibrations are excited in them. The magnitude of the overload upon impact, the nature and speed of stress propagation throughout the product are determined by the strength and duration of the impact and the nature of the change in acceleration. Impact, affecting the material and product, can lead to mechanical destruction.

Loads from linear accelerations, arising in the nodes of rotating mechanisms. The effect of centrifugal acceleration is determined in each of three mutually perpendicular directions with respect to the product. Linear accelerations change up to 10 4 m/s 2 or more.

Acoustic noise- in most cases an interfering factor that can also affect the ability of products to perform their functions. The most common noise frequencies are 125... 10000 Hz, maximum level sound pressure 200 dB or more. To take into account the impact on products of changes in noise frequency, appropriate tests are carried out with a tone of varying frequency 125... 10000 Hz. Acoustic noise has a significant effect on relatively large products. That's why semiconductor devices, microelectronics products are little susceptible to the destructive effects of sound pressure. The effect of acoustic noise on products depends on the magnitude of the force on the product, the determined sound pressure level and the area of the product. The mechanism of the destructive effects of sound pressure is similar to the destructive effects of vibration. Moreover, as a result of the action of vibration energy audio frequency in radio-electronic devices, a “microphone” effect occurs and resonance phenomena appear.

We will consider the resistance of instrumentation to mechanical influences using the example of aviation instruments and devices, since they operate under the most severe conditions of the complex influence of all types of mechanical factors.

The main sources of external dynamic influences on aircraft instrumentation (AU) are the aircraft on which it is installed and the environment. The excitation of dynamic influences from the aircraft is called kinematic, and from internal devices LA - by force. Force impacts most often result from the operation of power supply units, air conditioning devices, hydraulic systems, fuel supply, etc., i.e. electromechanical devices with reciprocating moving masses or unbalanced rotating rotors.

Mechanical impacts include: linear overloads, vibrations, shocks.

During transmission from the source to the AUV and its elements, external mechanical influences are transformed - the amplitude-frequency characteristics of vibrations, the amplitude and duration of shock pulses change; transient oscillatory processes occur that accompany the effects of long-term linear loads.

G-force is the ratio of the effective acceleration to the acceleration of gravity. Linear overloads, with the exception of short-term ones, cannot be eliminated or weakened. Therefore, the operability of structures is ensured by increasing the rigidity and strength of the elements, which, as a rule, leads to an increase in the mass of AUV structures.

AUV vibration is understood as mechanical vibrations of its elements or the structure as a whole. Vibration can be periodic or random. In turn, periodic vibration is divided into harmonic and polyharmonic, and random vibration into stationary, non-stationary, narrowband and broadband.

Vibration is usually characterized by vibration displacement, vibration velocity and vibration acceleration.

Vibration displacement during harmonic vibration is defined as

Where Z- vibration displacement amplitude; - vibration frequency.

Vibration velocity and vibration acceleration are found as a result of differentiation (5.1):

Vibration acceleration during harmonic vibration is ahead in phase of vibration displacement by an angle, vibration velocity by an angle.

Amplitudes of vibration displacement Z, vibration velocity , vibration acceleration and angular frequency of vibration are the main characteristics of harmonic vibration. However, in addition to them, harmonic vibration can be characterized by vibration overload

. (5.2)

If in (5.2) the amplitude of vibration displacement is expressed in mm, and the acceleration of gravity in , then the relationship for vibration overload can be written in the form , Where - circular vibration frequency.

Polyharmonic or complex periodic vibration can be represented as a sum of harmonic components.

Random vibration is characterized by the fact that its parameters (amplitude of vibration displacement, frequency, etc.) change randomly over time. It can be stationary and non-stationary. In the case of stationary random vibration, the mathematical expectation of vibration displacement is zero, the mathematical expectation of vibration velocity and vibration acceleration is constant. In the case of non-stationary vibrations, the statistical characteristics are not constant.

In addition to vibration, the structure may be subject to shock impacts arising during operation, transportation, installation, etc. During an impact, structural elements experience loads for a short period of time, accelerations reach large values and can lead to damage to the elements. The intensity of the impact depends on the shape, amplitude and duration of the shock pulse.

The shape of the shock pulse is determined by the dependence of shock acceleration on time (Fig. 5.1). When analyzing shock effects, the real shape of the shock pulse is replaced by a simpler one, for example, rectangular, triangular, half-sinusoidal.

The amplitude of the shock pulse is taken to be the maximum acceleration upon impact. The duration of the impact is the time interval during which the shock pulse operates.

The consequence of the impact is damped vibrations occurring in the structural elements. Therefore, in practice, there is a need to protect AUV structures from shocks and vibrations simultaneously, since in real operating conditions structures are often subjected to complex mechanical influences, which should be reflected

when designing protective equipment.

AUV structural elements are characterized by their mechanical resonant frequencies, which vary widely depending on the mass and rigidity of the fastening components. In all cases, the formation of a mechanical oscillatory system in the load field must not be allowed - this applies to circuit boards, panels, casings, mounting wires and other parts of the AUV structure.

The load field refers to the mechanical loads of the system caused by fluctuations of various frequencies and amplitudes during testing, installation, transportation and operation.

As a result of mechanical influences, reversible and irreversible changes can occur in the AUV structural elements.

Reversible changes are typical for AUV electrical and radio products, which leads to instability and deterioration in the quality of functioning of the equipment. Factors causing reversible changes can be combined into the following groups depending on the physics of the processes occurring in the structure:

Deformations in active and passive components, leading to changes in their parameters;

Violations of electrical contacts in connectors and permanent connections, causing a change in the ohmic resistance of the contacts;

Changes in the parameters of electric, magnetic and electromagnetic fields, which can lead to a violation of the conditions of electromagnetic compatibility in the structure.

Irreversible changes are characteristic of AUV structural elements, are associated with a violation of strength conditions and are manifested in mechanical destruction of the elements. Elements that are pre-loaded during assembly and electrical installation (bolts,

screws, rivets, welds with residual thermal stresses, bulk conductors with excessive tension, etc.).

Irreversible changes that occur in the structural elements of AUVs under mechanical influences include fatigue failure.

Fatigue is the process of gradual accumulation of damage in the material of a part under the influence of alternating stresses. The mechanism of this process is associated with the structural heterogeneity of the material (individual grains are not the same in shape and size, are differently oriented in space, have inclusions, structural defects). As a result of this heterogeneity, shears arise in individual unfavorably oriented grains (crystals) under variable stresses, the boundaries of which expand over time, move to other grains and, covering an increasingly wider area, develop into a fatigue crack. The fatigue strength of materials depends on the magnitude and nature of stress changes and on the number of loading cycles.

AUV structures operating under mechanical stress must meet the requirements of strength and stability. Strength (vibration and impact resistance) to mechanical factors means the ability of structures to perform functions and maintain parameter values within the limits established by standards after exposure to mechanical factors.

Resistance (vibration and impact resistance) to mechanical factors is understood as the ability of a structure to perform specified functions and maintain its parameters within the limits established by standards during exposure to mechanical factors.

Please help me figure it out. And tell me what to do in this case, the phone is not cheap. The examination conclusion suggests that the phone is completely faulty. Fesenko Nina Viktorovna (04/01/2020 at 14:03:22) Good afternoon, Anna. Very often, insurance companies either refuse to pay for property insurance or significantly underestimate it. You need to go to court at the location of the company (the only way you can get the insurance paid), but to do this, contact the company again to receive a written refusal to pay the insurance.

Warranty extension

provision of services under a certificate is possible only if these documents are available. The certificate becomes valid on the 16th day following the day of purchase.

Cases not covered by the Service Certificate in which the buyer will be denied repairs: the interface cable or data transmission kit is faulty; the portable communication device is faulty; faulty car or desktop Charger; other accessories are faulty; the rules and operating conditions have been violated (i.e.

Law Club Conference

Novosibirsk, st. Frunze, 232 and filed a claim about the occurrence of an insured event. On February 13, 2020, I received a written refusal (out. No. 53 dated February 2, 2018), which stated that “According to clause 3.2.1.8.1 special conditions insurance, mechanical damage must be understood as external influences on the item. According to points "e". Clause 3.4 of the special conditions does not constitute an insured event of damage in the form of: - scratches, chips and other cosmetic damage to the insured property that does not affect its performance. — internal breakdowns without external damage, including breakdowns resulting from manufacturer defects.

On February 3, 2018, having learned by phone about the refusal to recognize the case as insurance, I contacted the official service center Sony, where 10 days later the phone was returned to me with a letter in which the service center refuses to make warranty repair phone, due to the impossibility of doing this with broken screen. Also, on 02/13/2020 I contacted contact center VTB Insurance by phone 88001004440, where in response to my request to give me advice on a hypothetical insured event, the specialist clearly stated “that insurance under the Purchase Protection program (Advantage for equipment / portable +) implies coverage in the event of an insured event due to external mechanical impact, such as: dropped, broken, etc.” 1.

External verification

Decision in Case 2-1716

In Irkutsk, a Smartphone insurance contract was concluded. for the risk “Fire, explosion, lightning strike, exposure to liquid, natural disaster, assault, robbery, hooliganism, theft, exposure to foreign objects, exposure as a result of an accident,” the insured amount was. rub. The insurance premium was paid by the plaintiff in the amount. R. An insured event occurred during the validity period of the insurance policy. The plaintiff was getting off the bus, she was pushed and the phone fell onto the roadway, and a minibus was driving over it as it was leaving the stop.

The insurance company refused to pay the plaintiff an insurance claim, indicating that external mechanical damage was not covered by the insurance policy. By concluding an insurance contract, the plaintiff believed that she was insuring her phone against all risks, incl.

Mechanical impacts are usually divided into three classes: a) linear overloads; b) vibration effects; c) shock impacts.

Linear overloads

Linear overloads are kinematic impacts that occur during accelerated movement of a source. Significant linear overloads occur on transport vehicles, especially on aircraft, with increasing speed, braking, and also during various maneuvers of the aircraft (turn, turn).

Rice. 2. Law of linear overload change

Rice. 3. Characteristics of harmonic kinematic influences

The main characteristics of linear overloads are constant acceleration (Fig. 2) and the maximum rate of increase in acceleration, called sharpness or acceleration gradient.

Vibration effects

Kinematic and force vibration effects are oscillatory processes. Force impacts are characterized by functions of time, expressing the components of forces or moments of force acting on an object, or kinematic impacts are characterized by accelerations of source points associated with the object by their velocities and displacements

Vibration effects are divided into stationary and non-stationary. The simplest type of stationary vibration effect is harmonic:

where is the force or kinematic effect.

A common source of harmonic influences are unbalanced parts of mechanisms that rotate or move translationally according to a harmonic law. In some cases, the amplitude and frequency of the harmonic effect can take on different values depending on the operating mode of the source; for example, a motor rotor may have different rotation speeds under different operating conditions. Force impacts on the engine body caused by unbalance of the rotor will have a frequency equal to the angular velocity, and their amplitude (in the case of a rigid rotor) is proportional to the square of the angular velocity.

Various technical objects are subjected to harmonic influences during vibration tests. Harmonic force effects are created

mechanical, electromagnetic or electrodynamic vibrators, and harmonic kinematic effects - mechanical, electrodynamic or hydraulic vibration stands. The comparative simplicity of devices that reproduce harmonic influences determines the widespread use of harmonic vibration tests. At the same time, regulatory documents determine the range of changes in the frequency of vibration effects and the value of amplitudes in this frequency range. The graph defining the harmonic kinematic action (Fig. 3) is usually plotted in logarithmic coordinates; in this case, power-law dependences of amplitude on frequency are depicted by straight segments.

On the kinematic characteristics of harmonic kotebanny and their complex representation, see vol. 1, ch. I, paragraph 4.

In machines containing cyclic mechanisms, during steady motion periodic mechanical impacts occur

Often in such systems it is possible to neglect the influence of all harmonics except one and consider the influence to be harmonic. This is possible in cases where one of the harmonics (usually the first) prevails over the others or when one of the harmonics of the influence is resonant for a given object.

In the spectral analysis of periodic processes (see Vol. 1, Chapter I, paragraph 4), we can limit ourselves to determining the Fourier coefficients for those harmonics of the influence whose frequencies fall within the region of the spectrum of the object’s natural frequencies.

At many modern technical objects, stationary vibration impacts are not periodic; the law of their change over time is irregular, chaotic. The main reasons for this randomness are the existence of a large number of independent sources of vibration and the irregularity of some physical processes that cause the appearance of vibration effects (for example, combustion processes in a jet engine, aerodynamic forces during flow turbulence, etc.).

In many cases, a polyharmonic function of time can serve as a fairly adequate description of chaotic vibration

(it is assumed that there is no constant component in the vibration effect), In particular, in this way the sum of a finite number of periodic processes can be approximately represented

If among the frequencies there are incommensurable ones, then this sum will describe an almost periodic process (see Vol. 1, Chapter I, paragraph 5). A polyharmonic process with incommensurate frequencies adequately describes the vibration effect excited by several independent sources, since in this case changes in phase shifts (“phase advance”) between individual components are modeled.

Non-stationary vibration effects are most often excited by transient processes occurring in the sources. For example, the force impact on the housing of an engine with an unbalanced rotor that occurs during acceleration can be approximately described by the expression

where is the law of change in the angular velocity of the rotor.

When braking an aircraft that has landed, vibrations occur, causing non-stationary vibration effects on the equipment and crew of the aircraft.

The difficulty of representing vibration effects in the form of explicit functions of time has led to the widespread use of various characteristics, reflecting the most essential properties of these processes. Characteristics of the vibration process are called functionals that depend on certain parameters

The joint characteristics of the processes are determined in a similar way

Determining the characteristics of processes from records of their implementations is the task of vibration analysis (see Vol. 5).

Fourier transform. The Fourier transform of an absolutely integrable process over an infinite interval is a complex function with:

Real functions

are called cosine transform and sine transform, respectively. For processes (1) - (4) integral (8) diverges; for these processes, the Fourier transform is understood as the function

Here the functional is equal to the average value of the function in parentheses on an infinite interval;

For the harmonic function

For a batch process (2)

For a polyharmonic process (3)

In what follows we also use the function

which is a Fourier transform on a finite time interval. For a polyharmonic process (3)

The function is shown in Fig. 4.

Spectral representations (8) and (10) cannot always be used to adequately describe mechanical effects. The first of them is suitable only for absolutely integrable, i.e., practically, for damped processes; when using the second, information about any terms of the influence that do not consist of harmonic components is lost. For example, for process (5) transformation (10) is identically equal to zero. For this reason, another form of spectral representation is used.

Rice. 4. Function

Real function

is called the amplitude spectrum of the process Function and is related by the Parseval formula:

where is called the process energy Expression

can be considered as the energy of some process for which the Fourier transform is defined as follows:

The process is obtained by passing the process through an ideal bandpass filter, the frequency response of which is shown in Fig. 5, and (16) is the energy of that part of the process whose spectrum lies in the passband of this filter.

Rice. 5. Frequency response ideal notch filter

Magnitude

is called the dense spectral energy of process x at frequency

For an undamped vibration effect, transformation (8), and therefore the amplitude spectrum, do not exist. However, for any process limited in modulus, a finite value also exists

which is called the power of the process. For power, the following relation is valid:

in which is determined by (12).

Magnitude

called power spectral density, or in short, process spectral density

Spectral density exists and is limited for any undamped limited process that does not contain harmonic components. For a harmonic process (1)

where is the delta function.

Relationship between the RMS value of a process and its spectral density

If two processes are bounded in the mean square, then

is called their mutual spectral density. For we get

Correlation transformation. Function

called correlation transformation or convolution of the process For a polyharmonic process (3)

Thus, during the correlation transformation, as well as during the transition to the spectral density of the process, information about the phases of individual

harmonic components. For a process that does not contain harmonic components,

The correlation transformation and the spectral density of the process are related to each other by the Fourier transform:

When reaches the maximum value!

Distribution function and distribution density. The mechanical impact distribution function is the relative duration of time intervals during which

where is the unit function, Derivative

is called the distribution density of the process. If there is some bounded function, then

where both the smallest and largest values

Of greatest practical interest are the moment characteristics of vibration impacts, which are the average values of integer powers from

Based on the previous assumption

The distribution function of the process coincides with the distribution function of a random variable - the value of a random choice (if a random variable whose values are uniformly distributed over an infinite interval). Therefore, it has all the properties of the distribution density of a random variable. In particular,

The distribution density of the polyharmonic process (3) is a function and does not depend on frequencies. If all

distributions do not depend on phases. In this case, for process (3)

Here is the Bessel function of zero order,

The first moments of a polyharmonic process with incommensurable frequencies

Here 2 means the sum of those terms for which they are different. Joint process distribution function and

represents the relative duration of time intervals during which the inequalities are simultaneously satisfied

Joint distribution density

When studying vibration effects, the joint distribution density of the process and its derivative is of greatest interest

Through expresses such an important characteristic of the vibration effect as the average number of level crossings per unit of time:

This characteristic is directly related to the study of fatigue phenomena in an object. Magnitude

is called the average frequency of vibration exposure.

The distribution density of a large number of independent vibration impacts, comparable in level, can be considered close to the Gaussian normal law:

where is the mean value of the square Average frequency of the normal process

The closeness of the sum of a large number of independent vibration influences (for example, a polyharmonic process with a large number of harmonics excited by independent sources) to the normal process is not ensured at large values (in the “tails” of the distribution law).

The range in which the frequencies of polyharmonic influences occurring in modern technical objects are located is very wide. Polyharmonic influences covering a range exceeding several octaves are called broadband; if the width of the range is small compared to the average frequency of the process, the effect is called narrowband. Narrowband influences manifest themselves in the form of beats (see Vol. 1, Chapter I, paragraph 5).

When solving vibration protection problems, taking into account the width of the mechanical impact band is of paramount importance. In particular, the choice of a dynamic model (calculation scheme) of the protected object depends on the broadband impact; it must be selected in such a way that the natural frequencies of the object located in the impact spectrum band are taken into account.

High-frequency vibration impacts can be transmitted to an object not only through elements of its mechanical connections with the source, but also through environment(air, water). Such influences, called acoustic ones, are especially intense on modern jet aircraft. The intensity of acoustic impacts is characterized by the magnitude of the acoustic field pressure; relative efficiency is measured in decibels. The relationship between absolute and relative intensities is expressed by the formula

where pressure, relative pressure, threshold pressure, the corresponding one is usually taken

Approximate values of the amplitudes of individual harmonics of polyharmonic kinematic influences lying in different frequency ranges, the following:

Random vibration impacts. The characteristics of mechanical vibration effects necessary for the calculation of intrusion protection systems are determined either by calculation or by direct measurements under natural conditions. In both cases, a significant role is played by random factors, the influence of which cannot be predetermined in advance: scatter of source and object parameters, differences in source operating modes, etc. Impossibility of accurately taking into account all

(see scan)

Continuation of the table. 1. (see scan)

factors influencing the nature of vibration impacts leads to the advisability of describing them as random processes and using, when calculating vibration protection systems, the averaged characteristics of vibration impacts, obtained by averaging the characteristics discussed above over recorded in situ or theoretically calculated implementations (see Vol. 1, Chapter XVII , paragraphs 1-3).

When representing vibration effects stochastically, one should be careful about the assumption that the process is ergodic (see vol. 1, p. 272). The implementation of vibration impact obtained at a separate technical object cannot, for example, be considered the implementation of an ergodic process, since it does not contain information about the spread of parameters characteristic of many objects of the same design and in the same operating modes.

Impact.

Shocks are short-term mechanical impacts, the maximum values of which are very large.

A function that expresses the dependence of force, moment of force or acceleration during an impact on time is called the shape of the impact. The main characteristics of the shape are the duration of the impact and its amplitude - the maximum value of the mechanical impact upon impact.

Kinematic shock impacts occur when there are sudden changes in the growth of the source motion (for example, when landing an aircraft, launching a rocket, running a car wheel into a deep pothole, etc.). Often these phenomena are accompanied by the occurrence of vibrations in the source structure and the excitation of vibration effects.

In some cases, the impact action can be considered as a classical impact, which is reduced to an “instantaneous” change in the speed of movement of the source or to the application of “instantaneous” forces and moments. In these cases

where is the increment of speed, impulse of force or moment of force during the impact. The use of such a representation is permissible only in cases where the duration of the impact is significantly less than the shortest period natural vibrations object. In other cases, it is necessary to take into account the shape of the impact, which is usually determined by direct measurements under natural conditions.

Kinematic impact impacts are divided into impacts with and without speed increments. Impacts without speed increments are distinguished by the fact that the speed of the source at the end of the impact is equal to its speed before the impact. They occur during explosions, earthquakes, etc. Often such an impact is close in nature to non-stationary vibration.

Impact impacts can be described by the characteristics (8) and (14) discussed above. Table 1 shows the amplitude spectra of impact impacts of various shapes,

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