Troksnis un vibrācija vidē - vides kvalitātes kritēriji

Vibrācija un troksnis ir vieni no visizplatītākajiem vides fizikālajiem piesārņotājiem, kas rada diskomfortu, īslaicīgus, pārejošus veselības traucējumus, kā arī var izraisīt vai veicināt dažāda veida saslimšanas, kuras atsevišķos gadījumos noved pie invaliditātes (vājdzirdība, kurlums, vibrācijas slimības IV stadija u.c.). Tiek pat uzskatīts, ka troksnis ir viena no vislielākajām mūsu gadsimta nelaimēm un viens no galvenajiem stresa izraisītājiem.Ar trokšņa un vibrācijas problēmām ir jāsastopas gan sadzīvē, gan arī darba vidē. Transporta kustība pilsētās un kokapstrādes rūpniecība, diskotēkas un tekstilrūpniecība, lidostas un ģimeniskas ķildas, dzērāju klaigāšana, skaļa mūzika daudzdzīvokļu namos - tas viss ir paaugstināta trokšņa un vibrāciju cēlonis. Ir zināms, ka apmēram 15% no visā pasaulē nodarbinātajiem ir pakļauti trokšņa kaitīgajai ietekmei. Latvijā no ik gadus pirmreizēji reģistrētajām arodslimībām aptuveni 15 līdz 30% ir dzirdes orgāna saslimšanas un apmēram tikpat daudz tiek diagnosticētas kā vibrācijas slimība. Patiesībā šo saslimšanu skaits ir lielāks, jo jāņem vērā, ka mūsu valstī vēl nav sakārtots arodekspertīzes reģistra darbs

Influence of Noise in Ambulance Vehicles on Emergency Service Personnel

Every day, noise is a ubiquitous potential hazard to our body. Importance is already dedicated early in history and still continues by steady investigations in terms of protecting the personnel in loud environment. “Worldwide, 16% of hearing loss in adults is attributed to occupational noise.” Noise-induced hearing loss (NIHL) is a sensorineural hearing loss, explained by permanent threshold shift of hearing sensitivity. NIHL not only affects the auditory system but also has psychosocial effects and is proved to have interference with general health by sleep disturbances or cardiovascular symptoms. This study aims to detect and define the sound pressure levels that ambulance service workers are exposed to during their shifts in ambulance vehicle, especially with the focus on differences during signal and non-signal use and different speed levels and determining whether the noise has hazardous character. The collection of study data is composed of two parts. The first part is the indication of noise level in the ambulance vehicle with the help of a sound level meter. The second part included a questionnaire that constituted 14 questions sent electronically. In total, 207 workers responded

An old elasticity problem in a unilateral setting

A limiting case of the Michell problem involving an elastic wedge is the unbounded solid with a semi-infinite cut, the tip of which is subjected to a concentrated force. For the limiting case, the classical solution leads to overlapping of material whenever the component of the force along the axis of symmetry is directed away from the cut, and the problem must be solved anew using unilateral boundary conditions. The required mathematics is simple, and the subject is suitable for classroom discussion. Two examples are solved explicitly, and additional exercise problems are suggested.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42668/1/10659_2004_Article_BF00042218.pd

Interface separation in the transonic range caused by a plane stress pulse

This is a continuation of the authors' investigation [1] of the localized separation between two contacting solids that is caused by an incident plane elastic wave of arbitrary form. The interface is taken as frictionless and incapable of transmitting tensile tractions. It is further assumed that the two solids have identical mechanical properties, and that the angle of incidence of the incoming wave is such that the disturbance propagates along the interface with a transonic speed. Moving dislocations are employed in the formulation and the problem is reduced to a singular integral equation with a Cauchy kernel. Specific results are worked out for an incident tensile stress pulse of a parabolic shape. An intriguing aspect of the results is that, in spite of the incident wave being continuous, the elastic fields are singular at the trailing edge of the separation zone.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23628/1/0000591.pd

An example for frictional slip progressing into a contact zone of a crack

We consider a crack in a linearly varying field of normal stress that is kept constant, and apply shearing tractions that increase with time. This leads eventually to slip progressing into the closed part of the crack. If the crack lies entirely in the compressive part of the normal stress field, the problem can be solved in closed form, and it is easy to get results also for shearing tractions that start to decrease and eventually lead to backslip.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23690/1/0000660.pd

Green's functions for planar thermoelastic contact problems -- Interior contact

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23713/1/0000685.pd

Shape of a worn slider

A slider can be expected to wear in due time to a shape that gives a uniform contact pressure and consequently uniform friction stress. Computation of the worn shape is discussed using the theory of elasticity. The results show that the trailing edge may be worn down more than the leading edge. The worn shape at a sharp corner may be either convex or concave depending on the elastic constants, the friction coefficient and the corner angle.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23185/1/0000112.pd

Authors' reply

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23292/1/0000229.pd

Effect of friction on the interface crack loaded in shear

The conventional formulation used in the past for problems involving interface cracks leads to a physical contradiction: The two sides of the crack are assumed to be free of tractions in the formulation, but the crack faces are seen to overlap after the solution is constructed. This unsatisfactory feature can be eliminated by introducing contact zones at the tips of an interface crack. The present article investigates the effect of friction in the contact zones for loads that start from zero and are increased monotonically. As an application, shear loading is considered, and the problem is reduced to a singular integral equation with a Cauchy-type kernel which is solved numerically. The results show that one of the contact zones is large and that friction affects the global nature of the stress fields. The results worked out include also the stress intensity factors, crack opening displacement, and the pressure distribution in the larger contact zone. La formulation habituelle utilisée dans le passé pour des problèmes de fissures interfaciales conduit à une contradiction physique: Les deux lèvres de la fissure doivent être libres de contraintes, mais la solution peut impliquer une interpénétration des bords. Il est possible d'éliminer cette contradiction physique en introduisant des zones de contact aux pointes de la fissure. Le présent article étudie l'effet du frottement dans les zones de contact pour des charges croissantes à partir de zero. Comme application, on considère une charge de cisaillement et le problème se réduit à une équation intégrale singulière avec un noyau de type Cauchy. Cette équation est résolue numériquement. Les résultats montrent que l'une des zones de contact est grande et que le frottement modifie l'ensemble du champ de contraintes. On a aussi obtenu les facteurs d'intensité de contraintes, l'ouverture de la fissure et la distribution du pression dans la plus grande zone de contact.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42666/1/10659_2004_Article_BF00044504.pd