H.J. Schindler

Determination of residual stress distributions from measured stress intensity factors

If a crack or machined cut is introduced in a body that contains residual stresses, the latter are released at the newly created surface and cause the stress field to be rearranged in the entire body. From the change of stress due to progressive cutting as measured at any location, it is possible to calculate the stress that acted alogn the corresponding axis in the initial, uncracked state

Chronische Myoarthropathien des Kausystems

ZusammenfassungNach den Daten der Dritten Deutschen Mundgesundheitsstudie (1999) liegt die Prävalenz schmerzhafter Myoarthropathien des Kausystems (MAP) in Deutschland bei ca. 5%. Obwohl eine umfassende gesundheitsökonomische Kosten-Nutzen-Analyse weiterhin aussteht, können die Gesundheitsausgaben für MAP-Patienten beträchtlich sein. Die mit chronischen MAP in Zusammenhang stehenden ätiologischen bzw. pathophysiologischen Faktoren sind zum größten Teil wenig bekannt. Es liegen jedoch Hinweise für verschiedene (patho)physiologische Mechanismen vor, die mit der Entstehung und Aufrechterhaltung von chronischen MAP in Zusammenhang gebracht werden können (z.xa0B. Störungen der zentralen Reizverarbeitung, psychosoziale Faktoren, hormonelle Einflüsse u.xa0a.). Hohe Evidenzstärken sind derzeit für folgende Therapieverfahren vorhanden: intraokklusale Schienen (Stabilisierungsschienen), Clonazepam, Diazepam, Meprobamat, EMG-Biofeedback, multimodale Behandlungsformen (kombinierte somatisch-psychologische Schmerztherapie).AbstractAccording to the 3rd German Oral Health Study (1999), the prevalence of painful temporomandibular disorders (TMDs) is about 5%. Although limited information about the magnitude of utilization of health care services and expenses for health care in temporomandibular pain patients is available, the financial burden of affected individuals may be considerable. The etiology and pathophysiology of chronic TMDs is still obscure. However, certain (patho)physiological mechanisms may be associated with the genesis and perpetuation of these musculoskeletal facial pains (e.xa0g. disturbances in central nervous system processing; psychosocial factors; hormonal influences). Strong scientific evidence from the dental/medical literature is currently available for the following forms of TMD treatment and management: occlusal appliances (stabilization appliance), clonazepam, diazepam, meprobamate, EMG biofeedback, multimodal approaches (somatic and psychological pain management).

Path of a crack in a beam due to dynamic flexural fracture

This paper discusses some theoretical investigations of the path followed by a crack which is produced by applying a sufficiently large static bending moment to an elastic beam. It has been observed experimentally that this path does not, in general, correspond to the shortest distance across the beam, i.e. a straight line perpendicular to the beam axis. Quite often as the path approaches the opposite face of the beam it turns and runs almost parallel to the beam axis. Two aspects of this behavior are theoretically explained: first the initial deviation from the straight line, which obviously is a problem of path-stability, and second the ability of the crack to propagate afterwards more or less perpendicular to the initial direction. Path-stability is discussed by a criterion resulting from a calculation of the direction of maximum released energy during crack-propagation. The subsequent stage of crack-propagation in axial direction is discussed by applying the standard propagation criterion of maximum hoop-stress.RésuméOn discute de recherches théoriques sur le chemin parcouru par une fissure produite par lapplication à une poutre élastique dun moment statique de flexion suffisamment grand.Les observations expérimentales ont établi que ce dernier, en général, ne correspond pas à la plus courte distance dans la poutre, à savoir une ligne droite, perpendiculaire à son axe. Le plus souvent, lorsque la fissure sapproche de la face opposée à celle de son démarrage, son chemin sincurve et se développe parallèlement à laxe de la poutre. On peut expliquer par la théorie deux aspects de ce comportement: dune part, la déviation originelle de la ligne droite, qui est à lévidence un problème de stabilité du parcours, et, dautre part, la possibilité pour la fissure de se propager ensuite plus ou moins perpendiculairement à la direction initiale.La stabilité du parcours de la fissure est discutée à laide dun critère établi par un calcul de la direction dans laquelle lénergie libérée passe par un maximum au cours de la propagation de la fissure. Le stade ultérieur de propagation dans la direction parallèle à laxe de la poutre est discuté par application du critère standard de propagation basé sur la contrainte maximum de membrane.

Chronic temporomandibular disorders

ZusammenfassungNach den Daten der Dritten Deutschen Mundgesundheitsstudie (1999) liegt die Prävalenz schmerzhafter Myoarthropathien des Kausystems (MAP) in Deutschland bei ca. 5%. Obwohl eine umfassende gesundheitsökonomische Kosten-Nutzen-Analyse weiterhin aussteht, können die Gesundheitsausgaben für MAP-Patienten beträchtlich sein. Die mit chronischen MAP in Zusammenhang stehenden ätiologischen bzw. pathophysiologischen Faktoren sind zum größten Teil wenig bekannt. Es liegen jedoch Hinweise für verschiedene (patho)physiologische Mechanismen vor, die mit der Entstehung und Aufrechterhaltung von chronischen MAP in Zusammenhang gebracht werden können (z.xa0B. Störungen der zentralen Reizverarbeitung, psychosoziale Faktoren, hormonelle Einflüsse u.xa0a.). Hohe Evidenzstärken sind derzeit für folgende Therapieverfahren vorhanden: intraokklusale Schienen (Stabilisierungsschienen), Clonazepam, Diazepam, Meprobamat, EMG-Biofeedback, multimodale Behandlungsformen (kombinierte somatisch-psychologische Schmerztherapie).AbstractAccording to the 3rd German Oral Health Study (1999), the prevalence of painful temporomandibular disorders (TMDs) is about 5%. Although limited information about the magnitude of utilization of health care services and expenses for health care in temporomandibular pain patients is available, the financial burden of affected individuals may be considerable. The etiology and pathophysiology of chronic TMDs is still obscure. However, certain (patho)physiological mechanisms may be associated with the genesis and perpetuation of these musculoskeletal facial pains (e.xa0g. disturbances in central nervous system processing; psychosocial factors; hormonal influences). Strong scientific evidence from the dental/medical literature is currently available for the following forms of TMD treatment and management: occlusal appliances (stabilization appliance), clonazepam, diazepam, meprobamate, EMG biofeedback, multimodal approaches (somatic and psychological pain management).

A closer look at estimation of fracture toughness from Charpy V-notch tests

Abstract Although it is well known that the adequate parameters to characterise the toughness of materials are those according to the theory of fracture mechanics, the classical Charpy fracture energy is still often used in testing practice. Many efforts have been made to correlate these two types of toughness parameters with each other. In many cases these correlations give no satisfying results. In this paper it is investigated under what circumstances such correlation can exist and what type they are of. It is shown—from a theoretical point of view—that correlations are restricted to certain families of materials, i.e. that there are no general applicable correlation formulas. For those purposes the standard Charpy tests have to be replaced by instrumented tests on sharp notched or pre-cracked specimens.

Myalgie der Kiefermuskulatur

Masticatory muscle pain can be regarded as a regional manifestation of musculoskeletal disorders similar to those observed in other body regions. Along with temporomandibular joint pain and some painless disturbances related to mandibular mobility they are subsumed under the term temporomandibular disorders (TMD). Masticatory muscle pain is assumed to be associated with a variety of biophysiological risk factors. Valid diagnostic instruments make it possible to differentiate between the various TMD subgroups. In most cases, masticatory muscle pain can be treated/managed successfully. In a considerable number of patients, however, the pain persists over a long period of time despite therapeutic interventions. Understanding of the underlying neurobiological background of acute and chronic pain may help in therapeutic decision-making and evaluation of the therapeutic effects.ZusammenfassungKiefermuskelschmerzen können als regionale Manifestation muskuloskelettaler Beschwerden betrachtet werden, wie sie in ähnlicher Form auch in anderen Körperregionen zu beobachten sind. Zusammen mit den Kiefergelenkschmerzen und nicht schmerzhaften Störungen der Unterkieferbeweglichkeit werden sie unter dem Begriff „kraniomandibuläre Dysfunktion“ (CMD) zusammengefasst. Eine Reihe von biophysikalischen Risikofaktoren ist mit diesem Beschwerdebild assoziiert. Valide Diagnoseinstrumente ermöglichen die therapeutisch relevante Differenzierung der verschiedenen CMD-Subgruppen. Der weitaus überwiegende Teil der Kiefermuskelschmerzen ist gut behandelbar. Bei einem nicht unerheblichen Anteil der Patienten persistieren die Muskelschmerzen jedoch trotz therapeutischer Maßnahmen. Die Kenntnis der zugrunde liegenden neurobiologischen Hintergründe akuter und chronischer Schmerzen hilft bei der Wahl angemessener Therapien und bei der Abschätzung des Therapieerfolgs.AbstractMasticatory muscle pain can be regarded as a regional manifestation of musculoskeletal disorders similar to those observed in other body regions. Along with temporomandibular joint pain and some painless disturbances related to mandibular mobility they are subsumed under the term temporomandibular disorders (TMD). Masticatory muscle pain is assumed to be associated with a variety of biophysiological risk factors. Valid diagnostic instruments make it possible to differentiate between the various TMD subgroups. In most cases, masticatory muscle pain can be treated/managed successfully. In a considerable number of patients, however, the pain persists over a long period of time despite therapeutic interventions. Understanding of the underlying neurobiological background of acute and chronic pain may help in therapeutic decision-making and evaluation of the therapeutic effects.

On the effect of notch radius and local friction on the mode I and mode II fracture toughness of a high-strength steel

Abstract This paper reports on the results of an experimental and analytical investigation on the mode I and mode II fracture mechanics behaviour of a high-strength steel. The aim was to identify the effect of crack tip geometry and loading system on the loading capacity of the material. Notched as well as pre-cracked single edge notched specimens were loaded in symmetric and anti-symmetric bending. The experimental results show that crack tip and loading parameters have a significant influence on the apparent critical fracture toughness values. The influence of a finite notch radius on the mode I and mode II fracture toughness is quantified by a J -integral analysis which indicates that for both loading systems crack initiation can be estimated by a local strain energy density criterion. A weight function analysis of the mode II loading shows that crack tip shielding due to contact between the crack faces becomes important if the distance from the first support roller to the crack plane is less than the thickness of the specimen. This result helps to explain the large scatter which is present in one of the experimental loading configurations.

Kiefermuskelschmerz – Neurobiologische Grundlagen

ZusammenfassungDie Kiefermuskulatur unterscheidet sich durch ihre morphologischen, histochemischen und elektrophysikalischen Eigenschaften sowie durch ihre heterogene Aktivierbarkeit deutlich von der übrigen Körpermuskulatur. Unterschiedliche Typen von Muskelschmerz prägen das klinische Bild des anhaltenden Kiefermuskelschmerzes: eine mehr durch periphere Überlastung charakterisierbare und eine eher durch neuronale Dysfunktionen auf zentralnervöser Ebene erklärbare Form. Biomechanische Risikofaktoren scheinen v. a. für den erstgenannten Typ von wesentlicher Bedeutung zu sein. Konzepte, die zur Aufrechterhaltung des Schmerzes eine chronische Überaktivierung des gesamten lädierten Muskels annehmen, sind nach aktuellem Kenntnisstand allerdings unzutreffend, da die typische Reaktion des schmerzhaften Muskels in einer Hemmung der Aktivität besteht. Vorstellungen, die von einer differenzierten Überlastung diskreter intramuskulärer Regionen ausgehen, können hier plausiblere Erklärung liefern. Diskutiert werden die möglichen Zusammenhänge von funktionellen und strukturellen neuroplastischen Veränderungen und der zweiten Form des chronischen Muskelschmerzes, wie er z. B. durch das Fibromyalgie-Syndrom repräsentiert wird.AbstractThe masticatory muscles show morphologic, histochemical, electrophysical, and functional features that differ from the other muscles of the body. At least two kinds of masticatory muscle pain should be distinguished: A local pain associated with peripheral mechanical overuse, and a pain associated with changes in the central nociceptive system. Biomechanical factors appear to be important for the first type of muscle pain. Since the typical reaction of a painful muscle consists of inhibition of its activity, traditional concepts that postulate the maintenance of the pain by chronic overuse of the whole muscle are not supported by the current literature. Instead, differential overuse of discrete intramuscular regions appear to provide a more plausible explanation. On the other hand, the possible relationships between functional and structural neuroplastic changes and the second form of chronic muscle pain (e.g., fibromyalgia) still remain speculative.

Size effects on fracture toughness of brittle materials

The purpose of the present investigation was to explore this behaviour theoretically by using simple analytical models, aiming at closed form mathematical relations for its theoretical description

Multiple fractures produced by the bending of brittle beams

Abstract This paper describes experiments where the bending of beams results in two or more fractures being formed, apparently simultaneously. This is explained in terms of the stress waves emitted by the initial fracture process. It is shown that three separate types of secondary fracture may occur as a result of the interaction between the stress pulses produced by the initial fracture and the loading stresses already present in the beam. In treating these problems it has been found helpful to use an analytical solution for the bending wave propagated when a semi-infinite beam, which is subjected to a constant bending moment, is suddenly unloaded at the free end. In modelling the longitudinal stress pulse produced by the fracture we have used a simplified model which assumes that the forcing function on the fracture plane is a force field equal to the resultant force acting on the unbroken portion of the fracture surface prior to the onset of fracture.