This thesis deals with some aspects of crack growth in the presence of cyclic loading, i.e. fatigue. The cyclic load cases studied here are primary of non-proportional mixed mode type. Under non-proportional loading the principal stress directions rotate and, generally, the ratio between the principal stresses vary. A new criterion has been presented for prediction of incipient crack path direction after changes in load from steady Mode I to non-proportional loading. The criterion is based on FE-simulations which are used to compute the actual elasto-plastic stress state in the vicinity of the crack tip. The predictions of the criterion capture several phenomena observed in the literature, which indicates that plasticity effects have to be included in a criterion for crack path predictions under non-proportional loading. The effects of Mode II overloads on subsequent Mode I crack growth have been studied relatively little in the literature. Also, the results deviates substantially. In the present thesis, this load case has been investigated in detail, both experimentally and analytically. The results show that the Mode I crack growth rate decreases after a single Mode II load, if the R-ratio is not as high as to keep the entire Mode I load cycle above the closure level. This is based on the fact, shown in this thesis, that the reduction is caused by crack closure due to tangential displacement of crack-surface irregularities. A new loading device is presented. With this device, it is possible to apply sequential loading in Mode I and Mode II in an automated way, without having to dismount the specimens. This loading device is used to study the influence of periodic Mode II loading on Mode I crack growth. The main parameters concerning the influence of periodic Mode II loading on Mode I crack growth are; (i) the Mode I R-ratio, (ii) the Mode II magnitude and (iii) the Mode II periodicity, M (number of Mode I loads for every Mode II load). The mechanisms involved are mainly RICC (Roughness-Induced Crack Closure) and a Mode II mechanism that increases the growth rate temporary at every Mode II load. Hence, the latter becomes more significant for low M-values. The higher the Mode I R-ratio the smaller is the reduction. / QC 20101004

The effect of different aging treatments on fatigue crack growth behavior of AA6013 aluminum alloy was investigated. C(T) (Compact Tension) specimens were prepared in L-T and T-L direction for fatigue crack growth tests. Samples were in T651 as received, T42 which is solution heat treated at 538 &ordm / C for 90 minutes, water quenched and aged in room temperature for 96 hours, and one group of samples were overaged at 245 &ordm / C for 12 hours after T42 condition was achieved. Hardness and conductivity measurements were achieved for all conditions after the heat treatments. Fatigue crack growth tests were performed at as received condition T651, T42 and 245 &ordm / C aged samples in laboratory air with sinusoidal loading of stress ratio R=0.1 and at a frequency of 1 Hz. The highest fatigue crack growth resistance is observed for T651 T-L and 245 &ordm / C overaged L-T condition.

Turbine engine blades are subjected to extreme conditions characterized by significant and simultaneous excursions in both stress and temperature. These conditions promote thermo-mechanical fatigue (TMF) crack growth which can significantly reduce component design life beyond that which would be predicted from isothermal/constant load amplitude results. A thorough understanding of the thermo-mechanical fatigue crack behavior in single crystal superalloys is crucial to accurately evaluate component life to ensure reliable operations without blade fracture through the use of "retirement for cause" (RFC). This research was conducted on PWA1484, a single crystal superalloy used by Pratt & Whitney for turbine blades. Initially, an isothermal constant amplitude fatigue crack growth rate database was developed, filling a void that currently exists in published literature. Through additional experimental testing, fractography, and modeling, the effects of temperature interactions, load interactions, oxidation and secondary crystallographic orientation on the fatigue crack growth rate and the underlying mechanisms responsible were determined. As is typical in published literature, an R Ratio of 0.7 displays faster crack growth when compared to R = 0.1. The effect of temperature on crack growth rate becomes more pronounced as the crack driving force increases. In addition secondary orientation and R Ratio effects on crack growth rate were shown to increase with increasing temperature. Temperature interaction testing between 649°C and 982°C showed that for both R = 0.1 and 0.7, retardation is present at larger alternating cycle blocks and acceleration is present at smaller alternating cycle blocks. This transition from acceleration to retardation occurs between 10 and 20 alternating cycles for R = 0.1 and around 20 alternating cycles for R = 0.7. Load interaction testing showed that when the crack driving force is near KIC the overload size greatly influences whether acceleration or retardation will occur at 982°C. Semi-realistic spectrum testing demonstrated the extreme sensitivity that relative loading levels play on fatigue crack growth life while also calling into question the importance of dwell times. A crack trajectory modeling approach using blade primary and secondary orientations was used to determine whether crack propagation will occur on crystallographic planes or normal to the applied load. Crack plane determination using a scanning electron microscope enabled verification of the crack trajectory modeling approach. The isothermal constant amplitude fatigue crack growth results fills a much needed void in currently available data. While the temperature and load interaction fatigue crack growth results reveal the acceleration and retardation that is present in cracks growing in single crystal turbine blade materials under TMF conditions. This research also provides a deeper understanding of the failure and deformation mechanisms responsible for crack growth during thermo-mechanical fatigue. The crack path trajectory modeling will help enable "Retirement for Cause" to be used for critical turbine engine components, a drastic improvement over the standard "safe-life" calculations while also reducing the risk of catastrophic failure due to "chunk liberation" as a function of time. Leveraging off this work there exists the possibility of developing a "local approach" to define a crack growth forcing function in single crystal superalloys.

Cracks often exist in structural members that are exposed to repeated loading, which will certainly lower the structural integrity. A crack on a structural member introduces a local flexibility which is a function of the crack depth and location. This may cause nonlinear dynamic response of the structure. In this thesis, a new method is suggested to detect and locate a crack in a structural component. The method is based on the fact that nonlinear response of a structure with a crack will be a function of the crack location and crack magnitude. The method suggested is the extension of a recently developed technique for identification of non-linearity in vibrating multi degree of freedom system. In this method, experimentally measured receptances at different forcing levels are used as input, and the existence and location of a nonlinearity are sought. In order to validate the method, simulated experimental data is used. Characteristics of a cracked beam are simulated by using experimentally obtained analytical expressions, given in the literature. The structure itself is modelled by using finite element method. Several case studies are performed to test and demonstrate the applicability, efficiency and sensitivity of the method suggested. The effect of crack depth on nonlinear system response is also studied in numerical examples.

The objective of this study is to develop crack growth analysis methods for functionally graded materials under mode I cyclic loading by using finite element technique. The study starts with the analysis of test specimens which are given in ASTM standard E399. The material properties of specimens are assumed to be changing along the thickness direction according to a presumed variation function used for the modeling of functionally graded materials. The results of the study reveal the influence of different material variation functions on the crack growth behavior. In the second part, the growth of an elliptical crack which is a common case in engineering applications is analyzed. First, mode I cycling loading is applied perpendicular to the crack plane and crack growth profiles for a certain number of cycles are obtained for homogeneous materials. Then, the code is extended for the analysis functionally graded materials. The material properties are assumed to vary as an exponential function along the major or minor axis direction of the crack. The results can be used to examine the crack profile and material constants&rsquo / influence for a certain number of cyclic loading.

No description available.

H υποβάθμιση της δομικής ακεραιότητας των αεροπορικών κατασκευών με το χρόνο και η αποτίμηση της αποτελεί ένα σημαντικό τεχνολογικό πρόβλημα της αεροναυπηγικής. Το πρόβλημα αυτό σε συνδυασμό με το ότι εξακολουθούν να χρησιμοποιούνται αεροσκάφη, τα οποία έχουν ξεπεράσει τον αρχικά σχεδιασμένο χρόνο της επιχειρησιακής τους λειτουργίας, οδήγησε τη διεθνή επιστημονική κοινότητα και την αεροπορική βιομηχανία να ασχοληθεί με το πρόβλημα του “γηράσκοντος” αεροσκάφους (aging aircraft). Το πρόβλημα της γήρανσης της δομής ενός αεροσκάφους οφείλεται κυρίως στην εμφάνιση ευρείας έκτασης βλάβης κόπωσης (wide spread fatigue damage) σε διάφορες περιοχές της κατασκευής, η οποία αυξάνει την πιθανότητα εμφάνισης καταστροφικών αστοχιών. Οι ηλωτές συνδέσεις των ελασμάτων που συνθέτουν την άτρακτο ή τις πτέρυγες ενός αεροσκάφους αποτελούν περιοχές συγκέντρωσης τάσεων και εστίες διάβρωσης με συνέπεια την εμφάνιση και εξέλιξη μικρών ρωγμών σε πολλαπλά σημεία της δομής. Η κατάσταση της ύπαρξης πολλών αλληλεπιδρουσών ρωγμών στο ίδιο δομικό στοιχείο ονομάζεται πολλαπλή βλάβη (Multiple Site Damage – MSD) και οδηγεί σε σημαντική μείωση της εναπομένουσας αντοχής του δομικού στοιχείου και σε υποβάθμιση της δομικής του ακεραιότητας. Η μελέτη του προβλήματος της πολλαπλής βλάβης και η αντιμετώπισή του αποτελεί σημαντικό πεδίο έρευνας, καθώς περιλαμβάνει πλήθος επιμέρους φαινομένων, τα οποία αλληλεπιδρούν μεταξύ τους. Τέτοια φαινόμενα είναι η έναρξη, η διάδοση και η συνένωση πολλαπλών ρωγμών, η τελική αστοχία δομικού στοιχείου σε συνθήκες πολλαπλής βλάβης, καθώς και η επίδραση περιβαλλοντικών παραγόντων όπως η διάβρωση στη συμπεριφορά των υλικών. Σκοπός της παρούσας εργασίας είναι η ανάπτυξη μιας ολοκληρωμένης μεθοδολογίας για την εκτίμηση της εμφάνισης και εξέλιξης της πολλαπλής βλάβης κόπωσης σε αεροπορικά δομικά στοιχεία, έτσι ώστε να είναι εφικτή η εκτίμηση της δομικής τους ακεραιότητας σε οποιαδήποτε στιγμή της διάρκειας λειτουργίας τους. Τα τεχνολογικά προβλήματα, που αντιμετωπίζονται στην παρούσα εργασία με ανάπτυξη πρωτότυπων μεθοδολογιών, περιλαμβάνουν: • Ανάλυση τάσεων σε πολλαπλά ρηγματωμένες κατασκευές και υπολογισμό συντελεστών έντασης τάσεων στις ρωγμές • Πρόβλεψη έναρξης και διάδοσης ρωγμών • Πρόβλεψη συνένωσης ρωγμών και εναπομένουσας αντοχής Για την ανάλυση τάσεων και τον υπολογισμό των συντελεστών έντασης τάσεων σε πολλαπλά ρηγματωμένα δομικά στοιχεία με ή χωρίς ενισχύσεις (stiffeners) αναπτύσσονται στη βάση της τεχνικής της υπο-μοντελοποίησης της μεθόδου των πεπερασμένων στοιχείων (ΠΣ) κατάλληλα υπερ-στοιχεία (super-elements) για τη μοντελοποίηση των κρίσιμων τμημάτων της κατασκευής. Η μεθοδολογία υπερ-στοιχείων επιλέγεται στην παρούσα εργασία, με σκοπό τη σημαντική μείωση του υπολογιστικού κόστους σε σχέση με τις κλασικές μεθόδους των πεπερασμένων στοιχείων, έτσι ώστε να καταστεί πρακτικά δυνατή η επίλυση του πολύπλοκου αυτού προβλήματος. Το πρόβλημα της δημιουργίας νέων ρωγμών λόγω κόπωσης σε κάποιο δομικό στοιχείο παρουσιάζει έντονα πιθανοθεωρητικό χαρακτήρα. Για την αντιμετώπισή του αναπτύσσεται μεθοδολογία σύμφωνα με την οποία η πιθανότητα να εμφανιστεί μια ρωγμή σε κάποιο σημείο μετά από ορισμένο αριθμό κύκλων φόρτισης εξαρτάται τόσο από την τάση που αναπτύσσεται στο σημείο αυτό όσο και από την πιθανότητα ύπαρξης τοπικών ατελειών του υλικού στο υπό εξέταση σημείο. Για την εφαρμογή της μεθοδολογίας χρησιμοποιούνται στατιστικά δεδομένα που προέρχονται από πειράματα κόπωσης απλών δοκιμίων. Για την εκτίμηση της εναπομένουσας αντοχής ενός πολλαπλά ρηγματωμένου δομικού στοιχείου αναπτύσσεται ένα ενεργειακό κριτήριο συνένωσης ρωγμών. Το κριτήριο βασίζεται της μεταβολής της ενέργειας παραμόρφωσης που λαμβάνει χώρα κατά τη διάρκεια της αστοχίας του υλικού που συνδέει δύο παρακείμενες ρωγμές. Τέλος, τα μοντέλα έναρξης, διάδοσης και συνένωσης ρωγμών συνδυάζονται σε μια ολοκληρωμένη μεθοδολογία, η οποία μπορεί να χρησιμοποιηθεί για την πρόβλεψη της εξέλιξης της πολλαπλής βλάβης κόπωσης. Η αποτελεσματικότητα της μεθόδου επαληθεύεται με τη βοήθεια πειραμάτων κόπωσης πολλαπλά ρηγματωμένων δοκιμίων. / Structural integrity degradation of aeronautical structures due to fatigue, as well as its assessment, represents a major problem of aeronautics. This problem, combined to the fact that numerous aircrafts that have already exceeded their initial design operational life are still in service, led the international scientific community and the aeronautical industry to the in-depth study of aging aircraft. The main problem of an aging aircraft structure is widespread fatigue damage at various areas of the structure, that increase the probability of catastrophic failures. Riveted joints of fuselage or wing panels are areas of high stress concentration and corrosion, therefore, sites susceptible to multiple cracks development. The state of multiple interacting cracks existence at the same structural element is called Multiple Site Damage (MSD) and leads to residual significant strength reduction and structural integrity degradation of the structure. Study and handling of multiple site damage problem is an important research field, as it involves a number of different interacting phenomena, such as crack initiation, propagation and link-up and final structural failure under MSD conditions, as well as the effect of environmental factors like corrosion on the material behaviour. The aim of the present work is the development of an integrated methodology for the prediction of MSD evolution at aeronautical structural elements, in order to make feasible the assessment of their structural integrity throughout their service life. The technological issues that are faced in the frame of the present work by the development of innovative methodologies are: • Stress analysis and stress intensity factors calculation of structures under MSD condition. • Crack initiation and propagation prediction. • Prediction of crack link-up and residual strength. For the stress analysis and stress intensity factor calculation of un-stiffened of stiffened structural elements suitable super-elements are developed for the simulation of crucial structural elements. The super-element methodology is based on finite element sub-structuring technique and, in the present work, is chosen in order to obtain a significant reduction of computation cost with compared to the classical finite element method, so that handling of such complex problems becomes feasible. Fatigue crack initiation at a structural element is a problem exhibiting a strongly stochastic character. A crack initiation prediction methodology is developed according to which the probability of crack initiation at a site of the structure depends on the local stress state combined to a stochastic (random) variation of the fatigue strength at every site susceptible to crack initiation. For the methodology application statistical data from simple fatigue tests are used. For the crack link-up and the residual strength estimation of a multiple cracked structural element an energy-based link-up criterion is developed. The proposed criterion is based on the strain energy variation during the failure of the ligament of two adjacent cracks. Finally, the initiation, propagation and link-up models are combined and implemented in an integrated methodology that can be used for the assessment of multiple site damage evolution. The effectiveness of the methodology is validated using suitable fatigue tests of multiple-site damaged panels.

This paper is about a genealogy of a young crack user in the city of Santa Maria, Rio Grande do Sul. In this way the notions are thought with universal pretentions which affect the young user of crack. It aims at movement production in discussions about this issue, giving emphasis to problematizing perspectives generated from educational field. This theme choice has come to since composition taken as professional experience of the researcher as the manager of Mental Health Politics of Santa Maria, and discussions and also approaches done to the Moral Affection Group Research, linked to the Post Graduation in Education Program at the Federal University of Santa Maria (UFSM), focused on violence theme and conflicts related to education. This investigation is based on genealogical perspective, grounding in Michel Foucault thoughts. The materials used were documents relative to an adolescent situation involved with the crack drug, this young L., collected in the Regional Judge of Infant and Adolescent of Santa Maria, to the health service in the city which attend users of crack, as well as news on a local newspaper which followed up his situation. As its way of genealogical analysis, these materials, along with other productions about the theme, were taken as Foucault suggests, as dispersal, a way of reducing the effects of hierarchy of research sources and their speeches. For that, they are considerated drugs and the hegemonic status of forbidden politics to that associated from legal-police and medical-psychiatrist axes. It is questioned about potency of practices to be constituted from education field as an exclusive way of putting in action a politics/pedagogy based on aspects besides prohibition. Thus, this research was upon the problematizing views of practices from hegemonic knowledge which act producing the notion of young user of crack, and it has made possible the creation of places for education rising as its autonomous field to this knowledge. / Trata-se de uma genealogia do jovem usuário de crack na cidade de Santa Maria, RS. Neste sentido são problematizadas as noções com pretensões universalizantes que afetam o jovem que usa o crack. Busca-se, ainda, produzir movimentos nas discussões sobre o assunto, dando ênfase às problematizações geradas a partir do campo educacional. A escolha pelo tema se deu a partir da composição realizada entre experiências profissionais do pesquisador como gestor da Política de Saúde Mental de Santa Maria, e as discussões e abordagens realizadas no Grupo de Pesquisa Afetos Morais, vinculado ao Programa de Pós Graduação em Educação da Universidade Federal de Santa Maria (UFSM), voltado ao tema da violência e conflitos em relação à educação. Essa investigação é baseada na perspectiva genealógica, embasada nas elaborações de Michel Foucault. Os materiais utilizados foram documentos relativos à situação de um adolescente envolvido com a droga crack, o jovem L., coletados junto ao Juizado Regional da Infância e Juventude de Santa Maria, aos serviços de saúde do município que atendem usuários de crack, bem como reportagens de um jornal de circulação local que acompanhou sua situação. Como forma de análise genealógica, estes materiais, juntamente com outras produções sobre o tema, foram abordados conforme sugere Foucault, como uma dispersão, de modo a reduzir os efeitos de hierarquização das fontes de pesquisa e seus discursos. Para tanto, são considerados as drogas e o status hegemônico da política proibicionista a elas associadas a partir dos eixos jurídico-polícial e médico-psiquiátrico. Pergunta-se pelas potências de práticas a serem constituídas a partir do campo da educação como modo de exclusivamente por em ação uma política/pedagogia baseada em aspectos para além da proibição. Assim, essa pesquisa problematizou as práticas advindas dos saberes hegemônicos que atuam produzindo a noção de jovem usuário de crack, e possibilitou a criação de espaços para que a educação emergisse como campo autônomo a esses saberes.

Made available in DSpace on 2014-12-17T14:46:59Z (GMT). No. of bitstreams: 1 JoseERJ_DISSERT.pdf: 1457023 bytes, checksum: 208c09b56664138cc540abb5ba16a86c (MD5) Previous issue date: 2013-02-27 / This study aimed to analyze the phenomenon of abdication of monitoring/treatment of crack users in a CAPS AD in Campina Grande-PB. That s an exploratory , description approach ,whose theoretical focus was historical-dialect of public politics on alcohol and drugs. The information collected was realized by using the technique of semi-structured interviews, combined with the crack users registered in CAPS AD in Campina Grande between 2007 and 2011.The material collected was subjected to thematic analysis method, obtaining the extraction of the following categories and subcategories of analysis: CATEGORY 1: Factors of abdication of monitoring/treatment in CAPS AD in Campina Grande PB with subcategory 1.1. Abdication on their own , 1.2. To take work/employment, 1.3 . Search for more intensive treatment , 1.4. Due to relapse; CATEGORY 2 : Treatment/monitoring in CAPS AD to the subcategory, 2.1. The dependence of crack and family support as reasons that led to frequent CAPS AD. CATEGORY 3: Living with crack addiction without treatment/monitoring in CAPS AD with the subcategory, 3.1. Religiosity as a therapeutic tool .The results showed a distance between priority for community treatment and the reality where there is lack of information about this kind of treatment and the admission as a solution. The discourse about the abdication of treatment of crack users make reference to the importance of family support, to the influence for the phenomenon of relapse and the affection to religious conceptions. Although the subjects recognize the qualifications of CAPS AD treatment, they try by themselves or by family influence, another ways of hospitalization. This leads us to conclude that it is necessary reflection and assessment of the work of CAPS AD. Counting on the social changes and the need of answers that the phenomenon requires / O presente estudo teve como objetivo analizar o fen?meno de desist?ncia do acompanhamento/tratamento de usu?rios de crack em um CAPS AD no munic?pio de Campina Grande-PB. Trata-se de uma pesquisa explorat?ria, descritiva e de abordagem qualitativa, cujo marco te?rico foi o enfoque hist?rico-dial?tico das pol?ticas p?blicas de aten??o em ?lcool e drogas. A coleta das informa??es foi realizada empregando-se a t?cnica de entrevista semiestruturada, aliada ao levantamento de prontu?rios dos usu?rios de crack cadastrados no CAPS AD de Campina Grande-PB no per?odo de 2007 a 2011. O material colhido em campo foi submetido ao m?todo de an?lise tem?tica, obtendo-se a extra??o das seguintes categorias e subcategorias de an?lise: CATEGORIA 1: Fatores de desist?ncia do tratamento/acompanhamento no CAPS AD de Campina Grande-PB com as subcategorias 1.1. Desist?ncias por conta pr?pria , 1.2. Para assumir trabalho/emprego, 1.3. Em busca de tratamento mais intensivo , 1.4. Devido a reca?da; CATEGORIA 2: O tratamento/acompanhamento no CAPS AD com a subcategoria 2.1 A depend?ncia do crack e o apoio da fam?lia como motivos que levavam a frequentar o CAPS AD; CATEGORIA 3: Conv?vio com a depend?ncia de crack sem tratamento / acompanhamento no CAPS AD com a subcategoria 3.1. Religiosidade como instrumento terap?utico. Os resultados evidenciaram uma dist?ncia entre a refer?ncia de prioridade para o tratamento comunit?rio e a realidade onde ainda h? desinforma??o sobre esse tipo de tratamento e a busca da interna??o como solu??o. Os discursos acerca do abandono do tratamento de usu?rios de crack fazem larga refer?ncia ? import?ncia do apoio familiar para a perman?ncia no tratamento, a influ?ncia de amigos para o fen?meno da reca?da e o apego ? concep??es religiosas. Embora os sujeitos reconhe?am a qualifica??o do CAPS AD no tratamento, tentam por iniciativa pr?pria ou por influ?ncia da fam?lia, dispositivos de interna??o. Isso nos leva a concluir que se faz necess?rio a reflex?o e avalia??o do processo de trabalho do CAPS AD ? luz das transforma??es sociais e da necessidade de respostas que o fen?meno exige

O crack é um subproduto da cocaína obtido a partir da pasta de coca acrescida do bicarbonato de sódio, sendo comercializado na forma de pequenas pedras porosas. No Brasil, o consumo de crack tem sido alvo de grande preocupação devido sua expressiva expansão em várias regiões, sendo que o aumento da prevalência do seu consumo vem sendo amplamente documentado nos últimos anos. A dependência de crack é a causa mais prevalente de internação por uso de cocaína. Há uma necessidade imediata de estudos que se direcionem para esta população. A presente pesquisa pretende demonstrar evidências capazes de contribuir para o entendimento dos mecanismos envolvidos na ação do psicotrópico crack sobre o DNA, bem como oferecer dados que auxiliem no desenvolvimento de tratamentos para pacientes usuários abusivos desta droga. Este estudo teve como objetivo avaliar o dano ao DNA e a capacidade de reparo, em 31 indivíduos usuários ativos de crack, relacionando-os com um grupo controle com 40 participantes. O trabalho foi desenvolvido através de voluntários recém internados na Clínica Marcelo Campos em São Leopoldo. Foram coletadas amostras em três momentos (internação, 48h após e ao término do tratamento) e submetidas às técnicas de micronúcleo e cometa. Dentre os resultados desta avaliação, foram evidenciados índices de dano significativamente diferentes entre os grupos nas técnicas de micronúcleos e cometa, e entre os períodos de coleta na técnica de cometa. Os valores obtidos para o índice de dano de DNA da técnica do cometa nos três momentos de avaliação revelaram uma diminuição estatisticamente significativa apenas após o término do tratamento. Em relação à utilização concomitante de outras substâncias, o consumo de tabaco ocorreu em 68% dos indivíduos, maconha em 71% e cocaína em 32%, sendo que 19% faziam uso concomitante de todas as drogas mencionadas. Houve correlação com o tempo de uso do tabaco e o índice de dano (P=0,043), MN (P=0,017) e NBP (P=0,023) em determinados momentos. O consumo de álcool ocorreu em 61,29% dos participantes, não havendo correlação estatisticamente significativa com os marcadores de dano. A idade e o tempo de utilização do crack não apresentaram associação ao índice de dano. Houve associação significativa entre o consumo de chimarrão (Ilex paraguaiensis) e MN (P= 0,045). Estudos associando o crack com dano ao DNA são, ainda, escassos. Este trabalho buscou acrescentar informações quanto ao potencial danoso desta substância. / Crack is a by-product of cocaine resulting from the addition of sodium bicarbonate to cocaine base paste, being sold in the form of small, porous rocks. In Brazil, the consumption of crack has been the subject of great concern due to its significant expansion in various regions, thus the increasing prevalence of drug use has been documented in recent years. The dependence of crack is the most prevalent cause of hospitalization due to cocaine use, supporting an immediate need for studies to target this population. This research aims to demonstrate evidence that can contribute to the understanding of the mechanisms involved in the action of psychotropic Crack on DNA, as well as provide data to assist in development of treatments for patients who are drug abusers. This study aimed to assess the damage and DNA repair capacity in 31 individuals who are active users of crack, comparing them to a control group of 40 participants. The study was conducted by volunteers newly admitted to the Clinic Marcelo Campos in São Leopoldo. Samples were collected at three time points (at admission, 48 hours latter and at the end of treatment) and subjected to the comet and micronucleus techniques. Among the results of this assessment damage indices were evident and significantly different between groups in the comet and micronucleus techniques, and between sampling periods for the comet technique. The values obtained for the rate of DNA damage in the comet technique in all three time points revealed a statistically significant decrease only after the end of treatment. Regarding the concomitant use of other substances, no significant association was found with the results. Tobacco consumption occurred in 68% of subjects, marijuana in 71% and cocaine in 32%, being 19% users of all drugs mentioned. There was a correlation over time of tobacco use and the damage index (P = 0.043), MN (P = 0.017) and NBP (P = 0.023) at certain time points.. Alcohol consumption occurred in 61.29% of the participants, there was no statistically significant correlation with markers of damage.The age and duration of use were not associated to the crack damage index. There was a significant association between the consumption of yerba mate (Ilex paraguaiensis) and MN. (P = 0.045). Studies associating the crack with DNA damage are still scarce. This study brings additional information about the potential harmful of substance.