| 1. |
- Alfredsson, Svante
(author)
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Constitutive Behaviour and Fracture of Adhesive Layers : Inverse Methods and Energetic Balance
- 2004
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Doctoral thesis (other academic/artistic)abstract
- In the automobile industry, current demands on reduced emissions with maintained or even increased crash worthiness, forces the industry to seek weight-reducing designs. The possibility to use lightweight materials is obviously attractive. At joints, these lightweight materials have to be connected to high-strength or low-cost materials. In this context adhesive joining can provide a flexible solution. The method adds little weight to the structure, it allows for material combinations that are not possible to weld, and it provides increased stiffness to the structure as compared to the conventional spot-welding procedure. Moreover, electrolytic isolation of the multi-material joints is achieved. In this thesis, experimental methods are developed to determine the complete stress-deformation relation for an adhesive layer loaded in shear. Generally, the stress distribution is non-uniform in the test geometries used. Evaluation of experiments is performed using an inverse method. The idea is to measure the energy release rate as a function of the crack tip deformation. The stress-deformation relation is obtained by a subsequent differentiation. The method is shown to be capable of capturing the complete stress-deformation relation under stable loading conditions. A method to accurately determine the energy release rate is needed for the inverse method to be successful. A closed form expression for the energy release rate of the end-notch flexure adhesive joint specimen (ENF) is derived in this thesis. An approximate formula containing measurable quantities is also given. It is shown that both the applied load and the crack tip deformation are needed to determine the instantaneous value of the energy release rate of the ENF-specimen. Experimental results show that the influence of the crack tip deformation can be substantial. An alternative specimen is also analysed theoretically. An initial theoretical study on mixed mode fracture of adhesive layers is also given in this thesis. A detailed comparison is made of the mode-mixity obtained using two different, frequently used mechanical models; the beam/adhesive layer model, and the continuum model, i.e. a model neglecting the presence of the adhesive layer. It is tempting to assume that the two methods would produce similar results for the case of a thin adhesive layer. However, this is only the case for geometries which are materially and geometrically symmetric with respect to the adhesive layer. For asymmetric joints, on the other hand, the two models are found to predict fundamentally different values of the mode-mixity. Moreover, the mode-mixity of the beam/adhesive layer model is found to depend highly on the relative stiffness of the adherends and the adhesive layer. This dependency is found to be quantified through two parameters.
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| 2. |
- Andersson, Tobias
(author)
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Mechanical Behaviour of Adhesive Layers : Methods to Extract Peel and Mixed Mode Properties
- 2006
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Doctoral thesis (other academic/artistic)abstract
- Mechanical Behaviour of Adhesive Layers Methods to Extract Peel and Mixed Mode Properties TOBIAS ANDERSSON Department of Applied Mechanics Chalmers University of Technology ABSTRACT This thesis is concerned with methods to extract material properties of thin adhesive layers loaded in peel and in mixed mode. The first part of the thesis is devoted to an experimental method to determine the complete stress-elongation relation (or cohesive law) for an adhesive layer loaded in peel using the DCB-specimen. The method is based on the concept of equilibrium of the energetic forces acting on the specimen. Two sources of energetic forces are identified: the start of the adhesive layer and the positions of the two acting loads. By use of the concept of equilibrium of energetic forces, it is possible to measure the energy release rate of the adhesive layer instantaneously during an experiment. The complete stress-elongation relation is found to be the derivative of the energy release rate with respect to the elongation of the adhesive layer at its start. By this procedure, an effective property of the adhesive layer is measured. The validity of the approach is investigated by experiments where the adherends deform 1) elastically and 2) plastically. It is found that a unique stress-elongation is obtained when the adherends deform elastically. The same relation cannot be used to predict the experiments where the adherends deform plastically indicating that the approach has limited applicability. The second part of the thesis is concerned with the development of a mesomechanical finite element model of a thin adhesive layer loaded in mixed mode. The model is calibrated to previously performed experiments. In these, the adhesive layer is loaded in monotonically increasing peel or shear. An in situ SEM-study is also performed and used to guide the modelling and calibration. The purpose of the mesomechanical finite element model is to facilitate the development of constitutive laws for adhesive layers. The modelling is based on Xu and Needleman’s method where all continuum finite-elements are surrounded by interface elements that allow for the development of micro cracks. Thus, this enables the modelling of the entire process of degradation and fracture of the adhesive layer. A genetic algorithm is developed for the calibration. The simulations are shown to be in reasonably good agreement with the experiments. Keywords: adhesive layer, stress-elongation relation, J-integral, energetic force, experimental method, RVE, interface elements, genetic algorithm
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| 3. |
- Bagland, Véronique, et al.
(author)
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Stationary states for the noncutoff Kac equation with a Gaussian thermostat
- 2007
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In: Nonlinearity. - : Institute of Physics Publishing (IOPP). - 0951-7715 .- 1361-6544. ; 20:3, s. 583-604
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Journal article (peer-reviewed)abstract
- We study the stationary states of a Kac equation with a Gaussian thermostat in the case of a noncutoff cross section. We investigate the existence, smoothness and uniqueness of the stationary states. The theoretical results are illustrated by some numerical simulations.
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| 4. |
- Behboudi, Afrouz, 1967, et al.
(author)
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Evolutionary aspects of the genomic organization of rat chromosome 10.
- 2002
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In: Cytogenetic and genome research. - : S. Karger. - 1424-8581 .- 1424-859X. ; 96:1-4, s. 52-9
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Journal article (peer-reviewed)abstract
- Using FISH and RH mapping a chromosomal map of rat chromosome 10 (RNO10) was constructed. Our mapping data were complemented by other published data and the final map was compared to maps of mouse and human chromosomes. RNO10 contained segments homologous to mouse chromosomes (MMU) 11, 16 and 17, with evolutionary breakpoints between the three segments situated in the proximal part of RNO10. Near one of these breakpoints (between MMU17 and 11) we found evidence for an inversion ancestral to the mouse that was not ancestral to the condition in the rat. Within each of the chromosome segments identified, the gene order appeared to be largely conserved. This conservation was particularly clear in the long MMU11-homologous segment. RNO10 also contained segments homologous to three human chromosomes (HSA5, 16, 17). However, within each segment of conserved synteny were signs of more extensive rearrangements. At least 13 different evolutionary breakpoints were indicated in the rat-human comparison. In contrast to what was found between rat and mouse, the rat-human evolutionary breaks were distributed along the entire length of RNO10.
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| 5. |
- Bergh, Ingrid, et al.
(author)
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An application of pain rating scales in geriatric patients
- 2000
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In: Aging Clinical and Experimental Research. - : Elsevier. - 1594-0667 .- 1720-8319. ; 12:5, s. 380-7
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Journal article (peer-reviewed)abstract
- This study examined the applicability of three different pain rating scales, the Visual Analogue Scale (VAS), the Graphic Rating Scale (GRS) and the Numeric Rating Scale (NRS), in geriatric patients. Data collection was performed in a geriatric clinic at a university hospital. A structured interview was conducted with 167 patients (mean age = 80.5 years). Patients rated their current experience of pain twice with a 5-minute pause in-between on the VAS, GRS and NRS, and were then asked if they experienced pain, ache or hurt (PAH) or other symptoms. The correlations were high and significant both between the ratings of the VAS, GRS and NRS (r = 0.78-0.92; p < 0.001) (alternative-forms reliability), and between the test and retesting (r = 0.75-r = 0.83; p < 0.001) (test-retest reliability). A logistic regression analysis showed that the probability to accomplish a rating on the pain scales decreased with advancing age of the patient, and this was especially marked for the VAS. The probability of agreement between the patients' ratings of pain and the verbal report of PAH tended to decrease with advancing age; this was especially so for the VAS. Patients who verbally denied PAH but reported pain on the scales rated it significant lower (p < 0.001) than those who verbally reported PAH and rated the pain as well. Eighteen percent of patients who denied pain but rated a pain experience verbally expressed suffering or distress. The study suggests that pain rating scales such as the VAS, GRS and NRS can be used to evaluate pain experience in geriatric patients. However, agreement between verbally expressed experience of PAH, and the rated experience of pain tended to decrease with advancing age. This indicates that the pain-evaluating process will be substantially improved by an additional penetration supported by a wide variety of expression of hurt, ache, pain, discomfort and distress.
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| 6. |
- Bergh, Ingrid, 1956, et al.
(author)
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Assessing pain and pain relief in geriatric patients with non-pathological fractures with different rating scales.
- 2001
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In: Aging (Milan, Italy). - : Kurtis. - 0394-9532. ; 13:5, s. 355-361
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Journal article (peer-reviewed)abstract
- Although pain is a frequent problem among elderly patients, they are often omitted in clinical trials and few studies have focused on assessing pain relief in this population. The aim of this study was to compare geriatric patients' verbally reported effect of analgesics with changes in pain experience rated with four different rating scales: the Visual Analogue Scale (VAS), the Graphic Rating Scale (GRS), the Numeric Rating Scale (NRS), and the Pain Relief Scale (PRS). Altogether 53 geriatric patients (mean=82 yrs) with non-pathological fractures in 4 geriatric units at a large university hospital were selected. In connection with the administration of analgesics, the patients were asked to "Mark the point that corresponds to your experience of pain just now at rest" on the VAS, GRS and NRS. This was repeated after 1.5-2 hours, and a direct question was asked about whether the analgesic medication given in connection with the initial assessment had had any pain-alleviation effect. Two comparisons were conducted with each patient. The results show that the probability of accomplishing a rating on the VAS, GRS, NRS, and PRS was lower with advancing age in these elderly fracture patients. The correlations between the ratings of the VAS, GRS and NRS were strong and significant (r=0.80-0.95; p<0.001) both at the initial assessments and at the re-assessments. However, the verbally reported effects of the analgesics were often directly opposite to the changes in rated pain. Therefore, application of the VAS, NRS, GRS and PRS for the purpose of assessing pain relief must be combined with supplementary questions that allow the patient to verbally describe possible experience of pain relief.
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| 7. |
- Bergh, Ingrid, 1956, et al.
(author)
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Descriptions of pain in elderly patients following orthopaedic surgery.
- 2005
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In: Scandinavian journal of caring sciences. - : Wiley. - 0283-9318 .- 1471-6712. ; 19:2, s. 110-8
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Journal article (peer-reviewed)abstract
- The aims of this study were to investigate what words elderly patients, who had undergone hip surgery, used to describe their experience of pain in spoken language and to compare these words with those used in the Short-Form McGill Pain Questionnaire (SF-MPQ) and Pain-O-Meter (POM). The study was carried out at two orthopaedic and two geriatric clinical departments at a large university hospital in Sweden. Altogether, 60 patients (mean age =77) who had undergone orthopaedic surgery took part in the study. A face-to-face interview was conducted with each patient on the second day after the operation. This was divided into two parts, one tape-recorded and semi-structured in character and one structured interview. The results show that a majority of the elderly patients who participated in this study verbally stated pain and spontaneously used a majority of the words found in the SF-MPQ and in the POM. The patients also used a number of additional words not found in the SF-MPQ or the POM. Among those patients who did not use any of the words in the SF-MPQ and the POM, the use of the three additional words 'stel' (stiff), 'hemsk' (awful) and 'rad(d)(sla)' (afraid/fear) were especially marked. The patients also combined the words with a negation to describe what pain was not. To achieve a more balanced and nuanced description of the patient's pain and to make it easier for the patients to talk about their pain, there is a need for access to a set of predefined words that describe pain from a more multidimensional perspective than just intensity. If the elderly patient is allowed, and finds it necessary, to use his/her own words to describe what pain is but also to describe what pain is not, by combining the words with a negation, then the risk of the patient being forced to choose words that do not fully correspond to their pain can be reduced. If so, pain scales such as the SF-MPQ and the POM can create a communicative bridge between the elderly patient and health care professionals in the pain evaluation process.
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| 8. |
- Bergh, Ingrid, 1956, et al.
(author)
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Pain and its relation to cognitive function and depressive symptoms: a Swedish population study of 70-year-old men and women.
- 2003
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In: Journal of pain and symptom management. - : Elsevier. - 0885-3924 .- 1873-6513. ; 26:4, s. 903-12
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Journal article (peer-reviewed)abstract
- The aim of this study was to investigate the prevalence of pain and its characteristics, and to examine the association of pain with cognitive function and depressive symptoms, in a representative sample of 70-year-old men and women. Data were collected within the gerontological and geriatric population studies in G?teborg, Sweden (H-70). A sample of 124 men and 117 women living in the community took part in the study. A questionnaire was applied which included four different aspects of pain experience: prevalence, frequency of episodes of pain, duration and number of locations. In close connection to this, depressive symptoms were assessed using the Center for Epidemiological Studies Depression Scale. The prevalence of pain during the last 14 days was higher in women (79%; n=91) than in men (53%; n=65) (P<0.001). Women (68%; n=78) also reported pain that had lasted for >6 months to a greater extent than men (38%; n=46) (P<0.001). The frequency of episodes of pain was also higher among women, 64% (n=74) reporting daily pain or pain several days during the last 14 days while 37% of the men (n=45) did so (P<0.001). Women (33%, n=38) also reported pain experience from >/=3 locations more often than men (11%; n=13) (P<0.001). On the other hand, the association between depressive symptoms and pain experience was more evident in men than in women. Women were taking significantly more antidepressants compared to men (P<0.03). The results show that pain is common in 70-year-old people and especially in women. However, associations between depressive symptoms and the four aspects of pain experience were more pronounced among men.
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| 9. |
- Bergman, Annika, et al.
(author)
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No germline mutations in supposed tumour suppressor genes SAFB1 and SAFB2 in familial breast cancer with linkage to 19p.
- 2008
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In: BMC Medical Genetics. - : BioMed Central. - 1471-2350. ; 9
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Journal article (peer-reviewed)abstract
- BACKGROUND: The scaffold attachment factor B1 and B2 genes, SAFB1/SAFB2 (both located on chromosome 19p13.3) have recently been suggested as tumour suppressor genes involved in breast cancer development. The assumption was based on functional properties of the two genes and loss of heterozygosity of intragenic markers in breast tumours further strengthened the postulated hypothesis. In addition, linkage studies in Swedish breast cancer families also indicate the presence of a susceptibility gene for breast cancer at the 19p locus. Somatic mutations in SAFB1/SAFB2 have been detected in breast tumours, but to our knowledge no studies on germline mutations have been reported. In this study we investigated the possible involvement of SAFB1/SAFB2 on familiar breast cancer by inherited mutations in either of the two genes.RESULTS: Mutation analysis in families showing linkage to the SAFB1/2 locus was performed by DNA sequencing. The complete coding sequence of the two genes SAFB1 and SAFB2 was analyzed in germline DNA from 31 affected women. No missense or frameshift mutations were detected. One polymorphism was found in SAFB1 and eight polymorphisms were detected in SAFB2. MLPA-anlysis showed that both alleles of the two genes were preserved which excludes gene inactivation by large deletions.CONCLUSION: SAFB1 and SAFB2 are not likely to be causative of the hereditary breast cancer syndrome in west Swedish breast cancer families.
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| 10. |
- Biel, Anders
(author)
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Mechanical behaviour of adhesive layers : experimental methods, cohesive laws, and fracture mechanics
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Adhesive joining is today viewed as one of the key technologies to achieve decreased emissions in the automobile industry. To decrease weight, optimal material selection often results in different materials for different parts. This leads to the necessity to join mixed material. Here, the use of adhesives is the most promising joining technology. For a rational design process, good models for strength analysis of adhesively joined structures are essential. With cohesive modelling, fracture of the adhesive layer is modelled with a stress-deformation law. This law - often denoted a cohesive law - gives the traction exerted on the adherends due to the deformation of the adhesive layer. This thesis is concerned with experimental methods to measure cohesive properties of engineering adhesives and standardized methods to measure the fracture energy of adhesives. A new method to measure cohesive laws is developed. With this method, the cohesive law of an epoxy adhesive is measured in shear. In peel loading, with elastically deforming adherends, the cohesive law is shown to be independent of the geometry of the specimen. If the adherends deform plastically the fracture energy increases. Experiments are performed in order to determine the temperature dependence of the cohesive layer for an epoxy adhesive. It is shown that the peak stress is strongly dependent on the temperature while the fracture energy shows only small temperature dependence. Experiments are also performed to study the influence of strain rate in peel and shear loading. The experiments show that the peak stress increases with an increasing strain rate and that the fracture energy increase in peel loading and decreases in shear with increasing strain rate. A new method to experimentally determine the relation between damage and plasticity in the adhesive during the fracture process is developed. For the present adhesive, it is shown that only minor plasticity occurs during the fracture process in peel loading. For peel, several commonly used methods to evaluate the fracture energy using the double cantilever beam specimen are critically studied. For some methods the error in evaluated fracture energy is larger than 40 %. It is shown that the evaluated fracture energy is more dependent on the choice of method than on the cohesive properties of the adhesive layer.
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