Daniel J. S. Gonçalves

Comparative analysis of drills for composite laminates

The characteristics of carbon fiber-reinforced plastics allow a very broad range of uses. Drilling is often necessary to assemble different components, but this can lead to various forms of damage, such as delamination which is the most severe. However, a reduced thrust force can decrease the risk of delamination. In this work, two variables of the drilling process were compared: tool material and geometry, as well as the effect of feed rate and cutting speed. The parameters that were analyzed include: thrust force, delamination extension and mechanical strength through open-hole tensile test, bearing test, and flexural test on drilled plates. The present work shows that a proper combination of all the factors involved in drilling operations, like tool material, tool geometry and cutting parameters, such as feed rate or cutting speed, can lead to the reduction of delamination damage and, consequently, to the enhancement of the mechanical properties of laminated parts in complex structures, evaluated by open-hole, bearing, or flexural tests.

Physical Inactivity is a Major Contributor to Ovariectomy-Induced Sarcopenia

Since the mechanism(s) underlying menopause-related sarcopenia remain unknown we aimed to investigate the role of physical inactivity in its etiology. Ovariectomized and sham-operated rats were allocated into 2 experimental groups: (1) sedentary-standard housing; and (2) exercise-housed with running wheel. After a 9-month experimental period, soleus muscle structure and biochemical properties were analyzed. No differences existed in muscle fibre size or ultrastructure between sedentary sham and ovariectomized animals housed in standard conditions. In the exercise groups, average daily running distance was 10-fold less in ovariectomized compared to sham-animals. Further, in exercised animals, soleus fibre size was smaller in ovariectomized compared to sham-animals. Nonetheless, compared to both sedentary groups, muscle fibre size was larger in the exercised ovariectomized animals. Our results indicate that ovariectomy-induced sarcopenia is not due to the loss of ovarian hormones per se, but is largely due to physical inactivity.

Lifelong Sedentary Behaviour and Femur Structure

The aim of the present study was to analyze the lifelong differences of femur structure in sedentary and physically active animal models. Thirty male C57BL/6 mice, 2 months old, were either: i) housed in cages with running wheel (AA; n=10), ii) housed in cages without running wheel (AS; n=10), iii) or sacrificed without intervention (Y; n=10). AA and AS animals were sacrificed after 23 months of housing. Right femur structure was analyzed in all animals by histomorphometry. Significant differences in several microarchitectural parameters of cancellous and cortical bone were identified between Y mice and both groups of aged mice, as well as between AA and AS groups. Lifelong physically active mice had significantly higher cancellous bone surface (Cn.BS) and trabecular number (Tb.N) and decreased trabecular separation (Tb.Sp) at both epiphyses when compared to AS animals. No differences were observed between Y and AA groups regarding osteocyte number (N.Ot) despite its significant reduction in AS animals, suggesting that age alone was not a cause for decreases in N.Ot. Our results suggest that the reduced bone quality observed in the elderly is not only a consequence of age but also of lack of physical activity since sedentary behaviour significantly aggravated the degenerative age-related bone differences.

Drilling of Carbon Fibre Reinforced Laminates - A Comparative Analysis of Five Different Drills on Thrust Force, Roughness and Delamination

The distinguishing characteristics of carbon fibre reinforced laminates, like low weight, high strength or stiffness, had resulted in the increase of their use during the last decades. Although parts are normally produced to “near-net” shape, machining operations like drilling are still needed. In result of composites non-homogeneity, this operation can lead to delamination, considered the most serious kind of damage as it can reduce the load carrying capacity of the joint. A proper choice of tool and cutting parameters can reduce delamination substantially. In this work, the results obtained with five different tool geometries are compared. Conclusions show that the choice of adequate drill geometry can reduce the thrust forces and consequently, the delamination damage.

Delamination in carbon/epoxy plates drilling: tool and feed rate effect

The attractive characteristics of carbon fibre reinforced plastics had their widespread use. In order to join different components, drilling is often necessary. It is known that a drilling process that reduces the drill thrust force can decrease the risk of delamination. In this work, three combinations of the drilling process are compared: tool diameter, tool geometry and feed rate. The parameters studied were: thrust force, delamination extension and mechanical strength of the drilled region-bearing test. This work demonstrates that a proper combination of the drilling variables can contribute to reduce the delamination damage and, consequently, enhance mechanical resistance of the joint.

Evaluation of Tools and Cutting Conditions on Carbon Fibre Reinforced Laminates

The distinctive characteristics of carbon fibre reinforced plastics, like low weight or high specific strength, had broadened their use to new fields. Due to the need of assembly to structures, machining operations like drilling are frequent. In result of composites inhomogeneity, this operation can lead to different damages that reduce mechanical strength of the parts in the connection area. From these damages, delamination is the most severe. A proper choice of tool and cutting parameters can reduce delamination substantially. In this work the results obtained with five different tool geometries are compared. Conclusions show that the choice of an adequate drill can reduce thrust forces, thus delamination damage.