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This paper is concerned with evaluation and prediction of the tensile properties of carbon fiber-reinforced plastics laminates considering the strain rate effect at intermediate strain rates. Uniaxial tensile tests of carbon fiber-reinforced plastics laminates were conducted at various strain rates ranging from 0.001 s–1 to 100 s–1 using Instron 8801 and a high speed material testing machine to measure the variation of the elastic modulus and the ultimate tensile strength. Tensile test specimens were designed based on the ASTM standards and stacked unidirectionally such as [0°], [90°] and [45°] to predict the elastic modulus of carbon fiber-reinforced plastics laminates with various stacking sequences. The axial strain was measured by the digital image correlation method using a high speed camera and ARAMIS software to enhance the accuracy of the strain measurement. A prediction model of the elastic modulus of carbon fiber-reinforced plastics laminates is newly proposed in consideration of the laminate theory and the tensile properties of unidirectional carbon fiber-reinforced plastics laminates. The prediction model was utilized to predict the tensile properties of [0°/90°]s laminates, [±45°]s laminates, and [0°/±45/90°]T laminates for validation of the model. The elastic moduli predicted were compared with the static and dynamic tensile test results to confirm the accuracy of the prediction model.

Tensile behaviors of aluminum/carbon fiber reinforced polymer hybrid composites with different carbon fiber reinforced polymer stacking sequences were measured at strain rates between 0.001/s and 100/s and properties of the hybrid composites were compared to the results of aluminum and carbon fiber reinforced polymer tested under the same conditions. In the aluminum specimen, negative strain rate sensitivity resulted in a significant decrease in the tensile strength and positive strain rate sensitivity resulted in an increase in failure strain at higher strain rates. However, in the hybrid composite specimen, both the tensile strength and the failure strain could be increased as the strain rate increased by reinforcing the aluminum with carbon fiber reinforced polymer. The differences in tensile properties and the degree of strain rate sensitivity were extensive depending on the stacking sequence of the carbon fiber reinforced polymer layer. A Weibull function with scale parameter σ0 and shape parameter β was used in order to describe the relation between stress and strain of aluminum/carbon fiber reinforced polymer hybrid composites, and the constitutive equation established by the Weibull function described the tensile behavior of the hybrid composites very well.

ObjectiveTo report the characteristics of myofascial trigger points (MTrPs) in the infraspinatus muscle and evaluate the therapeutic effect of trigger-point injections.MethodsMedical records of 297 patients (221 women; age, 53.9±11.3 years) with MTrPs in the infraspinatus muscle were reviewed retrospectively. Because there were 83 patients with MTrPs in both infraspinatus muscles, the characteristics of total 380 infraspinatus muscles with MTrPs (214 one side, 83 both sides) were investigated. Specific characteristics collected included chief complaint area, referred pain pattern, the number of local twitch responses, and distribution of MTrPs in the muscle. For statistical analysis, the paired t-test was used to compare a visual analogue scale (VAS) before and 2 weeks after the first injection.ResultsThe most common chief complaint area of MTrPs in the infraspinatus muscle was the scapular area. The most common pattern of referred pain was the anterolateral aspect of the arm (above the elbow). Active MTrPs were multiple rather than single in the infraspinatus muscle. MTrPs were frequently in the center of the muscle. Trigger-point injection of the infraspinatus muscle significantly decreased the pain intensity. Mean VAS score decreased significantly after the first injection compared to the baseline (7.11 vs. 3.74; p<0.001).ConclusionCharacteristics of MTrPs and the therapeutic effects of trigger-point injections of the infraspinatus muscle were assessed. These findings could provide clinicians with useful information in diagnosing and treating myofascial pain syndrome of the infraspinatus muscle.